Packing of control valves Presentation

Gland Packing of Control Valves

Presented by: Muhammad Asim

CONTENTS

• Introduction to Packing

• Types of Packing

• Packing Material Consideration

• Packing Configurations

• Packing Procedure

• Common Mistakes in Packing

• Packing Configuration of Critical Valves

• Incidents of gland packing failures and its consequences

What is Gland Packing?

• Any soft material encased in bonnet or body

used to seal a valve stem or shaft is called

Packing.

• Packing held in place by a Packing Follower

with compression supplied by Gland/Packing

Flange.

• Packing follower is a metallic ring used to retain

packing inside bonnet or body and to compress

the packing in uniform manner.

• Gland flange is a rectangular metallic block

connected to valve body through bolting.

• When bolting is tightened the gland flange –

through packing follower- transfers an axial load

to the packing, compressing the packing until a

seal is created against stem and bonnet bore.

• The configuration of packing, packing follower,

gland flange, studs is called PACKING BOX.

What is Lantern ring?

• A lantern ring is an annular ring with channels for

the passage of water that is inserted between the

gland packing. Fluid is fed from an external pipe

to the lantern ring for lubrication OR cooling of

the stem/packings.

• It is used in applications where a number of

packings are there and it would be difficult for the

intermediate packing to get fluid for lubrication.

• It is also used where the fluid to be sealed is

contaminated with abrasives or is corrosive and a

clean fluid is required for lubrication.

• While installation it is crucial that the holes in the

lantern ring meet or are aligned with the holes in

the pipes.

• It is very important to inspect and align the

lantern ring during each overhaul of the valve.

Position of Lantern Ring

Loading of Packing Rings

• Depending on material packings

produce a unique deformation

when compression is applied.

• Applied axial load can result in

wide range of radial load.

• Ideally, when axial load is

applied, radial load should be

greatest in middle of packing set

where maximum seal occurs.

Loading of Packing Rings

Packing Types

Packing Types: Jam Style

• Packing is loaded by compressive force

exerted by packing follower. Only elasticity

in this system resides in the packing

material itself. This is called stationary or

jam style packing. Over time packing

material wears, the packing follower must

be re-compressed by carefully tightening

the packing nuts.

• Excessive torque will result in high valve

stem friction and premature packing failure.

• Proper remedy for a packing assembly that

leaks despite having been properly torque is

replacement, not further tightening.

Packing Types: Live Loading

• A metal spring is inserted in packing

assembly, so that the elasticity of the

springs helps to maintain an appropriate

amount of packing stress as the packing

material wears and ages. This is called live

loading.

• Two types of live loading;

a. A coil spring inside the bonnet used to

live-load the pacing.

b. Set of spring-steel washers known as

Belleville springs installed between

packing flange and follower. These

washers always stacked in opposite

pairs as shown in picture.

Packing Types: Live Loading

Packing lubricators

In packing applications requiring

external lubrication, a stem

packing lubricator may be

connected to the lubrication port

on the bonnet. This device uses

a long, threaded bolt as a piston

to push a quantity grease into

the packing assembly

Packing Material Considerations

Packing Material: PTFE

• PTFE is common and inexpensive packing material.

Generally used in V-rings.

• With combination of PTFE elasticity and and the

pressure energized design of v-rings, little compression

is needed to create long lasting seal.

• PTFE provides very little friction. Therefore allows

smooth stroking and minimum breakout force, necessary

to begin valve lift.

• PTFE is inert to many process fluids.

• PTFE can be used up to maximum 232 deg C

temperature.

Packing Material: PTFE

• Major disadvantage of PTFE is its limited temperature

range.

• Because its thermal expansion is 10 times to thermal

expansion of steel, PTFE is especially vulnerable to

thermal cycling, which can result in packing loss and

shorter life. As PTFE is heated by the process, it

expands throughout all available spaces, which may lead

to extrusion. As the temp drops, the packing returns to

its original volume minus the amount lost to extrusion.

Bcz of this loss, less force is exerted against stem or

bonnet wall and consequently leakage occur.

Packing Material: PTFE

• Another disadvantage of PTFE is its tendency to

consolidate over a period of time known as cold flow. It

occurs when packing is compressed several times or if live

loading is used. To prevent it, a backing or anti-extrusion

ring can be installed that will slow the process. A backing

ring is a close tolerance ring made from a harder less

pliable material and is inserted at top of packing to transfer

the axial force from gland flange to packing. In most cases

backing rings are installed at both ends of PTFE packing

and provide an exact fit between the ring and stem as well

as packing box wall. This exact fit is critical to preventing

the cold flow from extruding past the back up ring.

