The realization of safe and smooth operations of industrial processes is heavily reliant on valves performing their function with precision. Thus, valve testing ensures that these valves meet design specifications for the duration of their operational life.
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Generally, valve testing simulates operating conditions in a controlled environment to ensure fit for service valves. However, testing also occurs periodically after installation in line with standard practices.
In this article, we will review common valve testing types and industry standards that offer guidelines for valve testing.
There are several types of testing to which a valve could undergo. The required test depends on the application, manufacturer standards, and customer specifications. The following sections examine common tests, an overview of their procedure, and industry guidelines.
General Pressure Testing
This test involves filling a valve body with a testing fluid, which is usually water with a corrosion inhibitor. Then, technicians apply pressure over a specific period of time. The time and level of pressure varies depending on factors including the valve material, valve size, and category of pressure test. But in most cases, the pressure level is higher than the operational/working pressure of the valve. Also, the procedure for the pressure test varies depending on the type of valve in question. Generally, pressure tests aim to ascertain the integrity of the valve shell, seat, and seal against leakages due to pressure. After carrying out a test, a valve will not be accepted if the following occurs:
- There is any distortion that disrupts the valve operation, due to the test.
- Visible leaks anywhere in the valve body/bonnet assembly.
- Leakage via static seals (packing) and gasketed joints, except where permitted by design the test standard.
Common industry guidelines for pressure testing valves can be found in ASME B16.34, API 598, MSS-SP-61, API 527, and ISO . Many tests are recorded on paper wheel charts or manually, although digital options are becoming more prevalent.
Valve Test Read-out Stand, Courtesy: Axcel TS
Hydrostatic vs Pneumatic Pressure Testing
Although water (hydrostatic) is the most common test medium in pressure testing, some conditions require pneumatic pressure testing of valves. For pneumatic testing, air or an inert gas such as nitrogen are the preferred media. Generally, in industry, hydrostatic testing is ideal for high-pressure applications where the equipment is not moisture sensitive.
In situations where moisture can damage certain equipment &#; usually via corrosion &#; or alter the chemical balance in the system, pneumatic testing is recommended. Also, industry guidelines recommend the use of pneumatic testing for cryogenic and low temperature valves. This is because it is difficult to remove all water after the test. The presence of moisture in an operating system is highly discouraged. The table below highlights more of the differences between hydrostatic and pneumatic testing in line with standards and industry practices.
Hydrostatic Testing
Pneumatic Testing
Typically, the system is pressurized to at least 1.5 times above the maximum operating pressure for shell testing, and 1.10 times for seat testing.
Because it is used mostly for low-pressure applications, the system is usually pressurized to 10% above the maximum operating value or 100 psi max.
The use of pressure-relieving devices is recommended.
The use of pressure-relieving devices is mandatory.
Requires extensive post-test clean-up to avoid damage to components or disruption to the system when operation begins.
There is little or no need for cleaning after testing.
Usually records low rates of equipment failure.
It sees common equipment failure.
The process is straight-forward and poses less danger. Thus, semi-skilled personnel can oversee it.
Because of the dangers involved, an experienced operator supervises this process. For example, nitrogen leakage can gradually displace the air in the test lab and affect personnel. Also, the effects of overpressure are more catastrophic.
Hydraulic Testing vs. Pneumatic Testing
Note: Testing above 100 psi gas pressure can be very dangerous due to the expansion properties of a gas.
When pressure testing a valve, there are key components that are given a closer look for the duration of the process. Three of these include the shell, seal, and seat.
Shell Testing
The valve shell refers to the main body of the device. Moreover, its testing in the industry is driven mostly by guidelines from API 598 and ASME B16.34. Typically, the valve is mounted on a test bench and partially opened. Then, the shell is pressurized, with ASME B16.34 recommending a minimum of 1.5 times the valve pressure rating at 100 &#; (38 &#;) for hydrostatic testing. While that of pneumatic seat testing is 1.1 times the maximum allowable pressure. Pneumatic testing is done to 80-100 psi. Also, both the API and ASME standards recommend varying test duration depending on the size of the valve being tested. The table below summarizes the test duration.
Valve Size (Inches)
Test Duration (Seconds)
&#; 2.0
15
2.5 &#; 6.0
60
8.0 &#; 12.0
120
14.0 &#;
300
Valve Size vs. Test Duration For Shell Test
In addition, the test water temperature should range between 41 &#; (5 &#;) and 122 &#; (50 &#;). And the pressure gauge used for measurements should have calibration ranging from not less than 1.5 times the test pressure, to not more than 4 times the test pressure. For a valve shell to pass the test, there shall be no visible leakage for the duration of the test.
A valve stem seal (packing) is also monitored during the shell test. For adjustable stem seals, the occurrence of leakage during the test is NOT a cause for rejection, as long as the manufacturer can demonstrate the seal&#;s capacity to retain at least the maximum allowable pressure of the valve without any visible leakage. Adjustments to the packing are allowed to eliminate leakage. For non-adjustable stem seals, no leakage is permitted during the shell test.
