What is the procedure for a valve test?

Valve Testing – Hydrostatic, Pneumatic, Shell, Seat, Fire...

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Valve Testing – Hydrostatic, Pneumatic, Shell, Seat, Fire…

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.

Generally, valve testing simulates operating conditions in a controlled environment to ensure valves are fit for service. 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 a valve might 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, usually water with a corrosion inhibitor. Technicians then apply pressure over a specific period. The time and level of pressure vary 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. The procedure also varies depending on the type of valve. Generally, pressure tests aim to ascertain the integrity of the valve shell, seat, and seal against leakages due to pressure. 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 and test standards.

Common industry guidelines for pressure testing valves can be found in ASME B16.34, API 598, MSS-SP-61, API 527, and ISO 5208. Many tests are recorded on paper wheel charts or manually, although digital options are becoming more prevalent.

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 is the preferred medium. Generally, hydrostatic testing is ideal for high-pressure applications where the equipment is not moisture-sensitive.

In situations where moisture can damage equipment—usually via corrosion or by altering the chemical balance in the system—pneumatic testing is recommended. Industry guidelines recommend using pneumatic testing for cryogenic and low-temperature valves because removing all water after the test is difficult. 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 straightforward 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 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 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. Its testing in the industry is driven mainly by guidelines from API 598 and ASME B16.34. Typically, the valve is mounted on a test bench and partially opened. The shell is then pressurized, with ASME B16.34 recommending a minimum of 1.5 times the valve pressure rating at 100°F (38°C) for hydrostatic testing. Pneumatic seat testing is done to 80-100 psi. Both API and ASME standards recommend varying test durations depending on the size of the valve. 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 ≤ 30.0 300 Valve Size vs. Test Duration for Shell Test

The test water temperature should range between 41°F (5°C) and 122°F (50°C). The pressure gauge used for measurements should have a 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. The same API and ASME standards as the shell test provide guidance. The recommended pressure is 110% of the maximum allowable pressure at 100°F (38°C), 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 ≤ 30.0 120 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 48 8.0 ≤ 12.0 20 40 14 and above 2 drops per minute per IN 4 bubbles per minute per IN

For valve sizes greater than 14 inches, the hydrostatic test leakage rate should not exceed two drops per minute per inch. 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 reliable fire protection, particularly for sensitive applications such as oil and gas, refinery, and petrochemical industries. 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 subjected to high-temperature flames between 1382°F (750°C) and 1832°F (1000°C) for a period of thirty minutes. During this period, the heat intensity and the leakages—both internal and external—are monitored and measured. After extinguishing the flames and allowing the valve to cool, technicians test its pressure-retaining capacity. Throughout the test, the leakage levels should be within acceptable limits for the valve to pass as "fire-safe". Some key things to note about fire testing include:

• Leakage from the piping to valve end connections is not part of the acceptance criteria.
• Technicians measure temperature 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 10497, BS 5146, and BS 6755 constitute industry guidelines for fire testing. Several companies establish their bespoke procedure for fire-safety valves based on these guidelines. Among these 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 occur anywhere along the piping system, statistics show that approximately 60% of fugitive emissions stem from valves. This data highlights the importance of this test. 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 workers and nearby communities.
• Environmental damage.

During fugitive emission tests, the most common test gases are helium and methane. The valve is pressurized with the test gas at varying temperatures, and technicians monitor for leakages via the sniffing or vacuum method. International standards such as API 622, API 624, API 644, ISO 15848-1, and ISO 15848-2 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 performed 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 down to -320°F (-196°C).

Helium then pressurizes the valve to the operating pressure specified for its class. During the test, technicians closely monitor the temperature inside the valve and any leakages. At the end of the test, the valve is depressurized and warmed up until it attains ambient temperature. A detailed report then 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 28921-1, ISO 28921-2, EN 12567, and BS 6364.

In addition to the standards mentioned in the previous sections, several others 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 reference.

