Prepare for the 4th Edition of API 682

7/27/2019 Prepare for the 4th Edition of API 682

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PREPARE FOR THE

4TH EDITION OF API

682This comprehensive international standard formechanical seal and system use has many important

changes.Originally published in the April 2012 issue of Pumps & Systems

After more than five years of planning, the American Petroleum Institute (API) is

preparing to release the 4th edition of API Standard 682 (ISO 21049:2011). The

API 682 standard, which dates back to 1994 and is formally known as Shaft

Sealing Systems for Centrifugal and Rotary Pumps, offers specifications and best

practices for mechanical seals and systems to pump end users.

The standards latest edition began to take shape in 2006, when API formed a 4th

edition task force to respond to end users questions and comments about previous

editions. The task force soon realized that major changes, including reorganization

and editing, would be necessary. While addressing every aspect of the resulting 4th

edition (which is more than 250 pages long) would be impossible, this article

summarizes the standards main points.

Those who use API 682 should understand the standards scope and remember thatthe standard does not include specifications for equipment outside that scope, such

as engineered seals or mixers. Another important but often misunderstood point is

that API 682s figures are illustrative and not normative in their entirety.

For example, one of API 682s figures shows a fixed throttle bushing combined

with a rotating Type A seal, but seal manufacturers do not always have to combine


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these two components. The standard provides normative details in clauses and

tables to help purchasers distinguish between requirements and suggestions.

Mechanical Seal and System Designs

The 4th edition continues to divide seals into three categories, three types and three

arrangements. For all practical purposes, seal manufacturers can combine a seals

component parts into nearly any orientation or configuration. Each orientation and

configuration has advantages and disadvantages with respect to certain

applications, performance and system disturbances.

Before the 4th edition, API 682 did not specify a minimum clearance between the

inside diameter of a stationary seal part and the outside diameter of a rotating seal

part. The 4th edition specifies this minimum clearancetypically the clearance

between the sleeve and the mating ring. The specified clearances are representative

of standard clearances that end users have used for decades. End users should not

consider seal components to be shaft catchers to restrict shaft movement. The

minimum clearance specified in API 682 also applies only to equipment within the

standards scope. Equipment outside that scope, such as non-cartridge seals, olderpumps, non-API 610 pumps and certain severe services, might benefit from larger

clearances.

The new standard also updates the default bushings for the gland plate for the three

seal categories. Fixed throttle bushings are now the default for Category 1 only,

while floating bushings are the default for Categories 2 and 3.

Seal Selection ProcedureWhile the 4th edition features the recommended seal selection procedure from the

standards first three editions, it adds an alternative selection method in Annex A.

Proposed by task force member Michael Goodrich, this alternative method

recommends using material data sheet information to select a sealing arrangement.


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The 4th edition of API 682 provides specifications for piping plans such as the one

shown here, Plan 53C.

Seal Codes

Once again, seal codes have changed. The new code, described in Annex D, is

probably the best to date. It uses eight fields:

Seal category Seal arrangement Seal type Containment device Gasket material Face material Approximate shaft size (in millimeters) Piping plan


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For example, based on the 4th edition codes, a seal code of 31B-LIN-075-53A

indicates:

3 Category 3 seal 1 Arrangement 1 seal B Type B seal L Floating bushing I Perfluoroelastomer (FFKM) secondary seals

N Carbon (versus reaction-bonded silicon carbide) 075 Installed on a nominal 75-millimeter shaft 53A Plan 53A

Standard Piping Plans and Auxiliary Hardware

Annex G of the 4th edition is generally reorganized and includes six new piping

plans:

Plan 03 gives purchasers the option of using the seal chambers special features toenhance circulation or venting in the machinery.

Plan 55 is an externally circulated buffer (unpressurized) fluid for Arrangement 2seals.

Plan 65 is now subdivided into 65A and 65B. End users can use Plan 65A to detectan excessive leakage flow rate and Plan 65B to detect a certain amount of

cumulative leakage.

Plans 66A and 66B are new to the standard, although end users have used thempreviously in pipeline applications. These plans detect and restrict excessiveleakage rates in case of an Arrangement 1 seal failure.

Accessories

The 4th edition now requires Plan 52, 53A, 53B and 53C systems to have a

sufficient working volume of buffer or barrier fluid for at least 28 days of

operation without refilling. As a point of reference, the default reservoir for Plans


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52 and 53A has a three-gallon capacity, or pot, for pump shafts smaller than 2.5

inches and a five-gallon pot for larger shaft sizes. Plan 53C must have the same

working volume of fluid as Plan 53A. For Plan 53B, the default bladder and

accumulator sizes are five gallons and nine gallons, respectively. The design of

Plan 53B systems can be complex, especially when ambient temperatures vary

widely, and purchasers should become familiar with the calculations and

procedures in the 4th editions Annex F tutorial. The new edition also discusses the

option of adding a pressure gauge and isolation valve to check the accumulator or

bladders integrity in a Plan 53B system.

The change from switches to transmitters with local indicators is the most obvious

and significant change to the systems instrumentation in the 4th edition. End users

requested this change, stating that it is consistent with evolving best practices.

Nonetheless, the change from simple switches to transmitters is likely to be

controversial and expensive. If purchasers want to continue to use switches, they

now have to request them in their specifications or data sheets.

Generally, the updated standards approach to accessories is more pragmatic than

in previous standards. For example, the standard notes that some instruments may

not be exposed to the pumps maximum allowable working temperature and that it

is acceptable for those instruments to have a lower design temperature. The

updated standard now also addresses natural draft air-cooled heat exchangers but

does not address forced draft systems.

Data Transfer and Data SheetsThe 4th edition has revised the data sheets in Annex C extensively to make them

the same for all seal categories. Only two data sheets are included in the 4th

editionone in metric units and one in U.S. customary units. The new edition also

folds Annex J into Annex E.

Inspection, Testing and Preparation for Shipment


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In an organizational change, Section 10 of the standardInspection, testing and

preparation for shipmentis now divided into two sections. In light of the

additional orientations and configurations included in this edition, the standard has

revised the qualification test procedures and moved them into Annex I. Section 10

still includes all other requirements.

Section 10 also features a clearer version of the assembly integrity test, or air test.

This simple, yet often misunderstood, test is based on two decades of practical

experience and is intended to show whether the cartridge is assembled correctly.

Previous editions of API 682 required metal plugs and anaerobic sealants when

shipping new or repaired cartridges. After much debate, the task force decided that

threaded connection points should be protected with plastic plugs for shipment.

These plastic plugs should be red and have center tabs that operators can pull

easily to distinguish the plugs from metal plugs. Shippers should also attach yellow

warning tags to the plugs to indicate that end users need to remove the plugs before

operation.

Technical Tutorials and Illustrative Calculations

Although tutorial notes are scattered throughout API 682, this edition expands the

tutorial section, Annex F, from seven pages to 42 pages. The expanded annex

includes illustrative calculations. In particular, users interested in systems such as

Plan 53B will find Annex F to be useful.

A Comprehensive Guide

The 4th edition of API 682 is the product of more than 20 years of discussion,debate, usage and peer review. It includes a strong set of defaults and is by far the

best and most logical starting point for mechanical seal and systems use.

Equipment operators should take the time to familiarize themselves with API 682

to get the most out of this comprehensive standard.

Documents

Prepare for the 4th Edition of API 682