Seat Testing
Typically, the valve seat test is carried out after testing the valve shell. With the same API and ASME standards as with the shell test providing guidance. The recommended pressure is 110% of the maximum allowable pressure at 100 &#; (38 &#;), and the test time varies with size in accordance with ASME B16.34.
Valve Size (Inches)
Test Duration (Seconds)
&#; 2.0
15
2.5 &#; 8.0
30
10.0 &#; 18.0
60
20.0 &#;
120
Valve Size vs. Test Duration For Seat Test
The test duration recommendations from API 598 are similar to these, and it also states the allowable leakage rates from the seat.
Valve Size (Inches)
Hydrostatic Leakage Rate (Drops Per Minute)
Pneumatic Leakage Rate (Bubbles Per Minute)
&#; 2.0
0
0
2.5 &#; 6.0
12
24
8.0 &#; 12.0
20
40
For valve sizes greater than 14 inches, the hydrostatic test leakage rate should not exceed two drops per minute per inch. While the pneumatic test leakage rate should be less than four bubbles per minute per inch.
Fire Testing
One of the requirements of industrial valves is having reliable fire protection. This holds particularly true for sensitive applications such as oil and gas, refinery, and petrochemical industries. Moreover, valves in these industries must guarantee a reliable and safe shut-off in case of a fire incident.
In a fire test, a valve is pressurized and subject to high-temperature flames between &#; (750 &#;) and &#; ( &#;) for a period of thirty minutes. During this period, the heat intensity and the leakages &#; both internal and external &#; are monitored and measured. Also, after extinguishing the flames and allowing the valve to cool, the technician test its pressure-retaining capacity. All through the test, the leakage levels should be within acceptable limits for the valve to pass as being &#;fire-safe&#;. Some key things to note about fire testing include:
- Leakages from the piping to valve end connections are not part of the acceptance criteria.
- Technicians measure temperature measurement from at least two places. One is 1&#; (25 mm) from the upper stem packing box on the horizontal centerline, while the other measurement point is 1&#; below the valve.
Standards such as API 607, API 6FA, ISO , BS , and BS constitute industry guidelines for fire testing. On the basis of these guidelines, several companies set up their bespoke procedure for fire-safety valves. Of all the fire testing guidelines, API 607 and API 6FA are the most widely used. API 607 provides testing criteria for valves with non-metallic seating and quarter-turn valves. API 6FA provides the testing criteria for metal seated valves.
Note: Most metal-to-metal seated Gates, Globes, and Swing checks are NOT tested to API 607 due to their inherently Fire Safe Design. (There are no soft parts to melt during a fire.)
Fugitive Emissions Testing
A fugitive emissions test aims to assess the impact of gas or vapor leakage from a valve. Although this leakage can be from anywhere along the piping system, statistics show that approximately 60% of fugitive emissions stem from valves. This data highlights the importance of this test. In addition, the impact of these emissions has significant consequences including:
- Increase in the risk of fire and explosion.
- Economic losses due to leakage of the commodity.
- Long-term health risk to the workers and communities in close proximity.
- Environmental damage.
When carrying out fugitive emission tests, the most common test gases are helium and methane. The valve is pressurized with the test gas at varying temperatures. Then technicians monitor for leakages via the sniffing or vacuum method. International standards such as API 622, API 624, API 644, ISO -1, and ISO -2 all provide guidance on how to carry out this valve test. However, most organizations develop their specifications to ensure application suitability.
Cryogenic Testing
Cryogenic testing of valves is done for those operating at low temperatures or in cryogenic service. The test procedure involves placing the valve within an insulated tank, with liquid nitrogen at temperatures of down to -320 &#; (-196 &#;).
Then, helium pressurizes the valve to the operating pressure specified for its class. During the test, technicians closely monitor the temperature inside the valve and leakages. In the end, the valve is depressurized and warmed up until it attains ambient temperature. Thereafter, a detailed report summarizes the performance of the valve and whether leakages were within acceptable limits. There are several international standards that provide guidelines for cryogenic valve testing including ISO -1, ISO -2, EN , and BS .
In addition to the standards mentioned in the previous section, there are a host of standards that provide recommendations for different valve types and test procedures. The table below provides a list of these standards and the areas of testing they cover, for quick referencing.
Applicable Standard
Valve Type and Test Procedure
API 598
Valve inspection and test. Testing of cast iron gate, plug, check, and globe valves. Also, testing of steel gate, globe, check, ball, and butterfly valves. Cryogenic valves.
API 527 and ASME PTC 25
Pressure relief valves.
API 6D
Testing of pipeline valves.
ASME B16.34
Pressure seal valves and steal valves larger than NPS 24 inches. Flanged, threaded, and welded end of valves.
MSS SP-80
Bronze gate, globe, angle, and check valves.
MSS SP-70, MSS SP-71, MSS SP-78 and MSS SP-85
Testing of cast iron valves, flanged, and threaded ends.
ISA S-75, ISO , and MSS SP61
Hydrostatic testing of valves.
