Dear All,
Can anyone answer my below query.

A valve made of SA 352 LCB for low temperature service. Theoritically Impact tested and absorbed energy shall be 18 Joule.

But after hydrotest and painting, valve has been exploded and a test specimen was cut from the body and tested for Impact testing, but resulted that absorbed energy is very less(1/3rd of theoritical).

What is the reason for this.

Any guideline for impact testing after farication of an item.

Anyone answer my query please.

Hello Jayavel

There could be any number of reasons why the valve body exploded. You can tell a number of things by a simple visual examination of the valve pieces. You have to determine if the failure were a brittle or ductile failure. It the edges of the pieces broke at very near 90 degrees, you have a brittle fracture. A ductile fracture will have an approximate 45 degree fracture face. You must also establish the temperature at which to valve failed. Remember, if the safety valve were blowing down a large vessel it could ice up from the adiabatic expansion of the gas.

Let us now consider the result of the impact test of one of the remaining pieces. If the testing machine were calibrated, then the results are verified. The next thing to consider, is what temperature was the test conducted at. The material specification (ASME Section II - Part A) will tell you this. The material should have already been impact tested.

Finally you should do a material trace audit. If the valve conformed to a designated specification, it should carry a name plate with all the details. You will have to go back to the manufacturer of the valve and get the material documentation for the valve. The MTR (Material Test Report) should give you the chemical and mechanical properties.

Finally, you could send a piece of the valve to a reputable laboratory to check that the material is indeed SA 352 LCB. Make sure the lab has calibrated equipment and a quality assurance programme.

The is really using: Root Cause Analysis. It is not rocket science, but it leads you to the cause.

Remember to document each step.