Section II - Equipment Piping and Assembly Applications

8/8/2019 Section II - Equipment Piping and Assembly Applications

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Section II - Equipment Piping and Assembly Applications

Back To Main

A: General Guidelines for Equipment and Piping Location, Spacing, Distances and Clearances-

By: James O. Pennock

This article is intended to aid both the novice and experienced piping designer with guidance for plot

plan development.

C1: Introduction to Vessels and Vessel Orientation - By: James O. Pennock

C2: Vertical Vessel Orientation - By: James O. Pennock

(BACK TO TOP)

Section - II

A: General Guidelines for Equipment and Piping Location, Spacing, Distances

and Clearances


This article should only be used as a guide. It's intended purpose is to help the piping designer who is

responsible for placement of one specific item in a typical refinery, chemical or petrochemical process

plant or someone who may need help in developing a total plot plan for a complex unit.

The guidelines given here are based on my many years of experience with one of the world's largest

engineering, design and construction companies along with the U. S. OSHA Part 1910 and the NFPA

(National Fire Protection Association) Code No. 30. The latest editions of these codes and any other

applicable national, regional and local codes should be referred to and used because they may be more

stringent. The subjects covered in this article have been arranged in alphabetical order in the hope it

will make them easier to locate.

Access (See Maintenance)

Columns (See Vertical Vessels)

Compressors, Centrifugal

Locate centrifugal compressor as close as possible the suction source. Top suction and discharge lines

either should be routed to provide clearance for overhead maintenance requirements, or should be

made up with removable spool pieces.


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Support piping so as to minimize dead load on compressor nozzles; the load should be within the

recommended allowance of the compressor manufacturer.

Centrifugal compressors should have full platforming at operating level. Heavy parts such as upper or

inner casing and rotor should be accessible to mobile equipment. Review the equipment arrangement

for access and operation.

Locate lube and seal oil consoles adjacent to and as close as possible to the compressor. Oil return lines

from the compressor and driver should have a minimum slope of 1/2 inch per foot to the inlet

connection of seal traps, degassing tanks, and oil reservoir. Pipe the reservoir, compressor bearing, and

seal oil vents to a safe location at least 6 feet above operator head level.

Compressors, Reciprocating

Locate reciprocating compressors so suction and discharge lines that are subject to vibration

(mechanical and acoustical) may be routed at grade and held down at points established by a stress and

analog study of the system.

Accessibility and maintenance for large lifts such as cylinder, motor rotor, and piston removal should be

by mobile equipment if the installation is outdoors or by traveling overhead crane if the installation is

indoors (or covered).

Horizontal, straight line, reciprocating compressors should have access to cylinder valves. Access should

be from grade or platform if required.

Depending on unit size and installation height, horizontal-opposed and gas engine driven reciprocating

compressors may require full platforming at the operating level.

Control Valves

Locate control valve stations accessible from grade or on a platform. In general, the (flow, level,

pressure, temperature) instruments or indicators showing the process variables should be visible from

the control valve.

Cooling Towers

Locate cooling towers downwind of buildings and equipment to keep spray from falling on them. Orient

the short side of the tower into the prevailing summer wind for maximum efficiency. This means that

the air flow (wind) will travel up the long sides and be drawn in to both sides of the cooling towerequally. When the wind is allowed to blow directly into one long side it tends to blow straight through

and results in lower efficiency. Locate cooling towers a minimum of 100 feet (30m) from process units,

utility units, fired equipment, and process equipment.

Cradles (See Insulation Shoes and Cradles)

Equipment Arrangement (General)


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Arrange equipment, structures, and piping to permit maintenance and service by means of mobile

equipment. Provide permanent facilities where maintenance by mobile equipment is impractical. Group

offsite equipment, pumps, and exchangers to permit economical pipe routing. Locate this equipment

outside of diked storage areas.

Exchanger, Air Cooler (Fin Fans)

Air Coolers are in typically used in the cooling of the overhead vapor from tall vertical vessels or towers

such as Crude Fractionators and Stripper Columns. The natural flow tends to follow gravity, where the

tower overhead is the high point then down to the Air Cooler, then down to the Accumulator and finally

the Overhead Product transfer pumps. With this in mind the Air Coolers are normally located above

pipeways. This conserves plot space and allows the pipe rack structure with it's foundation to do double

duty with only minor up grade to the design. If the pipe rack is not used then plot space equal to the size

of the Air Cooler is required. In addition a totally separate foundation and stand alone structure is

required.

Exchanger, "G" Fin (Double Pipe)

These exchangers can be mounted almost anywhere any they can be mounted (with process engineer

approval) in the vertical when required. A G-Fin Exchanger is recognizable by its shape. One segment

looks like two long pieces of pipe with a 180 degree return bend at the far end. It is one finned pipe

inside of another pipe with two movable supports. This type of exchanger can be joined together very

simply to form multiples in series, in parallel or in a combination of series/parallel to meet the

requirements of the process. This exchanger is not normally used in a service where there is a large flow

rate or where high heat transfer is required. The key feature with this exchanger is the maintenance.

The piping is disconnected from the tube side (inner pipe). On the return bend end of this exchanger

there is a removable cover. When the cover is removed this allows for the tube (inside pipe) to be pulledout. This exchanger is normally installed with the piping connections toward the pipe rack.

Exchangers, Reboiler (Kettle Reboiler)

Locate kettle reboilers at grade and as close as possible to the vessel they serve. This type of reboiler is

identifiable by its unique shape. It has one end much like a normal Shell and Tube exchanger then a very

large eccentric, bottom flat transition to what looks like a normal horizontal vessel. You could also call it

a "Fat" exchanger. The flow characteristics on the process side of a kettle reboiler are the reason for the

requirement for the close relationship to the related vessel.

Reboilers normally have a removable tube bundle and should have maintenance clearance equal to thebundle length plus 5 feet (1.5m) measured from the tube sheet.

Exchangers, Shell and Tube

Shell and tube exchangers should be grouped together wherever possible. Stacked shell and tube

exchangers should be limited to four shells high in similar service; however, the top exchanger should

not exceed a centerline elevation of 18 feet (5.5m) above high point of finished surface, unless mounted


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in a structure. Keep channel end and shell covers clear of obstructions such as piping and structural

members to allow unbolting of exchanger flanges, and removal of heads and tube bundles.

Exchangers with removable tube bundles should have maintenance clearance equal to the bundle

length plus 5 feet (1.5m) measured from the tube sheet to allow for the tube bundle and the tube

puller.

Maintenance space between flanges of exchangers or other equipment arranged in pairs should be 1'-

6" (0.5m) (min.). Exchanger maintenance space from a structural member or pipe should not be less

than 1'- 0" (300mm) (min.).

Furnaces (Fired Equipment)

Locate fired equipment, if practical, so that flammable gases from hydrocarbon and other processing

areas cannot be blown into the open flames by prevailing winds. Horizontal clearance from hydrocarbon

equipment (shell to shell) 50'- 0" (15m) Exception: Reactors or equipment in alloy systems should be

located for economical piping arrangement. Provide sufficient access and clearance at fired equipmentfor removal of tubes, soot blowers, air preheater baskets, burners, fans, and other related serviceable

equipment. Clearance from edge of roads to shell 10'- 0"(3m) Pressure relief doors and tube access

doors should be free from obstructions. Orient pressure relief doors so as not to blow into adjacent

equipment. The elevation of the bottom of the heater above the high point of the finished surface

should allow free passage for operation and maintenance.

Furnace Piping

Locate snuffing steam manifolds and fuel gas shutoff valves a minimum of 50 feet (15m) horizontally

from the heaters they protect. Burner Valving for a Floor Fired Furnaces: Combination oil and gas firing

valves should be operable from burner observation door platform. For those fired by gas only, the valves

should be near the burner and should be operable from grade.

Burner Valving for a Side Fired Furnaces: Locate firing valves so they can be operated while the flame is

viewed from the observation door.

Flare Stacks

Locate the flare stack upwind of process units, with a minimum distance of 200 feet (60m) from process

equipment, tanks, and cooling towers. If the stack height is less than 75 feet (25m), increase this

distance to a minimum of 300 feet (90m). These minimum distances should be verified by Company

Process Engineering.

Future Provisions

Space for future equipment, pipe, or units should not be provided unless required by the client or for

specific process considerations. When applicable this requirement should be indicated on the plot plan

and P&IDs.


