API 6D

Valve Standards in The Petrochemical & Refining Industry
by Greg Johnson, President, United Valve
Originally published in the summer 1996 issue of Valve Magazine

Valves in petrochemical and refining installations are subject to numerous standards and specifications issued by many supporting organizations. Today's valve standards are dynamic documents that reflect sound engineering practice, changes in market demands and changes in technology and manufacturing procedures.

This document focuses on some of the important standards that affect steel, gate, globe and check valves in refineries and petrochemical installations. Some mention will also be made of other valve specifications, however specifications for control and relief valves will not be covered.

Early in this century, when our nation's petrochemical and refining industries were in their infancy, pipe, valve and fitting (PVF) manufacturers as well as end-users had no standards to go by. The design and function of their products were dictated and affected by actual feedback from the end user - be it years of effective service life, catastrophic failure or incompatibility with similar products from other manufacturers. This lack of valve, flange & fitting interchangeability with other manufacturers products, resulted in two primary groups addressing the standardization issue.

One group, The Manufacturers Standardization Society of the Valve & Fitting Industry (MSS), issued its first standard in 1924, and is still today at the forefront of valve standards activities. Over the years many MSS documents have been the basis for follow-up ASME and American Petroleum Institute (API) standards. The American Standards Association (ASA) published their first document covering standardized flanges and flanged fittings in 1927.

As the steam powered industrial revolution churned across the United States during the first quarter of this century, concern over boiler and pressure vessel design increased as some catastrophic disasters involving pressure vessels resulted in great loss of life and property. This situation led to the creation of the "Boiler Code", which forever altered the future of all pressure containing components, including valves.

The “Boiler Code”, officially known as the American Society of Mechanical Engineers (ASME) Boiler & Pressure Vessel Code (B&PVC), laid the groundwork for many specifications and standards which have affected the PVF industry. The first edition of the Code was published in 1915. It is still published and updated yearly by ASME. Over the years the Code has come to assure manufacturers, designers and the public, of the safety and reliability of pressure equipment.

The fever pitch pace of oil & chemical production during world war II, dictated the creation of additional valve standards. The years immediately following the war saw the creation of many of the first edition of standards that are now in everyday use. The advent of pressure seal bonnet technology also required a new basis for determining pressure ratings of valves that led to standards such as MSS SP-66, "Pressure Ratings For Steel Buttwelding End Valves".
The nuclear power industry of the 50's & 60's forced the creation of even more standards and specifications affecting the valve manufacturers and end-users. Today, increased concern for the environment, plant worker safety and the general public, has created valve standards that are technologically extensive and in many cases also legally driven.

All aspects of valve design, functionality, inspection and testing are covered in dozens of ASME, API and MSS documents. This dizzying amount of codes, standards and specifications can make the specification and procurement of valve products a job for only a seasoned valve engineering expert. Unfortunately, gold plated watches and summer retirement homes have taken their toll, by drastically reducing the number of experienced valve trained personnel familiar with valve specifications and standards.
This situation puts more responsibility on both the manufacturer and valve purchaser/specifier. A good understanding of the primary standards affecting these products is paramount. I recommend that anyone involved in specifying or purchasing valves have current copies of all the valve standards that apply to the products being purchased.

Here are capsule summaries of some of the more common valve specifications used in the petrochemical & refining industry today.

API 600 Steel Valves - Flanged & Buttwelding Ends
API 600 is the primary steel gate valve purchase specification. Valve design and construction criteria are detailed, as well as materials and trim designations. An appendix contains information pertaining to pressure seal valves. ISO Standard 10434 is essentially the same as API 600, only published in the ISO format.

API 602 Compact Steel Gate Valves- Flanged, Threaded, Welding and Extended-Body Ends
API 602 is the 4" & smaller forged steel gate valve purchase specification. Valve design and construction criteria are detailed, as well as materials and trim designations. Future versions of this document are expected to include requirements for bellows seal gate valves.

API 603 Class 150, Cast, Corrosion-Resistant, Flanged-End Gate Valves
API 603 covers light walled gate valves in sizes NPS 1/2" through 24", in classes 150, 300 & 600. These valves are used in applications where the thicker API 600 casting is not needed.

API 608 Metal Ball Valves-Flanged and Butt-Welding Ends
API 608 is the purchase specification for class 150 and class 300 metal ball valves. Valve design and construction criteria are detailed. Important Note- ball valve working pressures should be based on seat material, not valve class.

API 609 Butterfly Valves, Lug-Type and Wafer Type
API 609 is the purchase specification for butterfly valves with lug-type and wafer-type configurations designed for installation between ANSI B16 flanges, through Class 600.