• Filled PTFE is similar to PTFE although it includes some

glass content to provide more rigid V-ring that is less likely

to consolidate.

Packing Material: Graphite

• Graphite is an expensive but high temp alternate to

PTFE for packing.

• Graphite can be produced in die formed rings and

braided rings.

• Die formed rings are produced from graphite ribbon,

which is wound and then compressed in a die according

to specified pressure. This pressure to form the rings is

less than the force required to compress the rings to seal

the packing box.

• Braided graphite is produced by winding small strands of

graphite together which makes it quite pliable as

compared to die formed rings. When used as sealing

packing, it forms so well to the stem that the resulting

stem friction impedes free movement of the stem.

Packing Material: Graphite

• Because of this problem, braided packing is used as an

anti-extrusion ring on both sides of the die formed rings.

• However, this may cause a problem when higher

compression is need, since braided graphite has the

tendency to grab the stem and not transfer the load to

die formed rings. Hence higher friction results from

braided packing, yet leakage may occur because

insufficient load is reaching the primary seal which is the

die formed rings.

Packing Material: Graphite

• Graphite packing offers number of advantages. Overall

graphite remains stable over a wide range of thermal

cycling, bcz its expansion is nearly equal to steel, it does

not extrude or loose seal in thermal cycles.

• Chief drawback of graphite is that when fully

compressed to provide effective seal, it has a tendency

to stick to the stem resulting in jerky valve motion or

premature wear of moving parts. This phenomena is

more sever in rotary valves as compared to linear

valves.

• Another major problem with graphite is that it is

extremely fragile and can be broken or crushed when

over compressed or over tightened. Using wrenches to

apply recommended torque is mandatory when installing

graphite packing.

Packing Material: Graphite

• Graphite packing also has the unfortunate property ofpermitting galvanic corrosion between the stem andbonnet metals due to its electrical conductivity. Sacrificialzinc washers are sometimes added to graphic packingassemblies to help mitigate this corrosion, but this onlypostpones rather than prevents corrosive damage to thestem.

• The packing manufacturer should be consulted todetermine whether the valve should be removed duringhydro testing. Graphite packing will corrode the stem ifleft wet.

• Graphite is fire safe which is important where firemigration is a concern.

PACKING CONFIGURATIONS

Packing Configuration, Single

• This is an economical seal for many applications. Single

packing consists of a stack of packing at the top of the

packing box supported by either a spring or gland

follower. Spring packing can be accomplished by having

the packing follower drawn against the bonnet to

compress the spring.

• PTFE: V-rings and braided packings can be used in

single packing configuration.

• Graphite: Combination of square and braided packing is

used in single configuration.

• Picture on next slide shows a single packing

arrangement using V-rings.

Single Packing Arrangement

Single packing arrangement using PTFE V-rings

• Double packing arrangements provide a more rugged

seal than single arrangements and generally have

packing above and below the lubricating/ lantern ring

connection.

• PTFE: V-rings and braided packings can be used in

double packing configuration.

• Graphite: Combination of square and braided packing

can be used in double configuration with lantern ring for

lubrication purpose. Lubrication keeps the graphite

packing soft and pliable while providing smooth valve

travel.

• Double packings are also used for vacuum and pressure

services.

Double packing arrangement using PTFE V-rings

Graphite packing is not as

resilient as PTFE packing

and any lateral movement of

the stem will enlarge the

packing bore, leading to

leakage. To prevent packing

damage and subsequent

leakage, carbon guide

bushings are located above

and below the packing rings

to provide stem guiding. The

guide bushings are made of a

nonmetallic material to

prevent scratching the stem.

• Packing consolidation is a reduction in packing volume due

to Wear, Cold Flow, Plastic Deformation and Extrusion.

• When packing is loaded to its proper stress level it has a

tendency to cold flow and will extrude between the stem

and the follower. PTFE has an expansion rate roughly ten

times that of carbon steel. As the temp rises, packing tries

to expand in the fixed volume of the stuffing box, extrusion

will occur. This material loss due to extrusion will relieve the

axial stress, which relaxes the radial stress and results in a

loss of seal.