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Insulation Shoes and Cradles

Locate Insulation shoes anywhere a line crosses a support for hot insulated piping when the piping is 3

inch (80mm) and larger carbon and alloy steel lines with design temperatures over 650 degrees F (350C).

Large diameter lines (20 inches (500mm) and over), stainless steel lines where galvanic corrosion may

exist, lines with wall thickness less than standard weight, and vacuum lines should be analyzed todetermine if shoes or wear plates are needed.Provide cradles at supports for insulated lines in cold

service and for acoustical applications.

Ladders & Cages

Maximum height of a ladder without a cage should not exceed 15'-0" (4.5m)

Maximum vertical distance between platforms 30'- 0" (9m)

Cages on ladders over 15'-0" (4.5m) high shall start at 8'-0" (2.5m) above grade.

Minimum toe clearance behind a ladder 0'- 7" (200mm)

Minimum handrail clearance 0'- 3" (80mm)

Level Instruments

Locate liquid level controllers and level glasses so as to be accessible from grade, platform, or

permanent ladder. The level glass should be readable from grade wherever practical. Wherever

possible, orient level instruments on the side toward the operating aisle.

Loading Racks

Locate loading and unloading facilities that handle flammable commodities a minimum of 200 feet

(60m) from away from process equipment, and 250 feet (75m) from tankage.

Maintenance Aisles (at grade)

Equipment maintenance aisle for hydraulic crane (12T capacity) should have a horizontal clearance

width of 10'- 0" (3m) (min.) and a vertical clearance of 12'- 0" (3.5m) (min.). Where a fork lift and similar

equipment (5000 lbs / 230kg capability) is to be used the horizontal clearance should be 6'- 0" (2m)

(min.) and the vertical clearance should be 8'- 0" (2.5m) (min.).

Where maintenance by portable manual equipment (A-frames, hand trucks, dollies, portable ladders or

similar equipment) is required the horizontal clearance should be 3'- 0" (1m) (min.) and the vertical

clearance 8'- 0" (2.5m) (min.).

Operating Aisle (at grade)

Minimum width 2'- 6" (800mm)

Headroom 7'- 0" (2.1m)


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Orifice Runs and Flanges

Locate Orifice runs in the horizontal. Vertical orifice runs may only be used with the approval of

Company Control Systems Engineering. Orifice flanges with a centerline elevation over 15 feet (4.5m)

above the high point of finished surface, except in pipeways, should be accessible from a platform or

permanent ladder.

Locate orifice taps as follows:

Air and Gas

-Top vertical centerline (preferred)

-45 degrees above horizontal centerline (alternate)]

Liquid and Steam

-Horizontal centerline (preferred)

-45 degrees below horizontal centerline (alternate]

(Note: The piping isometrics should show the required tap orientations)

Personnel Protection

Locate eye wash and emergency showers in all areas where operating personnel are subject to

hazardous sprays or spills, such as acid.

Personnel protection should be provided at uninsulated lines and for equipment operating above 140

degrees F (60 C) when they constitute a hazard to the operators during the normal operating routine.

Lines that are infrequently used, such as snuffing steam and relief valve discharges, may not require

protective shields or coverings.

Pipe

Clearance between the outside diameter of flange and the outside diameter of pipe to the insulation

should not be less than 0'- 1"* (25mm)

Clearance between the outside diameter of pipe, flange, or insulation and structural any member should

not be less than 0'- 2"* (50mm)

*With full consideration of thermal movements

Platforms

Minimum width for ladder to ladder travel: 2'- 6" (800mm)

Headroom: 7'- 0" (2.1m)


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Headroom from stairwell treads: 7'- 0" (2.1m)

Minimum clearance around any obstruction on dead end platforms: 1'- 6" (500mm)

Pressure Instruments

Locate all local pressure indicators so they are visible from grade, permanent ladder, or platform. Those

located less than 15 feet (4.5m) above high point of finished surface should be accessible from grade or

a portable ladder. Those located in a pipeway should be considered accessible by portable ladder. Those

over 15 feet (4.5m) above high point of finished surface should be accessible from a platform or

permanent ladder.

Process Units

The relation of units, location of equipment, and routing of pipe should be based on economics, safety,

and ease of maintenance, operation, and construction requirements. The alignment of equipment and

routing of pipe should offer an organized appearance.

Process Unit Piping

Locate all pipe lines in major process units on overhead pipeways. In certain instances, pipes may be

buried, providing they are adequately protected. Lines that must be run below grade, and must be

periodically inspected or replaced, should be identified on the P&IDs and placed in covered concrete

trenches.

Cooling water lines normally may be run above or below ground, based on economics.

Domestic or potable water and fire water lines should be run underground.

Pumps

Locate pumps close to the equipment from which they take suction. Normally, locate pumps in process

units under pipeways.

Design piping to provide clearance for pump or driver removal. Similarly, on end suction pumps, piping

should permit removing suction cover and pump impeller while the suction and discharge valves are in

place.

Arrange suction lines to minimize offsets. The suction lines should be short and as direct as possible, andshould step down from the equipment to the pump. Suction lines routed on sleeperways may rise to

pump suction nozzle elevation.

Orient valve handwheels or handles so they will not interfere with pump maintenance or motor

removal. Valve handwheels or handles should be readily operable from grade.


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Maintenance and operating aisles with a minimum width of 2'-6" (800mm) should be provided on three

sides of all pumps.

Pump Strainers

Provide temporary conical type strainers in 2 inch (50mm) and larger butt weld pump suction lines for

use during startup. Arrange piping to facilitate removal.

Use permanent Y-type strainers on 2 inch (50mm) and smaller screwed or socket weld pump suction

piping.

Railroads

Headroom over through-railroads (from top rail) 22'- 6"** (7m)

Clearance from track centerline to obstruction 10'- 0"** (3m)

(** Verify conformance with local regulations)

Relief Valves (Pressure, Safety and Thermal)

Locate all relief valves so they are accessible. Wherever feasible, locate them at platforms that are

designed for other purposes. Relief valves with a centerline elevation over 15 feet (4.5m) above high

point of finish surface (except in pipeways) should be accessible from platform or permanent ladder.

Pressure relief valves that discharge to a closed system should be installed higher than the collection

header. There should be no pockets in the discharge line.

Safety relief valves (in services such as steam, etc.) that discharge to the atmosphere should have tail

pipes extended to a minimum of 8 feet (2.5m)above the nearest operating platform that is within a

radius of 25 feet (7.5m). This requirement may be waived, provided a review of the proposed

arrangement indicates that it does not present a hazard. Review all pressure and safety relief valves

discharging flammable vapors to the atmosphere within 100 feet (30m) of fired equipment for vapor

dissipation.

Pressure and Safety relief valves, 1-1/2 inch (40mm) and larger, should only be installed with the stem

and body vertical position.

Thermal relief valves, 1 inch (25mm) and smaller, may be installed with the stem and body in a

horizontal position when it is impractical to install it in the vertical position.

Roads

Major process plants normally have three classes of roads. They might be called Primary roads,

Secondary roads and Maintenance access ways.

Clearance or Vertical Width Shoulder Side or off road


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distance

requiredRoad type

Primary 21'-0" (6.5m) 20'-0" (6m) 5'-0" (1.5m) 20'-0" (6m)

Secondary (*) 12'-0" (3.7m) 12'-0" 3.7m) 3'-0" (1m) 10'-0" (3m)

Maintenance

access

10'-0" (3m) 10'-0" (3m) (not req'd) 5'-0" (1.5m)

(*) Normally secondary plant roads may be used as tube pull areas.

Safety Access

Provide a primary means of egress (continuous and unobstructed way of exit travel) from any point in

any building, elevated equipment, or structure. A secondary means of escape should be provided where

the travel distance from the furthest point on a platform to an exit exceeds 75 feet (25m).

Access to elevated platforms should be by permanent ladder. Safety cages should be provided on all

ladders over 15'-0" (4.5m)

The need for stairways should be determined by platform elevation, number of items requiring

attention, observation and adjustment, and the frequency of items.

Ladder safety devices such as cable reel safety belts and harnesses, may be investigated for use on

boiler, flare stack, water tank, and chimney ladders over 20 feet (6m) in unbroken lengths in l ieu of cage

protection and landing platforms.

Sample Connections

Locate all sample connections so they are readily accessible from grade or platform.

