As with every intended use for valves, piping carries its own set of standards that valve companies and users need to understand. This article provides an overview of the codes (it does not necessarily cover detailed requirements for specific services).
The typical piping codes used in the valve industry (excluding the water industry) are ASME B31.1 for Power Piping 2014, ASME B31.3 for Process Piping 2014, ASME B31.4 for Pipeline Transportation Systems for Liquids and Slurries 2012, and ASME B31.8 for Gas Transmission and Distribution Piping Systems 2014.
In each of these codes, valves are listed in tables. When that’s the case, no additional requirements are generally placed on the valve manufacturer and supplier besides the valve product standards (e.g., API 6D, ASME B16.34, etc.). Although special cases exist, such as class M in B31.3, they are not discussed in this general overview.
The question also arises about what happens in situations that call for non-listed valves. These situations vary from piping code to code so they should be examined on a case-by-case basis.
The ASME B31.1 code lists three valves standards, excluding cast iron and bronze valves. The standards are: 1) ASME B16.34, Valves–Flanged, Threaded, and Weld End; 2) MSS SP67–Butterfly Valves; and 3) MSS SP68–High Pressure Butterfly Valves with Offset Design. As stated in B31.1, para 107.1, “Valves not complying with above [the list] shall be of a design, or equal to the design, that the manufacturer recommends for the service as stipulated in para. 102.2.2. Such valves shall be pressure tested in accordance with MSS SP-61.”
This puts the responsibility on the valve manufacturer to recommend the design for the service and compounds the issue when valves are supplied through distribution. Rarely will the valve manufacturer know the actual service, since that manufacturer is not responsible for the piping system. Therefore, it is essential that the designer of the piping system clearly understands what is offered when the valve is unlisted. This is especially important with respect to pressure/ temperature ratings. The piping designer should always check the suitability of the valve for the service.
The ASME B31.3 code lists four valve standards, again excluding cast iron and bronze valves. The standards are: 1) ASME B16.34, Valves–Flanged, Threaded and Welding End; 2) MSS SP72–Ball Valves with Flanged or Butt-Welding Ends for General Service; 3) API 608–Metal Ball Valves with Flanged, Threaded and Welding Ends; and 4) API 6D–Specification for Pipeline and Piping Valves.
The API 6D standard was added in the 2014 edition of this code with a caveat that the design of valves comply with ASME B16.34. (Therefore, it does not really add anything to the 2012 edition list).
Valves that are not listed may be used only in accordance with paragraph 302.2.3. Unless pressure/temperature ratings are established by the method set forth in ASME B16.34, pressure design is qualified as required by paragraph 304.7.2.
In the 2014 edition of ASME B31.3, the designer has to be satisfied that composition, mechanical properties, method of manufacture and design are suitable for the intended service. The pressure/temperature ratings should be established in accordance with rules in paragraph 304. The change from the 2012 edition to the 2014 edition caused the onus to fall on designers. This is because the 2012 edition states that pressure design shall be verified in accordance with paragraph 304 of the code; however, the latest edition states the designer has to be satisfied the design is suitable for the intended service. The situation is similar to what happens with B31.1 since the manufacturer rarely knows the service.
ASME B31.4 lists eight valve standards, once again excluding cast iron and bronze valves.
These valve standards, which are more comprehensive than the previous codes, are:
- ASME B16.34, Valves–Flanged, Threaded, and Welding End
- MSS SP68–High Pressure Butterfly Valves with Offset Design
- MSS SP72–Ball Valves with Flanged or Butt-Welding Ends for General Service
- API 600–Steel Gate Valves-Flanged and Butt-Welding Ends, Bolted Bonnets, Twelfth Edition
- API 602–Steel Gate, Globe and Check Valves for Sizes DN 100 and Smaller for the Petroleum and Natural Gas Industries
- API 603–Corrosion-resistant, Bolted Bonnet Gate Valves-Flanged and Butt-Welding Ends
- API 6D–Specification for Pipeline and Piping Valves
- API 6A–Specification for Wellhead and Christmas Tree Equipment
In this code, special valves not on the list are permitted, provided the valve design is of at least equal strength and tightness, the valves are capable of withstanding the same test requirements as covered in the above standards, and the valve’s structural features satisfy the material specification and test procedures of the valves in similar service set forth in the standards. These requirements are stricter than previous codes, requiring the designer to make the valve with equal strength and tightness.