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 steel valves larger than NPS 24 inches. Flanged, threaded, and welded end 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 5208, and MSS SP61 Hydrostatic testing of valves. FCI 70-2, ISA S-75 Control valve testing. Standards for Valve Testing

Valve Testing and Inspection in Quality Control Explained

Quality inspections and valve testing are extremely important for the smooth running of fluid systems. Industrial valves are an integral part of many industrial machines, and even the tiniest malfunction can have a ripple effect on the rest of the machine. Therefore, it's important to carry out the right checks to ensure safety and efficiency.

When it comes to testing valves, multiple valve testing procedures must conform to strict acceptance criteria or performance standards. In this article, we’ll go through the key things you need to know about valve inspection procedures and tests.

What Are the Common Types of Valves?

Valves come in all different shapes and sizes depending on their industry or application.

These are the most common types of valves:

1. Butterfly Valve
2. Gate Valve
3. Globe Valve
4. Gray Iron Valve Body
5. Gray Iron Valve Cover

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6. Plug Valve
7. Swing Check Valve

The Importance of Valve Testing

Valves need to conform to certain leakage standards, and various other checks are also carried out. Valve testing and inspections should ideally be done every 12 months or so to ensure they are still in the best working condition. However, this will vary depending on the age of the valve, the condition of the valve, and the type of valve in question.

How Do Valve Leakages Happen?

Valve leakages are a common phenomenon that can happen for many different reasons. There are two primary ways a leak can happen in a valve: fugitive emissions from a valve escaping into the atmosphere and leaks escaping through the valve but remaining contained within the piping system.

The first can naturally damage the environment and become a potential safety hazard to people. Valves are considered to be the major reasons for fugitive emissions being lost, so quality management and testing of valves are important.

What Are the Common Causes of Valve Leakages?

Valve leakage is a common problem in most industries and can be caused by various factors. The most common causes include a valve not being fully closed because the valve seat is being prevented from closing due to dirt, rust, or line debris; insufficient actuator travel; or a damaged valve seat. Naturally, other factors could cause leakages, and testing will check for all of these potential issues.

What Are the Common Reasons for Leaks Into the Atmosphere?

The reasons for potential leaks into the atmosphere could include the gasket between the valve body and valve bonnet being damaged or the stem packing being out of place, worn, or damaged in some way.

What Is Valve Testing?

Valve testing is a process used to test and evaluate the health or condition of an operational valve. Naturally, there are many different types of tests and inspections performed on valves to ensure they are in the best condition and safe for use.

What Are the Valve Testing Procedures?

A typical testing procedure for a hydrostatic valve might involve the following stages:

• The body of the valve gets filled with testing fluid at a certain temperature.
• Pressure is applied for a certain length of time (usually for at least one minute).
• The leakage is measured across the element of interest of the valve such as the stem, seat, or closure mechanism, using physical instruments while being visually inspected.
• Finally, a valve should have a final visual inspection to check if it was damaged during the testing process.

What Are the Main Valve Leakage Tests?

Here is a list of the most common types of tests carried out to check for valve leakages and the types of valves associated with them:

Valve Seat Leakage Tests

The valve seat tests procedure involves placing a valve under pressure, then measuring the amount of leakage on the other side of the valve. The test pressures are often determined according to the American Society of Mechanical Engineers (ASME) B16.34.

Back Seat Tests

Valve backseat tests are commonly conducted on valves that have a backseat element, such as the gate and globe valve types. The back seat tests are performed according to the approved test procedure, but they often involve opening the valve while the packing gland is loose or not installed.

Valve Closure Tests

The closure test is typically conducted on valves that are used in fully closed and fully open service. These kinds of valves include, but are not limited to, stop valves, globe valves, plug valves, and ball valves.

Shell Leakage Tests

Valve Shell Leakage Test helps identify the presence of water and other fluids in the valve casing. The test is conducted by pressuring the valve for a specified amount of time, usually one minute or more, and looking for leaks. They are performed on valves like check, stop, and isolation types.

The Types of Valve Testing Standards

Below is a breakdown of some of the most common valve testing standards:

• API 598: Valve Inspection and Test

• API 527: Seat Tightness of Pressure Relief Valves

• ASME B16.34: Valves – Flanged, Threaded, and Welding End

• AS