In general, where liquid samples are taken in a bottle, locate the sample outlet above a drain funnel to

permit free running of the liquid before sampling.

Hot samples should be provided with a cooler.

Sleeper Pipe Supports

Normally, route piping in offsite areas on sleepers. Stagger the sleeper elevations to permit ease of

crossing or change of direction at intersections. Flat turns may be used when entire sleeper ways change

direction.

Spectacle Blinds

Locate spectacle blinds to be accessible from grade or platform. Blinds located in a pipeway are

considered accessible. Blinds that weigh over 100 lbs (45kg) should be accessible by mobile equipment.

Where this is not possible, provide davits or hitching points.

Closely grouped flanges with blinds should be staggered.


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Steam Traps

Locate all steam traps at all pocketed low points and at dead ends of steam headers. Also, provide traps

periodically on excessively long runs of steam piping, for sufficient condensate removal, and to ensure

dry quality steam at destination. Steam traps should be accessible from grade or a platform. Steam traps

located in pipeways should be considered accessible by portable ladder.

Tankage

Locate any tankage containing hydrocarbon or other combustible fluids or gasses a minimum distance of

250'-0" (115m) from any process unit, rail loading facility or truck loading facility.

The minimum spacing of offsite storage tanks and dike requirements should be in accordance with the

latest edition of the National Fire Protection Association, Code No. 30, and OSHA part 1910.106 (b),

where applicable.

Temperature Instruments

Locate temperature test wells, temperature Indicators and thermocouples to be accessible from grade

or a portable ladder. Those located in a pipeway should be considered accessible by a portable ladder.

Those located over 15 feet (7m) above high point of finished surface should be accessible from a

platform or permanent ladder.

Locate all local temperature indicators (TI) should be visible from grade, ladder, or platform.

Towers (See Vertical Vessel)

Utility Stations

Provide and locate utility stations with water, steam, or air as indicated below:

All areas should be reachable with a single 50 foot (20m) length of hose from the station.

Provide water outlets at grade level only, in pump areas, and near equipment that should be water

washed during maintenance.

Provide steam outlets at grade level only in areas subject to product spills, and near equipment that

requires steaming out during maintenance.

Provide air outlets in areas where air-driven tools are used such as at exchangers, both ends of heaters,

compressor area, top platform of reactors, and on columns at each manway.

Hose, hose rack, and hose connections should be provided by the client or be purchased to match the

clients existing hardware.

Valve Handwheel Clearance


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Clearance between the outside of hand wheel and any obstruction (knuckle clearance) should be 0'- 3"

(80mm)

Valve Operation

Locate operating valves requiring attention, observation, or adjustment during normal plant operation

(noted on the P&IDs) so they may be within easy reach from grade, platform, or permanent ladder as

follows:

- 2" (50mm) and smaller may be located reachable from a ladder.

- 3" (80mm) and larger must be reachable and operable on a platform

Operating valves with the bottom of handwheel is over 7 feet (2.1m)above high point of finished surface

or operating platform may be chain-operated.

The centerline of handwheel or handles on block valves used for shutdown only, located less than 15

feet (4.5m) above high point of finished surface, and those located in pipeways, may be accessible by

portable ladder.

The centerline of handwheel or handles on block valves used for shutdown only and located over 15 feet

(4.5m) above high point of finished surface, except those located in pipeways, should be operable from

permanent ladder or platform.

In general, keep valve handwheels, handles, and stems out of operating aisles. Where this is not

practical, elevate the valve to 6'- 6" (plus or minus 3 inches) clear from high point of finished surface to

bottom of handwheel.

Vents and Drains

The P&IDs should indicate, locate and size all vents, drains, and bleeds required for process reasons and

plant operation.

Provide plugged hydrostatic vents and drains without valves at the high and low points of piping.

Provide valved bleeds at control valve stations, level switches, level controllers, and gage glasses per job

standard.

Vertical Vessel (Column) Piping and Platforms

Locate vertical vessels in the equipment rows on each side of the pipeway in a logical order based on the

process and cost. The largest vessel in each equipment row should be used to set the centerline location

of all vertical vessels in that equipment row. This largest vertical vessel should be set back from the pipe

rack a distance that allows for; any pumps, the pump piping, an operation aisle between the pump

piping and any piping in front of the vessel, the edge of the vessel foundation and half the diameter of

this the largest vessel. Set all other vertical vessels in this same equipment row on the same centerline.


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Provide a clear access area at grade for vessels with removable internals or for vessels requiring loading

and unloading of catalyst or packing. Provide vessel davits for handling items such as internals and relief

valves on vessels exceeding a height of 30 feet (9m) above the high point of the finished surface, and on

vessels not accessible by mobile crane. Orient davits to allow the lowering of appurtenances into the

access area.

Walkways

Walkways should have a 2'-6' (1m) horizontal clearance (not necessarily in a straight

line) and headroom of 7'- 0" (2.1m)

(BACK TO TOP)

Section - II

C: Introduction to Vessels and Vessel Orientation


The question on many minds may be "Why does Piping do Vessel Orientation?" We can answer that

question two ways. The first answer would be, because of the traditional role of Piper and the content

of the vessel orientation activity itself. The traditional role of the Piper has always been the bringing

together of multi-discipline information to create the plant layout and piping plans. The activity of vessel

orientation has the same multi-discipline focus.

The second way to answer the question is to ask "If not the Piper, then who?" Civil? Structural?

Electrical? Instrumentation? No, they are not logical candidates. Structural? The structural engineer

does engineer the support for some vessels but they do not truly design the support. Process? While the

process engineer does have a great deal of interest and input in the workings of a vessel, their interest is

more from a function and performance focus. Vessels? Why doesn't the vessel engineer do the vessel

orientation? Or better yet, why doesn't the Vendor do the vessel orientation? The response to that is in

all of the non-vessel factors that influence the vessel orientation activity. What are non-vessel factors?

Non-vessel factors include:

A. Site -- Vessel orientation is influenced by where the vessel is located on the site

B. Relationship to related equipment -- Proper vessel orientation must consider the location and method

of connection to related equipment

C. Support -- Vessel orientation of many vessels includes the method of support


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D. P&ID interpretation -- The person responsible for vessel orientation must be very proficient in reading

and understanding a P&ID

E. Internals to external object relationships -- Internals effect the nozzle locations that in turn connect to

the piping. The piping is subject to thermal expansion, and must be supported. The piping must meet all

the process requirements from the P&ID, and must be in compliance with the Plant Layout DesignSpecification. The piping must also be supported, and must meet the all the applicable Code criteria, etc.

F. Operations and Maintenance -- Vessel orientation must be compatible with the requirements of the

operators and the people who must maintain the vessels.

This brings us back to answer number one. Vessel orientation requires the bringing together of and the

coordination of data and requirements from many disciplines. Piping in their Plant Layout role is already

functioning in this mode. Most major engineering and design firms (in our Industry) have found that

Piping Design is the most logical and most efficient group for developing complex vessel orientations.

The ideal scenario for the development of a vessel orientation is like a chain. The links of the chain arelike the steps required completing the finished design. With the ideal scenario you would not start step

two until step one is completed and so on. The ideal circumstances means that the Plot Plan has been

firmed up and approved, the P&IDs have been developed, reviewed, and issued approved for design

(AFD). It means that the unit piping transposition has been developed. It means that Process has

completed their input to the vessel datasheet and Vessels has completed their preliminary work.

Occasionally, the piping designer has been required to initiate a vessel orientation under other than the

most ideal of circumstances. In some cases the vessel orientation has been started before the P&IDs

were ready for the first Client P&ID review. Starting Vessel orientation before the source documents are

ready will expose the job to risks, errors, recycle and increased costs.

As much as we try to avoid this situation, it can still happen. Premature starts in vessel orientation are

due to the requirement for early purchase of vessels identified as long delivery. The Construction

schedule of any project is based on the delivery of key equipment and materials. The construction

schedule in turn will impact the start-up schedule. Once the Client has awarded the project, they are

anxious to get their plant "on-stream" as soon as possible. The sooner they get on-stream, the sooner

they can recover the capitol investment and see the expected profits.

The delivery time for vessels such as: alloy reactors, heavy wall high pressure vessels, or crude vacuum

columns often take more than a year from PO (purchase order) release to shipment. In the past, one

way to expedite the overall schedule, the Client has pre-purchased the vessels prior to the award of theproject. There is a potential risk for increased cost in this scenario also.