• In most cases when consolidation occurs, the packing box

will begin to leak and the gland flange bolting must be

tightened further to seal the leakage.

• By virtue of its close proximity to process, packing

material can be affected by the process temp and press.

• As the Temperature increases, softer packing material

will become more fluid and are more apt to extrude out

of the packing box.

• High pressure can also cause extrusions.

• PTFE packing can be used up to 230 Deg C. For higher

temperature, graphite packing is used.

• Valve OEM manual must be consulted for recommended

packing material at specific temperature and pressure.

• Clean and inspect nut and bolts. The nut should be able

to smoothly travel the length of bolt. Test by finger

tightening.

• Always use hardened flat washers under gland nuts to

evenly distribute the torque to gland flange.

• Ensure packing gland follower can be inserted freely into

the stuffing box without interference.

• Make sure packing follower is seated evenly against the

packing.

• Measure the distance between gland flange and stuffing

box face to ensure evenness.

• Readjust gland nuts after the valve has been actuated a

minimum of five times with the valve in the closed stroke

position.

1. Trueness of the shaft. A shaft that is bent would eat the

gland packings prematurely and there nothing you can do

except change the shaft. You must make it a point to

check the trueness of the shaft during each overhaul

using a dial gauge.

2. Concentricity of the shaft with the stuffing box bore.

The shaft might be true but if not aligned properly would

again destroy the gland packings in no time.

3. Surface roughness of the shaft. If the shaft or the

sleeve is pitted or unevenly worn it would again damage

the gland packings very fast.

PROCEDURE FOR NEW PACKING

Videos of Packing Installation

• Installation of Braided Packing

• Installation of V-ring Packing

• Installation of Graphite Packing

Common Mistakes in Gland Packing

Common Mistakes in Gland Packing

• Uneven tightening of gland pusher

• Gland pusher at least 2-3 mm inside stuffing box

• Do not use reinforced braided packing (doori) on hydrogen

service

• Short bolting of gland nuts

• Lantern ring position

Packing configuration of critical valves

• 01-LRC-1V

• 01-LRC-2V

• 05-HIC-1V

• 05-LIC-5VA/B

• Braided packing provided

in twin configuration.

Lower packing has four

rings while upper packing

has 08 rings.

• Lantern ring is provided for

circulation of clean water

which takes away any

leaking fluid from lower

packing. Flushing water

will also serve as cooling

media for valve stem.

• Bushing is provided for

alignment of valve stem.

• V-rings provided in twin

configuration

(06+01+01+03).

• Lantern ring is provided for

circulation of clean water

which takes away any

leaking fluid from lower

packings. Flushing water will

also serve as cooling media

for valve stem.

• PTFE V-rings provided on both sides of Butterfly body.

05-FRC-3V

• V-rings provided in twinconfiguration (05+05).

• Spring is provided in betweencirculation of clean water whichtakes away any leaking fluid fromlower packings. Flushing waterwill also serve as cooling mediafor valve stem.

• Mettalic Anti-extrusion ringsprovided (Item # 17a, 23 inpicture) to prevent extrusion ofpacking rings.

05-LIC-5A/B

• V-rings provided in twin

configuration (05 + 05 reverse).

• Spring is provided in between

circulation of clean water which

takes away any leaking fluid

from lower packings. Flushing

water will also serve as cooling

media for valve stem.

• Mettalic Anti-extrusion rings

provided (Item # 17a, 23 in

picture) to prevent extrusion of

packing rings.

INCIDENTS OF PACKING

FAILURE

• Packing of 05-HIC-1V was failed in plantstartup in 2012 at Plant-I.

• Plant startup was halted and glands wererepacked in field.

• Valve was attended in workshop and its stemand gland packing were replaced.

• Cause: Gland follower outside stuffing boxdue to installation of additional braidedpacking (Doori) in addition to PTFE V-rings tocreate extra margin for future tightening infield..

Incident Report

On October 19, 2014 at 1740 hrs, excessive Synthesis

Gas leakage with a jet of approximately 8-10 ft was

observed from Ammonia reactor, R-501 inlet valve, 05-

HIC-1V east side gland packing (Non-actuator side).

In May, 2014 during startup of the plant, the leakage

from gland packing of 05-HIC-1V was observed (hand

felt). The leakage was arrested at that time by tightening

the gland packing. Based on May 2014 leakage

history/incident, the gland packing was attended during

turnaround 2014, by adding packing rings and tightening

of packing.

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