THE INCREASE IN GLOBALLY SOURCED PRODUCTS AND MUCH-REDUCED DOMESTIC MANUFACTURING HAS CAUSED EVERYONE IN THE VALVE SUPPLY CHAIN TO REQUEST AND REQUIRE MORE TESTING. HERE’S A LOOK AT SOME OF THE MOST COMMON VALVE TESTING STANDARDS IN USE TODAY.
“Testing, testing, 1 2 3…” We’ve all heard those words before as some nervous master-of-ceremonies tries to test the performance of the sound system over the tinkle of glass and the low roar of the after-dinner crowd. Wouldn’t life in the valve world be a whole lot easier if we could just utter a few words and become instantly convinced as to the quality and performance of our valves?
Today, more than ever before, testing is extremely important in the valve industry. The increase in globally sourced products and much-reduced domestic manufacturing has caused everyone in the valve supply chain to request and require more testing.
In order to effectively test a valve, there first must be an established testing procedure, combined with the acceptance criteria or performance standards that the valve is expected to meet or exceed. When it comes to testing standards though, one size does not fit all. There are different standards for bronze valves, steel gate valves, iron valves, pipeline valves, control valves and pressure-relief valves.
Up until about 1968, the acceptance criteria for most valve types were pretty simple: They weren’t expected to leak during testing. The most common valve design standard for the past 50 years has been the American Petroleum Institute (API) valve standard for refinery use, known today as API 600, “Bolted Bonnet Steel Gate Valves for Petroleum & Natural Gas Industries.” For 20 years, the document also contained valve testing criteria, and that criteria was pretty tough: “Valves shall show no leakage when subjected to a hydrostatic (or air) seat test.”
Today, most valve manufacturers strive for and achieve a zero closure test leakage rate during initial factory testing of their metal seated gate and globe valves. However, the predominant valve testing standard, API 598, “Valve Inspection and Test,” does have allowable leakage rates for these types of valves in sizes above NPS 2. Virtually all test specifications for resilient-seated valves require they exhibit zero leakage during the test period.
Determining Test Pressures
The first order of business in valve testing is determining the pressures at which the tests are to be performed. Many standards, such as API 598, do not list detailed pressures, only the procedure for testing. The actual test pressures are derived from pressure ratings that have been developed based on the materials of construction and design criteria, such as wall thickness.
In the early days of valve manufacturing, only two common valve materials were available, cast iron and bronze, and three pressure ratings: standard, medium and extra heavy. There was also no common definition of any of these ratings. Catalogs often described the factory tests and in some cases included the actual bursting pressure, so users could assign whatever working pressure and safety factor they wished.
Around 1930, the American Standards Association (ASA), in its B16e document, “Flanged and Welding-End Steel Wedge Gate and Plug Valves for Refinery Use,” created a common set of pressure ratings for the various valve classes we know today—class 150, class 600, etc… Except for class 150, all of the ratings were based on the class number’s pressure rating at 750o F steam. Class 150 for some reason was based on steam at only 500o F steam.
Figure 1—Original ASA pressure temperature ratings
|Class||Rating pressure & temperature|
|150||150 psi @ 500o F|
|300||300 psi @ 750o F|
|600||600 psi @ 750o F|
|900||900 psi @ 750o F|
|1500||1500 psi @ 750o F|
The successor to B16e was the currently in-use standard by the American Society of Mechanical Engineers, ASME B16.34, “Valves-Flanged, Threaded, and Welding End.” B16.34 is the mother document from which many testing specifications establish their baseline test pressures. The ASME document specifies the working pressure for the established pressure classes in a vast range of materials from low-carbon steel to exotic alloys. From this working pressure—for example, 285 psi for WCB, class 150 valves—the test pressures are derived.
If we were using API 598 as our testing standard, the 285 psi class 150 working pressure would become 325 psi for the backseat and high-pressure closure test (285 x 1.1) and 450 psi for the shell test (285 x 1.5). The actual results are rounded up to the next 25 psi point. ASME B16.34 does contain a testing procedure; however, its closure test protocol contains no acceptance criteria as that data is deemed “out of the scope of the document.”
The U.S. valve industry’s shift to a more global posture, combined with the huge increase in foreign valve manufacturers, has put increasing focus on international valve standards. The primary International Organization of Standardization (ISO) valve standard is ISO 5208, “Industrial Valves – Pressure Testing of Valves.” The standard is similar to the API 598 document, but recent updates have separated it more and more from the U.S.-developed standard. One of the key differences between ISO 5208 and API 598 is that the ISO document has a choice of four leakage rates, from gross leakage to zero. The ISO document also widens the users vocabulary by one word—“obturator.” An obturator is the closure element of a valve and in the ISO document it replaces the term disc or wedge.
Another difference in many ISO valve standards is that they also include testing criteria within their base design document. This has not been the case for the past 40 years for most steel and alloy valves in the United States. However, there is more and more talk at standards development meetings about adding test criteria to design specifications, such as many of the API valve standards.
While steel valve specifications such as API 600 have yet to be augmented with testing criteria, there are several U.S. valve standards that do have self-contained testing procedures. These are primarily iron and bronze valve standards and are covered by a host of Manufacturers Standardization Society (MSS) documents.
Special Valves, Special Tests
Control and pressure relief valves (PRV) are special purpose valve types and it follows suit their test procedures are unique as well. The primary goal of PRV testing is to confirm that the valve will both lift (open) at the correct pressure and provide the prescribed rate of flow. A control valve is normally tested to measure its rate of flow as well. Both PRVs and control valves are also tested to confirm the integrity of their pressure envelope.