Under normal circumstances a Vessel fabricator will not normally do any rolling and cutting of plate until

the order has reached a certain milestone. They will need the final checked, corrected and approved

vessel drawings. This includes all the nozzles, pipe supports, pipe guides, ladders, platforms, etc. The


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Vendor's fabrication and delivery performance clock does not start ticking until they get the drawings

back approved.

A project with a fast track schedule or pre-purchased vessels will put a lot of pressure on the piping

design group. Piping should normally have time to properly develop the Plot Plan, the P&ID

transposition, the other related piping layouts, in order to come up with the best vessel orientations foreconomics, operability, and maintenance.

As piping designers you owe it to the Client, your company, as well as to yourself to do the best job you

know how. This philosophy is true when doing vessel orientations as with any other piping design

activity. You should check into all aspects of the vessel piping and the orientation. You need to start by

collecting, verifying, and using the proper information.

During Plot Plan development, the piping designer must take into consideration many items that can

also have a bearing on the vessel other than the orientation itself.

Such items include:

Lay-down space -- Prior to erection, tall columns require space for final assembly

Erection equipment -- The cranes (or other lifting devices) planned to lift and set the vessels require vast

amounts of space

Plant road limitations; Rack heights, shoulder clearances, logistics

Special vessels such as Reactors have several factors, which should be kept in mind. The most important

one, of course, is to keep the alloy piping as short as possible by locating the Reactors near the Heaters.

Catalyst handling facilities is another important consideration. This is true whether the catalyst is to be

loaded by crane or by vessel mounted monorail. The removal of spent catalyst, usually by tote bin, truck,

or conveyor, is another space consideration.

We all need to remember space is money to the Client. Wise use of plot space can save the Client

money by reducing installation costs and operating costs.

Vessel Configurations

Vessels come in a wide variety of configurations. The variety is expressed in their sizes, shape, and

function. They also will have a wide range of pressure, temperature and metallurgy. This list is only

intended to highlight the main examples.

Vertical Vessels with no internals

(A.k.a.: Tanks, Drums, and Pots)

Example: Mix Tank, Air Receiver, Volume Bottle, Flash Drums, Fuel Gas K. O. Pot, Feed Surge Drum, and

Dump Tank


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Discussion: This type of vessel will normally be small (< 24" diameter x 3' - 0" T-T) to medium sized

(24"dia to 48" diameter x < 10" - 0" T-T). They may be mounted to the support surface (grade, floor, or

platform) via a traditional vessel skirt, attached legs, or lugs. When located at grade this vessel may be

mounted directly on the concrete paving or floor depending on vessel weight and soil conditions.

Vertical Vessels with simple Internals

Simple internals such as Demister Pads

Example: Feed Knockout Drum, Separator Drum, Filter, and Coalescer Drum

Discussion: This type of vessel will normally be medium (24"dia to 48" diameter x < 10" - 0" T-T) to large

sized (Over 48" diameter and over 10' - 0" T-T). They may be mounted to the support surface (grade or

platforms) via a traditional straight vessel skirt, a flared skirt, attached legs, or lugs. When located at

grade this vessel will normally be mounted on an octagon foundation.

Vertical Trayed Vessels with straight sides

Example: Fractionator, Contactor, and Stripper

Discussion: This type of vessel can be as small as two or three feet in diameter or may be very large at

20' - 0" or more in diameter. The diameter, height, number of trays, type of trays along with the other

related items depends on the function. These vessels will normally be supported at grade via a

traditional vessel skirt. This vessel will normally be supported on the traditional 9" to 1' - 0" high octagon

concrete foundation.

Vertical Trayed Vessels - Coke Bottle (two diameters w/ transition)

Example: Splitter, Stabilizer, Lean Oil Still, and Absorber Column

Discussion: This type of vessel will have two diameters. The Coke Bottle Vessel is a multi purpose vessel.

The larger section will have different internals and function differently than the smaller section. The

bottom of the Column will normally be the larger diameter with a conical transition piece to join the

two. This type vessel will normally be mounted at grade via a traditional vessel skirt and be supported

on an octagon foundation.

Variation: A variation of this type vessel is the Inverted Coke Bottle. The Inverted Coke Bottle Vessel will

normally have a short skirt at the transition point and be mounted on an elevated platform in a

structure. The smaller (lower) section will hang down inside the structure.

Vertical Packed Tower Vessels

Example: Dryers, Feed Purifiers,

Discussion: these types of vessel will normally be medium sized. Packing may be a manufactured mesh

or a granulated natural material. The location and orientation of this type of vessel must consider the

loading and removal of the packing. These vessels may operate at ambient, temperatures, the lower


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Horizontal Vessels - Elevated without Boots

Example: Steam Drum, and Feed Surge Drum

Discussion: these types of vessel will normally be medium to large sized. They will be mounted to the

support surface (foundation or platforms) on traditional vessel saddles. When located near grade this

vessel will normally be mounted on an elevated foundation. The NPSH requirements of the related

pumps are critical to setting of the support elevation.

Horizontal Vessels - Elevated with Boots

Example: Stripper Receiver, Accumulator, Interstage K. O. Drum, and Flare K. O. Drum

Discussion: these types of vessel will normally be medium to large sized. They will be mounted to the

support surface (foundation or platforms) on traditional vessel saddles. When located near grade this

vessel will normally be mounted on an elevated foundation. Access is normally required for the Boot

operating valves and instruments. The NPSH requirements of the related pumps are critical to setting of

the support elevation.

Horizontal - Underground or Pit Vessels

Example: Dump Tank, Kill Tank, and Hazardous Material Storage Tank

Discussion: This type of vessel may be small, medium, or large in size. They will be mounted to the

support surface on traditional vessel saddles. When located at grade this vessel will normally be

mounted on a low foundation. When located in a pit, the pit size must allow for safety, operation, and

maintenance. Pit mounted installations may also require sumps and drainage pumps. Underground

(buried) installations may require double wall tanks with leak detection provisions.

API Storage Tanks

Example: Feed Storage, Intermediate Product Storage, Off-Spec Product Storage, Finished Product

Storage, Batch Storage, Fire (or other) Water Storage

Discussion: These are the traditional Tank Farm tanks. There are a number of sub-types, which include

Cone Roof Atmospheric; Cone Roof with captured venting, Open Floating Roof, Enclosed Floating Roof,

and Double Wall LNG Storage Tanks. These tanks have specific location, support, piping connection,

safety, and access criteria based on the commodity to be stored.

Special

Example: Spheres, Spheroids, and Bullets

Discussion: These vessel types have special location and orientation criteria and should be handled on

an Ad Hoc basis.

Vessel Supports


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There is a wide variety in the methods used to support vessels.

There include:

a. Skirts

b. Saddles

c. Ring Girders

d. Lugs

e. Legs

f. Portables on Casters

g. Pads

h. Direct Bury

Each of these support types may also have variations

Vertical Vessel Components

The pressure containment elements of the vessel are based of the process requirements for pressure,

temperature, commodity, corrosion rate, plant life criteria, and the applicable Codes.

The Pressure containment components include the following:

a) Shell

b) Heads

c) Boot

d) Transitions (Coke Bottle Vessels)

e) Nozzles

The other components include the following:

a) Trays

b) Internal piping

c) Support

d) Load Handling Devices

e) Pipe supports and Guides


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f) Platforms, Ladders, and Cages

g) Code Name Plate

Vertical Vessel Terminology

Normally vessel components are described using common terms such as shell, head, nozzle, and

support. Some vessels will also have special terms based on function.

Typical special terms include the following:

a) Flash Section -- The area or zone of the fractionation vessel where the primary feed enters the vessel.

b) Fractionation Section -- The portion of the vessel that includes the trays.

c) Stripping Section -- A place in the vessel that includes the introduction of supplementary heat such as

high temperature steam

d) Surge Section -- The bottom portion of the vessel that normally includes the main outlet nozzle which

is connected to the bottoms pumps.