API 598 Valve Inspection & Testing
API 598 covers the testing and inspection requirements for gate, globe, check, ball, plug & butterfly valves. Steel valve pressure ratings found in ASME/ANSI B16.34 are required to determine API 598 test pressures for steel valves.

API 6D Specification for Pipeline Valves (Gate, Plug, Ball and Check Valves)
Specification for Pipeline Valves (Gate, Plug, Ball and Check Valves)
API 6D is the primary standard for valves used in pipeline service, including gate, plug, ball and check valves. Occasionally refinery and petrochemical purchasers will reference the more stringent testing requirements of 6D although the valve may have built under API 600, 602, 608 or 609 design criteria.

ASME/ANSI B16.34 Steel Valves - Flanged & Buttwelding Ends
ASME B16.34 is the base document from which steel valve pressure/temperature ratings are derived. It also offers additional valve specification data including nondestructive examination procedures for upgrading valves to Special Class. Note: Gate valves manufactured under B16.34 wall thickness minimums may not meet the minimum wall thickness requirement of API 600 & API 602 for class 150, 300 and 600.

ASME/ANSI B16.10 Face-to-Face Dimensions of Ferrous Valves
B16.10 lists the face to face dimensions of all flanged and buttweld end valves. Screwed and socketweld end valve face-to-face dimensions are not included in this specification.

MSS SP-55 Quality Standard for Steel Castings for Valves, Flanges and Fittings and Other Piping Components
SP-55 details the visual inspection criteria for castings. This specification is listed as part of the procedure under API 598. NACE MR-0175 Standard Material Requirements for Sulfide Stress Cracking Resistant Metallic Materials For Oilfield Equipment MR-0175 is the "standard" for materials used in "sour" environments such as found in piping systems in many refineries. It lists materials, mechanical properties and heat treatments for metals used in Hydrogen Sulfide bearing hydrocarbon service.


Gate Valves

For users of gate valves, API 600 is the key document. It details all design and material criteria. API 600 also lists important dimensions such as stem diameter minimums, wall thickness and stuffing box size.

Small carbon steel gate valves such as the forged 150#, 300#, 600#, 800# & 1500# class valves manufactured by several companies worldwide are covered by API 602. This specification covers the same details small forged gate valves that API 600 does for larger valves. API 602 further gives dimensions for extended body valves which are used extensively in industrial facilities.

Another important gate valve specification is ASME B16.34. This document gives extensive details on valves built to ASME boiler code pressure temperature ratings. One important area in which API 600 differs from ANSI B16.34 is minimum wall thickness. API 600 requires a heavier wall for a given pressure rating than does ASME B16.34. API 602 also requires a heavier wall for 150#, 300# & 600# classes than does B16.34.

Testing

Valve testing specifications have come a long way since the early days of the steel valve business. Looking through valve manufacturers' catalogs of the 40's and 50's you see a multitude of pressure ratings and test pressures listed. Part of the problem was indeed lack of standardization. Many products were rated with working pressures (i.e.. 800 psi WOG - which meant 800 psi working pressure for water, oil or gas service), instead of the pressure classes we are accustomed to today. Standardized ASME/ANSI pressure classes have alleviated this confusion as to pressure/temperature ratings and test pressures for most steel valves.

The defacto test specification today is API 598 "Valve Inspection & Test". First drafted in 1974, this document lists all of the test parameters and procedures to be followed for production testing of valves. Most metallic seated valves larger than ANSI 2" size have an allowable leakage rate; this is listed in API 598 as well. Some valve types such as bronze gate, globe & check valves are usually not tested per API 598. These are normally tested per MSS SP-61 "Pressure Testing of Steel Valves".

Occasionally the chemical or refinery valve specifier will see reference to API 6D - "Pipeline Valves". This document is a thorough standard covering the design, materials and dimensions of valves for pipeline service. The most common reference for non-pipeline use are the testing requirements which differ slightly from API 598. The primary difference being 6D's zero allowable leakage on closure tests. Since most of the valves built to API 6D are resilient seated, this is no problem, however when the test standard is applied to metallic seated wedge gate, globe or check valves, compliance can be difficult.

