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Valve Inspection And Testing Overview

Views: 52     Author: Site Editor     Publish Time: 2023-03-10      Origin: Site

Media flow hydraulic processes and procedures are heavily dependent upon quality valves. Failure in a piping system from faulty valves can incur considerable and costly damage. In some cases, these failures may risk catastrophic property damage or injury and death to workers.



Because of the critical role valves have in complex and intricate processes, proper inspecting and routine testing should be part of a risk mitigation plan. Today, we’ll go over the kinds of valves, industry standards, and testing you might encounter.


Valve Inspection And Testing Overview_1



butterfly valve inspection


What is a valves?

While the function of a valve is relatively simple, the designs are diverse and sometimes complex. Below is a list of valves you may already be familiar with along with their applications.



butterfly valve – A quarter-turn valve used to control the flow of liquid, gas, or particulate matter. It is used in treatment plants, food industry, ship industry, petrochemical plants, fire extinguisher systems, paper manufacturing, and many more applications.


Ball Valve – A shutoff valve with a rotary ball controls flow and pressure control in gas distribution systems as well as pressure reduction in connection with gas storage. It is used in applications involving corrosive fluids, slurries, or normal liquid and gases. Applications are found in the oil and natural gas industry, manufacturing sectors, chemical storage, some residential uses, etc.


Globe Valve – A linear motion valve used to start, stop, and regulate flow. It may be used for isolation and throttling. Applications include cooling water systems, fuel oil systems, feedwater or chemical feed systems, turbine lube oil, boiler, and main steam vents or drains.


Check Valve – A one-way, non-return valve where the flow runs freely in a single direction and works to prevent backflow. It is used in pumps, fluid systems (for chemical and power plants), and more.


Needle Valve – A plunger valve with a small opening (or port) that has a needle-shaped plunger that allows precise regulation of flow. It’s ideal for systems with lighter and less viscous media with low flow rates or systems with small channels and pipes. This valve regulates gas or water through an appliance or system.


Gate Valve – A sluice valve that is multi-turn and works by inserting a rectangular gate or wedge in the path of a flowing media. A threaded stem connects the actuator (such as a handwheel or motor) to the gate’s stem. It is found in industrial applications such as pharmaceuticals, manufacturing, automotive, oil and gas industry, or marine. It’s also useful in underground applications and is ideal for vertically-oriented setups (as it is space-saving).


Pinch Valve – A full bore or fully ported valve that “pinches” to obstruct the flow of fluids. It’s used for liquid, solid, and slurry applications. It’s ideal for isolating or regulating media that is abrasive, corrosive, and fibrous.


Plug Valve –  A quarter-turn rotary motion valve where a tapered or cylindrical plug is used to start and stop the flow of media. Applications include natural gas piping systems, oil piping systems, coal slurries, mineral ores, mud, sewage, or vacuum to high-pressure applications.


Pressure Relief Valve – A safety relief valve designed to open at a preset pressure level and discharge fluid until an acceptable level of pressure is reached. It is necessary for applications where pressure levels are critical (such as oil and gas, petrochemical, or power generation using steam, air, gas, or liquid). Applications include firefighting, high-rise building systems, water towers or tanks, drinking water systems, or multi-phase applications in refinery and chemical processing systems.



Valve Shell Test


3-Piece Trunnion Mounted Ball Valve while testing

Shell Test or Body test is performed after successful completion of valve individual components e.g. seat, disc, body, stem, etc. inspection, and assembly. The test is conducted by valve manufacturer or a repair service provider and based on the requirements of API STD 598 or other relevant standard ( Valve Inspection and Testing).



The valve shall be partially open and be able to hold pressure for a certain time. The pressure shall not be less than 1.5 times of maximum working pressure. No leakage is allowed. Leakage check points are body, bonnet, stem, plugs/fittings and flange connections.



valves Seat Leak Test

The Seat Leakage (Closure Test) is performed after successful completion of the valve shell test (Body Test). One side (valve inlet or outlet) shall be subjected to the hydrostatic pressure and amount of leak shall be measured on the opposite side of the valve.



It means if you are pressurizing valve inlet, then you have to measure the amount of leakage in the outlet. The limited amount of leakage is permissible.  In the same manner, you have to test and inspect both sides. Though valves have only one seat or other may have 4 seats as per their respective types. Test pressures are determined according to ASME B16.34.



Valve Back Seat Test

The valves Back Seat Test is performed in the valve with a backseat feature. This is a feature that allows valve packing being replaced while it is in the service. In this test, the valve shall be fully opened and packing gland shall be loose or not installed. No leakage is permissible in the backseat test. Keep in mind that the test pressure for the backseat is same as the other seat test of the valve.



Pressure Safety Valve Testing

The pressure safety valves is a direct, spring-loaded pressure-relief valve that is opened by the static pressure upstream of the valve and is characterized by a rapid opening or pop action.



When the static inlet pressure reaches the set pressure, it will increase the pressure upstream of the disk and overcome the spring force on the disk. The fluid will then enter the huddling chamber, providing additional opening force. This will cause the disk to lift and provide a full opening at minimal overpressure. The closing pressure will be less than the set pressure and will be reached after the blowdown phase is completed.



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Cold Differential Test Pressure (CDTP) Test: In this test, the Safety valve is mounted on a test rig. Adjust Nozzle ring (raise) to -2 notch position (Gas trim Valve). The operator applies the pressure (As per valve specification and data sheet) at the inlet of the valve. A safety relief valve pops or releases pressure when it reaches the desired set pressure. POP Test (to be repeated a minimum of 3 times to identify consistency). A reseating pressure shall be noted and recorded. In the industry, for this type of test, the standard which is widely followed is ASME Sec VIII Div.I. Test passing requirement and acceptance criteria are described as per the size of the valve.



Seat Test: In the seat test, the operator raises the pressure up to 90% of the CDTP and observes the leakage at the outlet of the valves for a particular period of time. Acceptance criteria in bpm or meter cubic feet are described in API-527 standard based on size and testing medium.



PSV Back Seat Test: Safety Relief valves which contain a balanced bellow to overcome the back pressure which is caused by different outlet aspects. For such valves, it is mandatory to verify bellow integrity. To check the bellow you have to apply approx. 1 to 2 bar pressure at the outlet of the valve and observe leakage from the vent which is situated in the bonnet. No leakage is allowed.



External body or Shell Test: In the shell test for a conventional safety valve you have to apply 100 PSIG / 7 Bar at the outlet of the valve and then observe leakage at different connecting points such as body/bonnet joint, nozzle/body, nozzle ring adjustment lock and the stem opening on top. But for the body test of a balanced type valves, the same pressure is to be applied at both outlet and bonnet vent. Leakage observing points are the same which are mentioned above.



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