Shell

The shell of the vertical trayed vessel will have many variables including the following:

a) Wall thickness

b) Metallurgy (May have different material at top vs. bottom)

c) Layers (single layer vs. multiple layer or cladding)

d) PWHT (Post weld heat treat) requirements for all or part

e) Vacuum reinforcement rings

f) Insulation support rings

Heads -- Top and Bottom

Heads for vessels will include the following shapes:

a) Dished -- The Dished head is a flatter version of the Semi-Elliptical

b) Semi-Elliptical -- The traditional type used on process plant pressure vessels (2:1 SE Head)

c) Spherical -- This head is sometimes referred to as a round head or Hemispherical-head

The top head and the bottom head may be the same shape but they will have some differences.

The differences for the top head include:


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a) Same material as top of Shell

b) May be thicker material for reinforcing

c) May be thinner material

The differences for the bottom head include:

a) Same material as bottom of Shell

b) May be thicker material for reinforcing

c) May be thinner material

Transitions

The cone or transition piece for regular and inverted Coke Bottle vessels may come in the following

shapes:

Flat side -- The cone is cut from flat plate and formed to a simple cone. There is no knuckle radius at the

top or bottom of the cone. The connection to the straight shell of the vessel is an angled weld. Usually

there is a reinforcing ring on the shell very close to the shell/cone junction.

Shaped side -- The cone is cut from flat plate and rolled to a shaped cone. There is a knuckle radius at

the top and bottom of the cone. The cone has a straight tangent at the top and bottom to match the

shells. The connection to the straight shell of the vessel is a common butt weld.

Nozzles

Overhead Vapor Outlet Nozzles

The overhead vapor outlet nozzles on a vertical vessel can have some latitude when it comes to

attachment location. The attachment connection can be direct to the top head of the vessel or may be

from the side. When the connection is from the side there will normally be a pipe inside the vessel

angled up to the top head area. Small vapor outlet nozzles from small diameter vessels can be located

out the side of the vessel and still be cost effective. Large diameter vapor outlet nozzles on large

diameter vessels will be more cost effective if attached to the top head. The line is then looped over to

the selected pipe drop position to go down the vessel.

Heater/Vessel Feed Transfer (Feed Inlet) Nozzles

All vertical fractionation vessels will have a feed inlet nozzle. This feed nozzle is special and critical on

some vessels. Refinery Crude columns and Vacuum columns are examples that have this type of nozzle.

This nozzle installation is characterized by the following:

a) Attached line originated at a fired heater

b) High temperature


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c) High velocity

d) Mixed phase flow

e) May require internals such as a distributor pipe or impingement plate

A Feed Transfer nozzle will normally be the "Key" (Genesis) nozzle for any large fractionation vessel.

Normally any side inlet orientation is possible but in most cases this will then dictate the tray

orientation.

Liquid (secondary) Inlet Nozzles

A normal liquid feed nozzle will not have the same complexities as the Feed Transfer type. This nozzle

installation is characterized by the following:

a) Attached line originated at an exchanger

b) Hot but not overly high on the temperature scale

c) Some may have potential for mixed phase flow

d) Normal line velocity

e) May require vessel internals such as a distributor or inlet pipe

f) Watch Instrument connections in relationship to Inlets and reboiler returns.

Reflux Nozzles

A normal reflux nozzle will not have the same complexities as other nozzles.


a) Attached line originated at a pump

b) Low on the temperature scale

c) All liquid flow

d) Normal line velocity

e) May require internals such as a distributor or inlet pipe. Multiple pass trays will require a morecomplex distributor or inlet pipe than a single pass.

Draw-Off Nozzles

The purpose of this nozzle is to draw-off or remove the primary product. They are also used to Draw-off

a secondary product to side stream stripper. May be installed with a sump to remove unwanted water in

the process stream.


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a) Located in the downcomer area of the column

b) May be in a sump

c) May be a larger size than the normal attached line size (Some of the initial vertical drop will be the

larger size)d) All liquid flow

e) Normal line velocity May require internals if multiple pass trays

Bottom Reboiler Feed Nozzles

The liquid outlet nozzle will normally be in the center of the bottom vessel head.


a) Located in the bottom of the surge section of the column

b) May be a very large size and all liquid flowc) Normally very low line velocity

Side Reboiler Feed Nozzles

This is also a potential Key Nozzle. The liquid outlet nozzle must be oriented in the same quadrant as the

bottom downcomer.


d) Located in the downcomer area of the column

e) Will be in a sumpf) May be a larger size than the normal attached line size (Some of the initial vertical drop will be the

larger size)

g) All liquid flow

h) Normal line velocity

i) Relationship to elevation of associated Reboiler is critical to nozzle elevation and internals

Side Reboiler Vapor Return Nozzles

One of the primary issues with this nozzle is the orientation relative to the other internal items and

nozzles. If not placed in the right place the velocity of the return can blow liquid out of a seal pan or can

affect the readings of any instruments attached to the far wall.


a) Attached line originated at a thermo-siphon or kettle type reboiler

b) High temperature

c) Moderately high velocity


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d) All vapor flow

e) May require internals such as a pipe or impingement plate

f) Relationship to elevation of associated Reboiler is critical to nozzle elevation and internals

Bottoms Out and Drain Nozzles

The bottoms-out nozzle is normally a pump suction source. The standard type is located in the bottom

head then piped through the skirt with a drain nozzle off the bottom out line nozzle. This would be a

combination nozzle. A variation of the bottoms nozzle is the siphon or winter type. This type may be

used (with process approval) when bottom clearance is a problem.

Note: It is common industry practice to avoid locating any flanged connections inside the vessel support

skirt. All flanges are subject to leaks, and vessel skirts are classified as a confined space.

Level Instrument Nozzles

Extreme care must be used when locating level instrument nozzles. There are access and clearances

problems that must be considered on the outside of the vessel. There are sensing location and

turbulence problems associated with the inside of the vessel.

These nozzle installations are characterized by the following:

a) Must be attached in the same pressure volume of the vessel

b) Lower nozzle in liquid of the surge section, upper nozzle in vapor space

c) Located in static area (or with stilling well)

d) Requires external access for operation and maintenance

Pressure Instrument Nozzles

Pressure readings are normally taken in the vapor area of a vessel. Pressure connections shall be located

in the top head area, 3" to 6" under a tray, or well above any liquid level in bottom section.


a) Located in a vapor space of the vessel

b) Requires external access for operation and maintenance

Temperature Instrument Nozzles

Temperature readings are normally taken in the liquid area of a vessel. Temperature connections shall

be located 2" to 3" above the top surface of a tray, in the downcomer, or well below any liquid level in

bottom section.



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a) Located in liquid in the downcomer area

b) Requires external access for operation and maintenance

c) Interference with internals

Vapor temperature readings may be required for some situations. When required the preferred location

is in the downcomer area half way between the two trays.

Tangential or Hillside connections may be required due to the thermowell length or to accommodate

access from the ladder and platform arrangement. With the Process Engineer's approval investigate the

possibility of raising or lowering the temperature point one tray for better ladder and platform

arrangement.

Steam-Out Nozzles

Process plant vessels that contain hydrocarbon or other volatile fluids or vapors will normally have a

Steam-Out Nozzle. This nozzle has a number of options such as:

a) A simple blind flanged valve on the nozzle -- After the plant is shut down by Operations, the

maintenance group would remove the blind flange from the valve. They then attach a temporary flange

fitted with a hose coupling and proceed to steam out the vessel by connecting a hose from a utility

station.

b) A blind flanged valve and hard piped steam line configured with a steam block valve and a swing ell.

c) A fully hard piped connection from a steam source. This method would have double block valves, a

bleed, and a spec blind for positive shutoff.

The vessel steam-out nozzle should be located near the surge section (bottom) Manhole on vertical

vessels.

Manholes

Manholes are also considered a nozzle. They just do not have any pipe attached to them. They are

however, a very complex piece of the vessel orientation puzzle. The types of manholes normally relate

to the method of cover handling provided.

Manholes come in the following types:

a) With Hinge -- A Manhole may be hinged for side mount, for top mount, or for bottom mount

b) With Davit -- A Manhole may have davits for side mount or top mount only

c) Plain -- A Plain Manhole may be for side mount, for top mount, or for bottom mount

The manhole orientation in top or non-trayed section of a vertical vessel is somewhat flexible. Normally

any orientation is possible; however, the orientation of the manhole should be checked to insure that

the entry path is not blocked by any internals.


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The Manhole may be located in the top head on large diameter vessels if there is a platform that is

required for other items. Top Manholes on large diameter vessels have their built in good points and

bad points. The good point is that during shutdown the open manhole provides for better venting. It

also allows for a straight method for removal and reinstallation of the trays. The bad point is that ladder

access must be provided down to the top tray, and the manhole is competing with the other nozzles for

the space on the vessel head.