What about globe & check valve standards? Conspicuous in their absence are the steel globe and check valve standards. There is always some talk at valve industry gatherings about globe valve specifications, but so far there has been no action. Due to the inroads that quarter turn valves have made in a field once dominated by globe valves, there probably won't be any specification in the near future. Most designers and specifiers will use ANSI B16.34 as far as applicable for their globe and check valve specifications. Great Britain's British Standards Institute does have two standards that address globe valves: BS 1873 "Steel Globe Stop and Check Valves For The Petroleum, Petrochemical and Allied Industries" and BS 5352 "Steel Wedge Gate, Globe and Check Valves 50mm (2") and Smaller For The Petroleum, Petrochemical an Allied Industries.
NACE MR0175

While not a standard, but a recommended practice, the National Association of Corrosion Engineers (NACE) specification MR-01-75, "Standard Material Requirements for Sulfide Stress Cracking Resistant Metallic Materials For Oilfield Equipment" is almost treated as a standard in many industries. MR-0175 was first published to help solve problems with material failures caused by the presence of hydrogen sulfide (H2S) in oil well equipment and gathering facilities. Although created as an "upstream" equipment document, MR0175 has been adopted by numerous industries and agencies. MR0175 lists materials (by UNS number) and fabrication techniques.

Designed to lessen the likelihood of H2S induced cracking, "NACE" trim as it is often called, is specified quite often for use in refinery processes. The most common "NACE" trim materials used in valve construction today are 316ss, Monel and Stellite.

ASME Codes

Although not valve standards as such, there are three important ASME documents that are important to fabricators welding valves into piping components and manufacturers utilizing welding in the manufacturing process.

First is ASME B&PVC, Section IX "Welding & Brazing Qualifications". This document addresses welding procedures, welding procedure qualifications and welder certifications. Most, if not all, pressure vessel welding codes specify Section IX as part of their process.
The other two are "construction" codes. ANSI/ASME B31.3 "Chemical Plant And Petroleum Refinery Piping", details the fabrication, assembly and nondestructive testing of piping systems, which include valves. Many valve manufacturers utilize B31.3 for their in-house fabrication procedures. The other construction code is Section VIII, "Rules For The Construction of Pressure Vessels - Division 1", of the B&PVC. Code. Section VIII also details fabrication, assembly and nondestructive testing requirements. There are additional construction codes used for pipeline, power and refrigerated piping industries.

Several non-domestic standards organizations publish valve standards, including the British Standards Institute (BSI), International Standards Organization (ISO) and The Canadian Standards Organization (CSA). BSI publishes several standards covering areas that U.S. valve standards writers have ignored such as: globe valves - BS 1873 & BS 5352, cryogenic valves - BS 6364 and steel check valves - BS 1868 & BS 5352. These documents are excellent starting points for persons needing guidance in these particular areas.

The Future For U.S. Valve Standards

What does the future hold for United States valve standards? As more and more valve production moves to foreign soil, unfortunately so does some of the power to direct and control valve standards. During the past several years there has been cooperation between the International Standards Organization (ISO) and US valve standards makers, however some domestic standards making bodies have justifiably been reluctant to give up total control of documents they have invested much time, effort and expense in creating, for a return of relatively nothing.

The biggest dark cloud over the horizon for domestic standards organizations is the debate over metrification. If future valve and fitting standards take on more of an ISO flavor, the costs could be considerable. Metrification can be either "soft" or "hard" in terms of change from our imperial measuring units. Soft metrification merely changes the current unit of measurement to metric while maintaining the actual measurements. Hard metrification on the other hand, will not only change units of measure, but actually change dimensions. Obviously hard metrification is a major economic factor to be faced by valve manufacturers and end-users currently using or manufacturing valves and fittings.

All of the specifications listed in this article can be ordered from the sponsoring agencies, but there are other sources as well. Information Handling Services (IHS) in Englewood, Colorado offers many standards packages on CD ROM. There are many advantages to having the specification on computer, such as the ability to look up subjects by key word. However the biggest advantage has to be the automatic yearly update service, which insures you always have the latest copy of each cataloged specification. This update service helps meet the "most current document" requirements of ISO 9000 quality programs.

Two technical bookshops that carry extensive inventories of standards and specifications are Brown Book Shop in Houston, TX and Global Engineering Documents in Englewood, CO. Global also has a large inventory of obsolete and out-of-date specifications.
Over seventy-five years of valve standards have helped the refining and petrochemical industries grow and prosper throughout the world, with assured interchangeability of products by different manufacturers, as well as timely design changes. The committees that formulate these standards are hard working volunteers who care a great deal for their industries and the people affected by them. Standards committee meetings sometimes take on the air of a hearty democrat vs. republican congressional debate, but as the manufacturers state their case and the end-users theirs; the end result usually ends in acceptable compromise.

As long as these concerned, motivated industry representatives are writing the standards we must all work with, the industry can feel secure that present and future valve specifications will reflect the changing needs of the industry and the general public.



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