FCI 70-2, ISA S-75
Control valve testing.
Standards for Valve Testing
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Valve passing at site
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Valve passing at site
Valve passing at site
onrush(Aeronautics)
(OP)
12 May 08 22:31
Dear members,
Based on API 589 closure test requirements, some passing (leakage) is permitted during manufacturer shop closure test.
However what about the passing at construction site during line hydrotest?
Is there any international code or standard for that case?
You know that the test pressure during line hydrotest at site may be lower than that during shop closure test.
Thanks in advance..
Replies continue below
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RE: Valve passing at site
NGiLuzzu(Mechanical)
16 May 08 11:11
I'm not aware of any International Standards dealing with line hydrotests of newly constructed plants (and I would be curious to read one...), but I believe every Engineering and End-User Company has own its own Specification.
You will not find an answer to your specific question, but you can probably read some stimulating hints about the same subject within
Regards,
'NGL onrush,I'm not aware of any International Standards dealing with line hydrotests of newly constructed plants (and I would be curious to read one...), but I believe every Engineering and End-User Company has own its own Specification.You will not find an answer to your specific question, but you can probably read some stimulating hints about the same subject within thread408-: "Zero Leakage" conept and EN std... Regards,
RE: Valve passing at site
BillBirch(Mechanical)
19 May 08 03:48
You should not be hydrotesting against valves during line hydrotesting. This is for verifying welds and other joints, so valve performance is not addressed. Xalves are normally removed or partially opened. In general, valves are only required to pass a test in the works. Years ago, an experienced (ball) valve designer and manufacturer told me he worked in the best business in the world - his product only has to work once (during the works test) and thereafter should always be assumed to pass.
RE: Valve passing at site
onrush(Aeronautics)
(OP)
19 May 08 06:18
Thanks, BillBirch
These valves are block valves to be installed in inlet of spare-pumps. It means that these valves are normally closed. What about this case? In this case, should the blank be used instead of valve?
RE: Valve passing at site
BillBirch(Mechanical)
19 May 08 09:02
Yes, blinds should be used because the test pressure is way above the capability that valve seats are expected to achieve.
RE: Valve passing at site
benensky(Mechanical)
11 Jun 08 17:40
BillBirch is right. I am a valve designer and we test and design our valve to seat at 110% of rated pressure (MSS SP 61 section 4). The valve shell is designed to meet or exceed 150% (Same standard section 3) ANSI B16.5 also requires the "flange fittings" to pass a 150% rating test (section 8.3), but that will only be against the shell also.
Many system hydro tests are done at 150% rated and will lift (open) the seats on most of our valves (some are over designed). Likewise, other valves from other valve manufacturers if they are building to the same standards will also have their seats lift or open.
RE: Valve passing at site
gerhardl(Mechanical)
12 Jun 08 08:30
I will echo the previous posts for EN standards and confirm the viewpoints presented.
There is always a limit to what the valve manufacturor will allow as maximum for a valve at a line test. This is partly given by the valve standard, wich will be higher for the housing (open valve housing test 1,5 times pressure class (or more depending on pressure class, dimension and producer and valvetype)) than the seat (operating pressure equal to pressure class normally 1,1 times (again also depending on valve type - for instance will often smaller valves (ball valves for instanca) over-qualify) on allowed seat pressure.
Under line pressure tests there is always a risk of something malfunctioning and giving water hammer, which in addition to overpressure of seats can damage (permanently) the valve sealing or valves.
Generally: blinds should be used and all valves be left open under line tests.
Or (the world is not always ideal) if valves are closed under line-tests, all care should be taken, the valve manufacturor to allow in writing the given pressure.
Two buts: For some types of resilient seated gate-valves for instance, a somewhat higer seat pressure will have less impact than for other constructions.
Secondly: anything going wrong and valves not operating properly or leaking after a (too high) test the responsibillity and guarantee that everything was done properly lies on the test executing side.
I will echo the previous posts for EN standards and confirm the viewpoints presented.There is always a limit to what the valve manufacturor will allow as maximum for a valve at a line test. This is partly given by the valve standard, wich will be higher for the housing (open valve housing test 1,5 times pressure class (or more depending on pressure class, dimension and producer and valvetype)) than the seat (operating pressure equal to pressure class normally 1,1 times (again also depending on valve type - for instance will often smaller valves (ball valves for instanca) over-qualify) on allowed seat pressure.Under line pressure tests there is always a risk of something malfunctioning and giving water hammer, which in addition to overpressure of seats can damage (permanently) the valve sealing or valves.Generally: blinds should be used and all valves be left open under line tests.Or (the world is not always ideal) if valves are closed under line-tests, all care should be taken, the valve manufacturor to allow in writing the given pressure.Two buts: For some types of resilient seated gate-valves for instance, a somewhat higer seat pressure will have less impact than for other constructions.Secondly: anything going wrong and valves not operating properly or leaking after a (too high) test the responsibillity and guarantee that everything was done properly lies on the test executing side.
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