Orientation for manholes that are located in the trayed section of the vessel is more complicated. The

location of between the tray manholes has a number of restrictions. These restrictions include the type

of trays and the tray spacing. The first choice for the location of a manhole is between the down comers.

The last choice is in the downcomer space, but behind the downcomer. The downcomer would be fitted

with a removable panel to allow further access into the vessel. The location to be avoided is above a

downcomer where there is the potential for falling down in the downcomer space and injury. It would

be better to seek approval to move the manhole up or down one tray than placement over a

downcomer.

Manhole orientation in the surge section of a vessel is not as restrictive. The surge section of a vessel is

the bottom portion that, during operation will contain a large volume of liquid. Any orientation is

possible for a manhole in this section. However, the location of all manholes should be in the back half

of the vessel away from the pipeway. The surge section may have a large baffle plate bisecting the

diameter of the vessel and extending vertically many feet. A removable plate or hatch may be installed

in this baffle (by vessels) to allow access to the far side. The vessel orientation of the manhole should

not hit the baffle or be located so close to the baffle that entrance is obstructed.

Trays

The type of trays, the number of trays, and the number of passes are not the specific responsibility of

the piping layout designer. However, there is the need to know factor. A common understanding of

terminology will improve communications and prevent errors. The common tray parts are:

a) Tray (support) Ring -- The tray support ring (or Tray ledge) is technically not a part of the tray itself.

The tray support ring is only there to support the tray. If there are no trays, then there is no need for

tray support rings, therefore tray rings are linked to the trays. Tray support rings are normally a simple

donut shaped strip welded to the inside of the vessel. They could also be in the shape of an inverted "L"

welded to the vessel wall. Problems arise when the Designer does not allow for the tray support device.

b) Trays (or Tray Deck) -- One or more sections, consisting of plates, forming a horizontal obstruction

throughout all or part of the vessel cross section. The trays will normally be constructed to form flow

patterns (one or more) called passes. The purpose of tray deck is to provide a flow path for the process

commodity and contain the fractionation or separation device.

c) Weir -- A low dam (on a tray) to maintain a liquid level on the tray

d) Downcomer -- The primary liquid passage area from one (higher) tray to another (lower) tray


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e) Valves -- Tray hardware device

f) Bubble Caps -- Tray hardware device

g) Draw off - A way to remove liquid from the vessel

h) Trough - A way to collect and move liquid from one point to another

i) Riser - A device to channel vapor from one lower point to a higher point

j) Seal Pans - A device (with a liquid seal) that prevents vapors from passing

k) Beams & Trestles - Devices that support trays (or other types of internals) in very large diameter

vessels

l) Baffles - A separation device inside a vessel

m) Chimneys - (See Riser)

Tray Pass Patterns

The trays and the related down comers can be arranged in a wide verity of patterns.

Typical Tray arrangements are:

a) Cross Flow, Single Pass -- (Common) this tray pass arrangement has one feed point, one flow

direction, and one downcomer. The single pass tray will normally be used on small diameter vessels and

the smaller diameter of a Coke Bottle vessel.

b) Cross-Flow, Multiple Pass -- (Common) the multiple pass trays will come in two pass, three pass, four

pass, and on and on. These will normally be found in the larger diameter vessels. Multiple pass trays

require multiple feed and draw off arrangements. The more passes, the more complex the orientation

problems.

c) Reverse Flow, Single Pass -- (Rare)

d) Radial Flow -- (Rare)

e) Circumferential Flow -- (Rare)

f) Cascade Flow -- (Rare)

The single pass tray will have a single downcomer. The 2, 3, or 4-pass tray will have the same number of

down comers as passes. The number of passes (number of down comers) will have a big effect on the

orientation. Some towers may have more than one Tray pass configuration. They may have single pass

in the top Trays and two-pass Trays in the bottom. The change from one pass configuration to another is

chance for error. The alignment of the single pass tray will normally be perpendicular to the two pass

trays.

Tray Types

There is what would be considered "Standard" Trays, and there are also "High efficiency Trays".

a) "Standard" Trays -- This tray will have an open downcomer with no separation occurring in the

downcomer area. This tray is the old stand-by and has been used for many, many years.

b) "High efficiency Trays" -- This tray will have a sealed downcomer with separation occurring in the


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Some other terms that will be found relating to trays.

a) Sump -- This is a sealed downcomer type area that is designed to provide a retention volume for some

purpose.

b) Seal Pans -- This is a portion of a tray that is set deeper than the rest of the tray to form a seal for the

downcomer from the tray above.

c) Side Draw Tray -- A tray arrangement that allows the removal of a specific liquid product

d) Chimney Tray -- A full circumference tray fitted with long open pipes to allow vapor to pass from

below the tray to the space above.

e) Baffles -- Plates installed in the vessel for a specific purpose

f) Impingement Plates -- Somewhat like a baffle but normally a plate installed in the vessel at the inlet to

prevent blowout to devices located on the opposite side of the vessel.

g) Tray manholes -- Most, if not all, trays will have a removable panel (somewhere in the tray) to allow

inspection passage without dismantling the total tray

Vessel Support

The method of vessel support depends on various factors. These factors include process function,

operation access, maintenance clearances, ease of constructability, and cost. Meeting the positive

criteria for all or the majority of these factors will drive the support method.

The primary methods of support are:

a) Tall Skirt on foundation at grade (Most common)

b) Short Skirt on elevated pier foundation, table support, or structure

c) Legs on foundation at grade

d) Lugs on elevated pier foundation, table support, or structure

Each of these vessel support methods has their own good points and bad points. The Tall Skirt is the

most common because it meets more of the "preferred criteria" than the others do.

Skirt Vessel Support

The minimum height of the skirt is normally set by process based on the NPSH requirements of the

pumps or for the reboiler hydraulic requirements. The designer may need to increase the skirt height

due to:

a) Vertical distance required by pump suction line geometry

b) Vertical distance required by reboiler line geometry

c) Operator aisle headroom clearance

d) Suction line entering the pipe rack without pockets

The approval of the Process engineer, Project Manager, and the Client will be required for any increase


29/47

to the skirt height.

The skirt will have one or more access openings and will have skirt vents.

Skirts of vessels in refineries or other plants processing flammable commodities will normally be

fireproofed. The fireproofing is normally a two-inch (2") thick layer of a concrete type material applied

to the outside of the skirt. Check for the specific type. Some materials may require up to 6" to obtain the

required fire rating.

Load Handling Devices

Load handling devices are required for Vertical Vessels if:

a) The vessel is over thirty feet (30') tall

b) The vessel has removable trays and internals

c) The vessel has components that require frequent removal for routine maintenance (PSV, control

valves)

d) The components weigh 100 pounds or more

Methods of load handling include:

a) Davit -- A small somewhat inexpensive device used for lifting and supporting heavy objects up and

down from elevated platforms. Limited to a fixed reach.

b) Monorail -- A more expensive method

c) Crane -- A far more expensive method and is dependent on availability

If a davit or monorail is not installed then a crane with the required reach and load rating must be

rented or an alternate method must be jury-rigged. Any jury-rig method will have a high potential for

accident and injury.

When a Davit is to be included the following must be determined and furnished to Vessels:

a) The location

b) The swing

c) The clearance height (including lifting device)

d) The reach - the removal items (e.g... PSV, Control Valve, Block Valve, Blinds, etc.) and the drop zone

e) The maximum load of external items (Vessels will determine weight of internals)

When a Monorail is to be included the following must be determined and furnished to the Vessels

engineer:

a) The platform, and monorail support configuration

b) The clearance height (including lifting device)

c) The reach to the drop zone


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d) The maximum load of external items (Vessels will determine weight of internals)

Pipe Supports and Pipe Guides

The Pipe Supports and Pipe Guides (PS & PG) for the piping that is attached to the vessel is the

responsibility of the Piping Group. You're the Piper, that's pipe, and you need to make sure it is properly

supported and guided. The rule is (or should be) that all lines shall be properly supported and guided.

One key element of the PS & PG is the "L" dimension. The "L" dimension is the distance from the O. D. of

the back side of the pipe to the O. D. of the vessel. This dimension should be as small as possible but not

less than required for maintenance. The rule of thumb for the "L" dimension is 12" minimum and 20"

maximum. Dimensions of under the 12" and over the 20" are sometimes allowed. For example, if fitting

make up results in an "L" dimension of 11 13/16" do not add a spool piece and extra weld.