PRVs are tested in accordance with two primary standards: ASME PTC 25, “Pressure Relief Devices” and API 527, “Seat Tightness of Pressure Relief Valves.” The common testing standards for control valves are ISA—the Instrumentation, Systems and Automation Society of America ISA-S75.19 and Fluid Controls Institute (FCI) FCI 70-2, “Control Valve Seat Leakage.”
The upstream pipeline and petroleum valve industry also have their own testing specification. It is located within the pages of the API 6D, “Pipeline Valves” valve design document. API 6D leakage rates are very close to those of API 598, but its holding times are longer.
Increasingly stringent clean air regulations have created the need for a new type of valve test, the fugitive emissions (FE) test. In FE testing, the goal is to determine the degree of minute leakage, if any, from the packing and gasket areas. The test requires pressurization of the pressure envelope with either methane or helium. Then the sealed valve is inspected with a sniffer device that measures any leakage in parts per million. The goal of most FE testing is to confirm that leakage rates are lower than 100 ppm or in some cases 50 ppm. The most common FE testing standards are ISO 15848, “Industrial Valves, Fugitive Emissions – Measurement, Test and Qualification Procedures” and API RP622, “Type Testing of Process Valve Packing for Fugitive Emissions,” although specific end-user standards are also very prevalent.
Nearly all valve test standards are designed to test valves at ambient temperatures, generally from 60° F to 120° F. But what about valves designed for low-temperature operation, such as liquid natural gas (LNG) or gas separation service? These cryogenic valves have their own testing standards, the most widely used being the British Standard Institution’s BS6364, “Valves for Cryogenic Service.” MSS has also developed a cryogenic standard that contains test criteria, SP-134, “Valves for Cryogenic Service, including Requirements for Body/Bonnet Extensions.” A third cryogenic testing standard is currently under development by an ISO work group.
Figure 2—Common valve types and their related test standards
|Valve type||Common test standard|
|Steel gates, globes and checks||API 598|
|Cast Iron gates||API 598, MSS SP-70*|
|Bronze gates, globes and checks||MSS SP-80*|
|Pressure seal valves||ASME B16.34*|
|Steel valves larger than NPS 24”||ASME B16.34*|
|Pipeline valves||API 6D*|
|Cast iron globes||API 598, MSS SP-85*|
|Cast iron checks||API 598, MSS SP-71*|
|Cast iron plugs||API 598, MSS SP-78*|
|Steel ball valves||API 598|
|Steel butterfly valves||API 598|
|Cryogenic valves||BS 6364, API 598|
|Pressure relief valves||ASME PTC 25, API 527|
|Control valves||ISA-S75, FCI 70-2|
*Test requirements contained within design standard
Key Valve Testing Standards
Here is a summary of some of the most common valve testing standards:
API 598, “Valve Inspection and Test” – The most widely used test specification in the world today. The document covers all types of valves in sizes through NPS 24. It also includes leakage rates and testing criteria for metal-seated and resilient-seated valves.
API 527, “Seat Tightness of Pressure Relief Valves” – This document covers the seat tightness of pressure relief valves. It also includes allowable leakage rates for testing with steam, water and air.
ASME B16.34, “Valves – Flanged, Threaded and Welding End” – The primary valve design document, it also contains charts for determining the working pressures of valves to be used in conjunction with other test standards, such as API 598. B16.34 contains a test procedure, but no seat leakage acceptance criteria.
ASME PTC 25, “Pressure Relief Devices” – The main reference document for the testing of pressure relief valves, PTC 25 contains detailed procedures for testing relief valves with air or steam.
FCI 70-2, “Control Valve Seat Leakage” – This document contains detailed test procedures and leakage rate classes for control valves. The leakage classes are also occasionally referenced by other documents and used as acceptance criteria.
ISA-S75, “Hydrostatic Testing of Control Valves” – It provides a procedure for the hydrostatic shell testing of control valves. Closure testing and acceptance criteria are out of the scope of this document and usually are covered by referencing FCI 70-2.
ISO 5208, “Industrial Valves, Pressure Testing of Valves” – ISO’s primary testing standard, this document covers all types of valves and has four levels of allowable closure test leakage.
MSS SP61, “Hydrostatic Testing of Steel Valves” – Similar to API 598, this document has some subtle differences in test holding times and leakage rates.
MSS SP70, “Cast Iron Gate Valves, Flanged and Threaded Ends”– The primary design document for cast iron gate valves, it also contains testing procedures and acceptance criteria.
MSS SP71, “Cast Iron Swing Check Valves, Flanged and Threaded Ends” – The primary design document for cast iron check valves also contains testing procedures and acceptance criteria.
MSS SP78, “Cast Iron Plug Valves, Flanged and Threaded End” – The primary design document for cast iron plug valves also contains testing procedures and acceptance criteria.
MSS SP80, “Bronze Gate, Globe, Angle and Check Valves” – The primary design document for commodity bronze valves also contains testing procedures and acceptance criteria.
MSS SP85, “Cast Iron Globe & Angle Valves” – The primary design document for cast iron globe valves also contains testing procedures and acceptance criteria.
What Lies Ahead?
What does the future hold for valve testing standards? As mentioned earlier, there is a trend in some standards-creating bodies to include the testing specifications within the primary design document, and we may see more of that practice sooner rather than later. The fugitive emissions issue could also foster the creation of a user friendly, production-type FE valve test method. The current FE testing protocols are primary design or prototype verification procedures and not easily adapted to production testing usage.
Valve testing techniques have changed over the years and at the same time test procedures have become more thorough. But one thing is for certain: As long as men and women, or automated robots for that matter, are building valves, there will always be a need for valve testing and effective testing standards to govern those tests.
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