It is not uncommon for certain applications that a new type of valve will have to be developed to meet the end user’s needs. Most end users have the highest technical demands on valves they are aiming to use in an assembly. Needless to say these ‘prototypes’ will undergo extensive testing to verify reliability, safety etc. TAT (Shell MESC SPE 77/300) is one of the internationally recognised certifcation to ensure the quality of the valves. 

TAT is done as per  ‘Shell’  specification 77-300 in which the valve is subjected to seat test, fugitive emission test, and torque test under pressure, during and after mechanical and thermal cycling. The qualification range is mentioned in spec 77/300B.

It is testing that is done to a product to confirm the design is good. It is a product performance test which is different from FAT (Factory Acceptance Test), which is done to verify the quality of the product comming out of the factory.

In short, TAT = DVT = design verification testing
and FAT = Verfication of production quality