Lines should be supported as close to the nozzle as possible. The type of support is based on the weight

of what is being supported. It may be just a straight pipe dropping down the side of the vessel. Or, it

may be much more.

The requirements for pipe supports attached to a vessel must be evaluated for the following:

a) The shell thickness

b) Orientation

c) Elevation

d) The "L" dimension

e) The weight of the basic pipe and fittings (based on size and wall schedule)

f) The weight of the water during hydro test

g) The weight of the insulation (if any)

h) The weight of any added components (block valves, control valve stations, relief valves, etc.)

i) The clearance to other objects (Seams, Stiffener rings, Nozzles, Clips, Pipe Lines, Platforms)

The requirements for pipe guides attached to a vessel must be evaluated for the following:

a) The shell thickness

b) Orientation

c) Elevation

d) The "L" dimension

e) The size of the line at the point of guiding

f) The distance above the horizontal turn out (allow 25 pipe diameters +/-)

g) The maximum allowable span between guides

h) The clearance to other objects (Seams, Stiffener rings, Nozzles, Clips, Pipe Lines, Platforms)

Pipe supports and guides should be staggered vertically for clearance from supports or guides on other

lines running parallel.

Platforms, Ladders, and Cages

Platforms with access ladders must be provided as required for access to manholes, operating valves,

and instruments as defined in the project criteria. Normally objects below 15' - 0" from grade will not


31/47

require permanent platforms and ladders. These objects are judged assessable by portable means

(Check the Project design requirements).

Platform spacing shall be even foot increments when multiple platforms are serviced from a single

ladder. The platforms shall be arranged to allow the following:

a) Minimum 7' - 0" headroom to underside of any obstruction

b) Minimum 2' - 6" radial width for primary egress path (I. D. of platform to O. D. of platform)

c) Minimum 2' - 6" clear distance between ladders

d) No obstructions in path between primary egress ladders

e) Maximum 30' - 0" vertical travel length of ladder between platforms

f) Side step off at all platforms (Step through ladders are considered dangerous and therefore should be

avoided). This requirement should have been reviewed with the Client and defined in the Design

Criteria.

g) Combining with platforms on other vessels when potential for improved operations or maintenance

exists

h) Flanges of top head nozzles shall be extended to provide access to bolts

i) Minimum 1' - 6" clearance around objects if for maintenance access only

Code Name Plate

Every vessel will have a Code Name Plate. On a vertical vessel the code name plate must be on the

(pressure containment) part of the shell. It cannot be attached to the skirt. The best place for the code

name plate on a vertical vessel is 2' - 6" above the horizontal centerline of the surge section manhole.

Make sure the location selected is accessible on grade or on a platform.

Common problems with vertical vessels

a. Schedule crunch - Vessels scheduled for purchase too early requiring firm orientations with very little

backup information.

- Approved and Issued for Design P&IDs

- Exchanger type and location

- Flare header and PSV location

b. Thin wall vessels not able to support load on pipe supports

c. High wind presence requiring extra guides

d. Late changes to PSV sizing prompting changes to pipe support and guides on line to flare

e. Late change to control valve location criteria (Flashing service now required to be located to elevated

platform on vessel with line downstream of valve self drain to vessel)

f. Reboilers requiring spring mounted supports due to tight piping and differential growth

g. High steam-out temperature requiring extra flexibility in the piping

h. Extra heavy object removal in excess of Davit load capabilities

Vertical Vessel Orientation

Recommendations


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behind the ladders. Do not route small lines vertically between the vessel shell and the inside radius of

the platforms. Do not route small lines vertically up the outside of the platforms in line with or close to

the manholes.

k. Ladder access openings must be fitted with a safety gate. Check for proper clearance for gate swing.

l. Some processes are subject to periods of hazardous operations. Ladders and ladder cages may need to

be designed for operators with self-contained suits and air packs (SCBA).

Skirts

a. The minimum skirt height is set by Process and indicated on the P&ID.

b. The skirt height is normally based on the minimum NPSH of the bottom pumps.

c. The skirt height may be influenced by the physical requirement of a thermo-siphon reboiler.

d. The final skirt height needs to consider and be adjusted for; physical configuration of the bottoms

nozzle, any headroom clearance required over operating aisles, vertical fitting geometry of the piping

configuration, and the pump suction nozzle location.

e. As a general rule no flanged connections are allowed inside the skirt of a vessel. This area is

considered a confined space in most plants and flanges will tend to leak over time.

f. Increasing the Skirt height may be considered when adjacent vessels warrant lining up and connecting

platforms.

Reboilers

a. Reboilers will be one of the following; Fired (Heater Type), Thermosiphon (vertical or horizontal shell

& tube), or Kettle type (horizontal shell & tube).

b. Fired Reboilers shall be located a minimum of fifty feet from the vessel.

c. Piping to and from any type of reboiler will be hot, and have sensitive flow conditions.

d. The Kettle or Thermosiphon Reboiler elevation is set by Process and indicated on the P&ID.

Pipe Supports and Guides

a. Piping is responsible for locating the pipe supports and guides on vessels

b. Piping is responsible for defining the size and loads on the pipe supports on vessels

Piping Flexibility

a. Piping must determine the operating thermal growth of the vessel. The vessel will have a series of

temperature zones from the bottom to the top.

b. The differential expansion between the piping risers and the vessel must be checked to prevent over

stressing the piping or the vessel shell.

c. The routing of cooler reflux lines must consider the total growth of the hotter vessel.

d. Potential for differential settlement needs to be investigated

e. Each piping system or line needs to be considered individually

Instrumentation

a. The HLL, NLL, and LLL need to be carefully considered because they will set the elevations of the level

instruments


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b. Orientation of level instrument connections needs to consider the internals

c. All instruments shall be accessible

d. Watch out for space requirements for gage glass illuminators.

e. TI and TW connections will require removal space

Electrical

a. Space shall be allocated for conduit runs up the vessel. These conduits will carry power to platform

lights, gage glass illuminators, and in some cases electrical tracing.

b. Conduits are also required for controls (instrumentation)

Piping Valves

a. Valves are meant to be operated and to be operated they must be accessible.

b. Small valves (2" & smaller) may be considered accessible from a platform or ladder. Large valves (3" &

larger) shall be accessible on a platform.

Misc. Piping issues

a. Lines to and from vessels may be subject to conditions such as 2-phase flow or vacuum.

b. Some PSV relieving to atmosphere will require snuffing steam. The steam pressure (in the line) must

be adequate to reach the top of the vessel.

c. Large overhead lines vs. PSV location require special attention for function and support.

d. Vertical vessel piping needs to be checked for heat tracing requirements. A tracer supply manifold

may need to be added at the top of the vessel.

Constructability

All vertical vessels shall be reviewed for constructability. This review needs to consider receiving logistics

lay down orientation, lifting plan, pre-lift assembly items (piping, platforms, ladders, internals, etc.)

- Pre-lift assembly items may include the following:

a. Piping

b. Platforms

c. Ladders

d. Internals

e. Paint

f. Insulation

Fire Protection

a. Some vessels may require special insulation for fire protection.

b. Some vessels may require fire monitor coverage

c. Some vessels may require sprinkler systems

Misc.

Some vessels will be lined. Linings may be metallic, plastic, or glass. Welding to the vessel shell after

initial fabrication is not allowed.


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Some vessels will have flanged connections that are larger than 24". These connections will occur at

connections for piping, reboilers, or other equipment. Flanged connections over 24" do not have a single

standard and need to be defined for specific type (API or MSS).

(BACK TO TOP)

Section - II

C-II: Vertical Vessel Orientation


The following article was prompted by questions from a young piping designer. He wrote:

-------------------------------------------

Hi

I am getting ready to do my first vessel nozzle orientation. The vessel is a Stripper Tower (a). Can you

help me? First, what are the things I have to take into consideration? Second, what are the key steps in

the process for doing a vessel nozzle orientation?

Regards

XXXXXXXXXXXX

---------------------------------------------

(a)The name/function of the vessel has been changed.

For your first question: "What are the things I have to take into consideration?"

The answer to this question is very simple; you must take everything in to consideration. Everything is

important! Someone may tell you that some things do not matter but this is not true, everything

matters.