The ASME B31.8 code lists five valve standards, excluding cast iron and thermoplastic valves. These standards are: 1) ASME B16.33–Manually Operated Metallic Gas Valves for Use in Gas Piping Systems up to 175 psi (Sizes NPS1/2 Through NPS 2); 2) ASME B16.34 Valves–Flanged, Threaded and Welding End; 3) ASME B16.38–Large Metallic Valves for Gas Distribution: Manually Operated, NPS 21 .2 (DN 65) to NPS 12 (DN 300), 125 psig (8.6 bar) Maximum; 4) API 6D–Specification for Pipeline and Piping Valves; and 5) API 6A–Specification for Wellhead and Christmas Tree Equipment.
ASME B31.8 does not have criteria for unlisted valves. It states that “Valves shall conform to standards and specifications referenced in this Code and shall be used only in accordance with the service recommendations of the manufacturer.” This means that with the 31.8 code, one must only use valves that are listed.
The common standard for valves is ASME B16.34. While this standard has several aspects that are positive, it is not really a design code like ASME BPVC section VIII, where material strength, corrosion allowance and formula for irregular shapes are taken into account. For this reason, designs should be cross checked against a pressure vessel code.
While compliance with the piping codes is necessary in almost all cases, compliance with national and federal laws is obligatory. In the U.S., federal codes on oil and gas transportation add restrictions to the valve standards in the piping codes.
The U.S. federal code for Transportation of Natural and Other Gas by Pipeline in section 49 CFR 192.145 states:
“Except for cast iron and plastic valves, each valve must meet the minimum requirements of API 6D (incorporated by reference, see §192.7), or to a national or international standard that provides an equivalent performance level. A valve may not be used under operating conditions that exceed the applicable pressure-temperature ratings contained in those requirements.”
This federal code mandates the requirements of API 6D for minimum requirements for pipelines designed per ASME B31.8, which rules out a number of the valve standards listed. For others, it adds substantial additional features and testing over and above the requirements of those standards (e.g., ASME B16.34).
Meanwhile, the U.S. Federal Code for Transportation of Hazardous Liquids by Pipeline in section 49 CFR 195.116 states each valve installed in a pipeline system must comply with the following:
- The valve must be of a sound engineering design.
- Materials subject to the internal pressure of the pipeline system, including welded and flanged ends, must be compatible with the pipe or fittings to which the valve is attached.
- Each part of the valve that will be in contact with the carbon dioxide or hazardous liquid stream must be made of materials that are compatible with carbon dioxide or each hazardous liquid that it is anticipated will flow through the pipeline system.
- Each valve must be both hydrostatically shell tested and hydrostatically seat tested without leakage to at least the requirements set forth in section 11 of API Standard 6D (incorporated by reference, see §195.3).
While the federal code for transportation of hazardous liquids does not follow all of the guidelines of API 6D, it does follow that standard’s testing requirements for pipelines designed per ASME B31.4. The main differences from the other listed codes are that test durations are longer and that metal-seated valves are allowed a larger leakage rate because the code was created mainly for larger valves.
Other regulatory bodies, such as the U.S. Coast Guard and the Occupational Safety and Health Administration, do not prescribe additional requirements on top of the piping codes.
In summary, for the product transportation codes ASME B31.4 and B31.8, when the valves are intended for use in the U.S., the sensible valve manufacturer would ensure that design, manufacture and testing encompass ASME B16.34 and API 6D. In the case of ASME B31.1 and B31.3 codes, if the valve is not listed on the table, the piping system designer has to check the suitability of the valve for service or has to clearly advise the manufacturer of intended service conditions.