Testing standards: no one-size-fits-all
Today, more than ever before, testing is extremely important in the valve industry. The increase in globally sourced products and muchreduced domestic manufacturing has caused every actor in the valve supply chain to request and require more testing.
^ The pressure safety valve (PSV) is a direct, spring-loaded pressure-relief valve
Article By Adnan Ilyas
This article provides you with information about the inspection of valves and valve testing in the manufacturing shop as well as in operational plants.
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 industrial valves, pipeline valves, control valves and pressure-relief valves, which will be detailed below.
A well-known standard is the shell test or body test, which is performed after successful completion of the valve’s individual components e.g. seat, disc, body, stem, etc. inspection, and assembly. The test is conducted by the valve manufacturer or a repair service provider and based on the requirements of API STD 598 or other relevant standard (Valve Inspection and Testing).
As specified by the above standard, 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.’
Valve seat leak test
The seat leakage (closure test) is performed after successful completion of the valve shell test (body test). One side (valve in- 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 that if valve inlet is pressurized, the amount of leakage in the outlet needs to be measured. A limited amount of leakage is permissible. In the same manner, you have to test and inspect both sides. Note that some valves have only one seat whilst others may have four seats as per their respective types. Test pressures are determined according to ASME B16.34.
Valve backseat test
The valve backseat test is performed in the valve with a backseat feature. This is a feature that allows possible replacement of the valve packing while in 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.
The pressure safety valve (PSV) 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.
PSV – CDTP test
In a cold differential test pressure (CDTP) test, the safety valve is mounted on a test rig.
Adjust (raise) the nozzle ring 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. A POP-test needs to be repeated a minimum of three 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 size of the valve.
PSV – seat test
In the seat test, the operator raises the pressure up to 90 per cent of the CDTP and observes the leakage at the outlet of the valve 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.
Bellow integrity testing
This test is performed for Safety Relief valves which contain a bellow feature. Main function of this feature is to deal with back-pressure effects caused by different outlet situations. For such valves, it is mandatory to perform verify bellow integrity. To check the bellow, approximately 1 to 2 bar pressure at the outlet of the valve needs to be applied and one needs to observe leakage from the vent which is situated in the bonnet. No leakage is allowed.
In the shell test for a conventional safety valve, one has 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 valve, the same pressure is to be applied at both outlet and bonnet vent. Leakage observing points are the same which are mentioned above
Third party inspection (TPI) guides you through all the necessary stages in the production of the valves, from the examination of certification of procurement sources to the final inspection, preservation, and packing, to the dispatch to site.
The following activities are addressed during TPI:
• Valve material inspection
• Valve welding inspection
• Visual and dimensional checking
• Valve low pressure air test
• Valve hydrostatic testing
• Post hydrostatic testing
• Valve final inspection
• Valve name plate checking
• Valve painting and coating checking
• Valve spare parts, loose items and accessories control
• Valve packing, marking and shipping inspection
Valve testing techniques have definitely changed over the years in terms of testing tolerances, criteria for valves and many other factors proposed in the form of new editions of standards to enhance performance and work quality. To improve the performance of a plant, it is essential for everyone working in this field to ensure that the right techniques with enough knowledge and mandatory safe work procedures are being followed.
About the author
Adnan Ilyas works as a Valve Maintenance Supervisor and is currently employed with Saad Al Essa Group (KSA) (TPI of Saudi Aramco and others). He holds a Electronics Engineering Diploma from PBTE Pakistan. He has nine years of professional expertise in inspection, maintenance, testing and installation of variety of valves in the oil and gas industry.