You need to consider the following:

a) Timing: Vessel orientation is normally the only equipment related layout activity that can be done

without specific input from a vendor. All of the information required for vessel orientation is generated

on the project in the form of P&ID data and project standards. It is also one of the few activities that will

feed one or more other downstream groups whose work is critical to the project schedule. With this in

mind this activity can and should be started as soon as the P&ID reaches "Approved-For-Design" (AFD)

status. Te vessel orientation activity can be started manually or on basic 2D CAD before the 3D PDS data


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base is fully loaded and checked. There is some logic to doing this activity manually or in 2D CAD

because of the amount of trial and error required to finally achieve an acceptable and approved

orientation. Once the orientation is approved and the PDS data base is ready the 3D model can be built

with no recycle.

b) The Plot Plan (Note 1): The plot plan is required to identify the location of the vessel and its relatedequipment. The related equipment includes the equipment that feeds the vessel (is up-stream) and also

the equipment that the vessel feeds (is down-stream). It shows and locates adjacent, non-related

equipment. It also shows adjacent structures that may support the related up-stream or down-stream

equipment. It also indicates the plant features such as pipe racks, operating aisles, maintenance access

areas and the direction of Plant North.

c) The project foundation criteria: Vertical vessels normally sit on an octagon pad foundation with the

top of grout at EL101' - 0" (high point of finished paving = EL 100' - 0"). You need to have and

understand the type and elevation of the foundation for this vessel.

d) The P&ID's (Note 1): The P&ID's are required to show the process streams that connect to the

Stripper Tower and its related equipment. In my experience P&ID's are much like the pages in a book.

Some equipment (the heater) starts or shows on sheet one P&ID the story continues with the key item

(the Stripper Tower, Thermosyphon Reboiler and Bottoms Pumps) showing on sheet two and then

continues to some conclusion (the overhead condensers) on sheet three. You will need all three process

system P&ID's. The Stripper Tower P&ID will show a graphic of the column along with all the piping

connecting to the vessel. There will also be a data block at the top of the page. This data block should

include the vessel number, the vessel name and the basic size. It will also indicate the design

temperature and the insulation requirements (if any). The graphic of the vessel should also indicate the

basic type of internals (Trays or Packing). If the internals are Trays then the number of trays should be

indicated. The trays just above or just below where a line is connected should be numbered. If the

internals are some form of packing then the extent of the packing beds should be indicated.

e) The project Line List (Note 1): The line List is required to give you specific and critical key data about

the lines such as the Line Number, line class, maximum operating temperature and insulation

requirements,

f) The project Piping Material Specifications (Note 1): The Piping Material Specifications are required to

give you the data about metallurgy and any specifics about fittings, flanges, valves or requirements for

PWHT (post weld heat treatment).

g) The Vessel Drawing (Note 2): The vessel drawing at this time will most likely be marked "Preliminary."

It will give you; the inside diameter (I.D.), the tangent-to-tangent shell length, the shape of the top and

bottom heads and the skirt height. This drawing should also have a table showing all the nozzles with

the basic information such as: identification, quantity, and size, flange rating, the elevation above (or

below) the bottom tangent line for each nozzle, the purpose for the nozzle and any special instructions.

The vessel drawing needs to also indicate where the internals start and end inside the vessel.


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h) The Internals (Note 2) (Trays or Packing) A tower can have a number of different types and

configurations of internals. It may be Trays or it may be some form of Packing.

- Trays: If you have Trays then you need to know: the number of trays, the spacing of the trays, the

number of passes for the trays (1-pass, 2-pass, 3-pass etc.). You also need to know if there are any "draw

sumps," baffles or other special features.

- Packing: You need to know the number of "Beds," the depth of the beds and the method of installing

and removing the packing material. You also need to know and understand about the type of feed

distributor(s) to be used. You need to know about the packing discharge nozzles.

For the purpose of this article we will assume we have 35 single pass trays.

i) The Thermosiphon Reboiler data sheet (Note 1): This will give you the preliminary size and type

information. The P&ID indicates that this vessel has a vertical Thermosiphon reboiler fitted to it. Some

discussion should normally take place to determine the optimum tube length and the proper support

elevation and support method.

j) The project Vessel Platform Standards (Note 1): This will give you the required information about the

minimum vertical spacing between platforms. It will also give you specific details about platform

supports and how to make the openings where pipes must pass through a platform. This drawing will (or

should) also give you specifics about handrails.

k) The project Vessel Ladder Standards (Note 1): This drawing will give you all the required information

about ladder construction and more important the limits for the maximum vertical run for a single

ladder.

l) The project Vessel Nozzle Standards (Note 1): This will give you all the normal options for un-reinforced and reinforced nozzles. It may also show you some options for internal nozzle piping.

m) The project Vessel Davit Standards (Note 1): A davit is a small device permanently mounted on the

vessel that acts as a crane for lifting heavy objects such as tray sections.

n) The project Vessel Pipe Support and Guide Standards (Note 1): These are devices attached to a vessel

that support and/or guide the vertical runs of pipe. This drawing also defines the minimum distance

from the outside of a vessel shell to the back of an adjacent pipe. Where I came from this was called the

"L" dimension. The "L" dimension was normally 12" (adjusted as required for insulation) The maximum

was 20" without a special design. The key was to have a minimum of 7" clear between two co-existing

insulations. These supports and guides also require a wider than normal line spacing in the vertical plane

as the lines go up or down a vessel. This is mainly due to the configuration of the Trunnion (Note 3)

support attached to the pipe and the pipe clamp used for the guide.

o) The project Piping and Vessel Insulation Specification (Note 1): From this document you will get the

thickness of the insulation needed for the pipes and vessel at the operating temperature.


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(Note 1): These items are normally created by your company for the project and should be "Approved

for Design" (AFD) quality documents. This means that they have been through all of the proper in-house

reviews and checks and have then been approved by the Company and the Client for use in the design

of the work.

(Note 2): These documents will initially come from the project Vessel Engineer. They will normally bemarked "Preliminary" until they receive and process your orientation drawings. Later you may receive

the vessel fabricator's detail drawings for "Squad Check" (review and approval).

(Note 3) For more information about a Trunnion support see www.pipingdesigners.com look under

Training and Secondary Pipe Supports

There may be other documents that are required due to a specific company's method of operation.

The next things you need to consider is; functionality, safety, operation, maintenance and

constructability.

Functionality: No matter what, this vessel must do its job. You must know and understand what that

intended job is. You do not need to be a process engineer but you should be involved in the review of

the P&ID for this specific vessel. You need to hear what the critical issues are relating to this vessel and

the connected piping. If your company does not include piping in the formal review of the P&ID's then

you need to seek out the process engineer and ask him or her to explain the function, key points and

any critical issues relating to this vessel.

Safety: This is the other important issue relating to vessel orientation. The operation must be able to be

done in a safe manner. The same must be said for both maintenance and constructability. To achieve

this goal the locations of nozzles relative to the placement and arrangement of the ladders and

platforms must be carefully considered. The travel path (access and egress) must be arranged so the

main travel path cannot be blocked by open manholes, scaffolding, tools, tray parts, valves or piping.

The basic rule here; a: ladder #1 comes up with a side step-off (right or left) on to platform #1. Then b:

there is a minimum rest space equal to one ladder width. Then c: the next ladder (#2) continues up to

the next platform. Platform #1 can continue beyond ladder #2 around the vessel to provide access to

nozzles and manholes. This arrangement does not impede or obstruct the clear path for rapid escape

from the vessel for anyone from a higher elevation. Other safety issues include one or more skirt access

openings located near grade which should be located with clear access. There will also be four or more

skirt vents located high near the skirt-to-vessel attachment which also should not be blocked.

Operation: Process plants need to be operated. Most operation is concentrated around valves andinstruments. These items must be accessible. Accessible means reachable. This reachable is conditional.

Nozzles with a nominal size of 2' (NPS) and smaller can be reachable from a ladder or from a platform.

Nozzles 3" (NPS) and larger shall be reachable on a platform. In this context the from means that the

object is not more than 18" (one arms length) from the ladder or platform and the on means the object

must be fully inside the platform. There is normally only one exception to this rule. That is for valves or

nozzles that are located less than 20 feet from grade and can be accessed w

Documents

Section II - Equipment Piping and Assembly Applications