Test and re-certification of ASME VIII Division 3 pressure vessel

[TommyBye]

Hi,

We've got some 100 gallon / 17500 psi (rated) pressure vessels which are used for cyclic loads. Typically the a vessel is pressured up and kept pressurized for 2 hrs at a time. When in use they typically see about 5 cycles every day. Approx 100 days of use every year --> 500 cycles/year. Oldest vessel is approx 20 years --> 10,000 cycles (high estimate, actual could be less than half)). Operational pressure is 10k PSI. The pressure vessels are pressure tested to 1.43 x design pressure regularly.

Due to the pressures used and number of cycles we've had some discussions on what the requirements for re-certification are. I've checked the standard but I can't find any requirements for neighter pressure testing nor re-certification (full inspection + NDT). Does anyone know the actual requirements and which standard I should use for testing/re-certification?

Thanks in advance!

 

[DriveMeNuts]

There are no set rules that I am aware of. IT depends on the equipment and potential hazards. For a low pressure vessel, a thorough NDT inspection of individual components on a vessel at 50%, 75%, 90% and 100% of the fatigue life of the individual component is reasonable. Where any cracks occur, get the fracture mechanics expert in.
For high pressure and hazardous equipment, the testing starts sooner. Perhaps 20, 40, 60, 70, 80, 90, 95 and 100%.

I'm a little surprised that you are "regularly" pressure testing to 1.43x 17500 PSI.
A single pressure test cycle of this would cause the same amount of fatigue damage as a years worth of general operations (500 cycles of 10000PSI).
My advice would be to go away and look very closely why you are "regularly" pressure testing the aquipment. Someone may correct me on this, however a pressure test is typically only done once at the beginning of its life to confirm protection against plastic collapse and to give any residual stresses a good work out. A second pressure test may be done if the equipment has been sitting dormant at the back of a yard for many years collecting rust. Testing a vessel to see if it is protected against fatigue actually damages the vessels fatigue life massively.

You will need to have a look at the fatigue calculations, and if they don't include the effects of the regular pressure testing, then they need to be amended.

You can re-certify non-fatigue vessels. You can't re-certify fatigue vessels once they reach the end of the calculated fatigue life. If you have accidentally gone past the 100% mark, then you are naughty and need to be doing extreme risk-based monitoring for cracks while you get a replacement vessel. If the vessel fails before the 100% mark then you are fine. If the vessel goes pop while passed the 100% mark, then how are you going to explain this to the court judge?

Vessels are often designed for double or triple the intended design life to avoid the need for the periodic inspections mentioned above or where it is not possible to get access to inspect.

 

[XL83NL]

A bit off topic perhaps but is this vessel subject to the pressure equipment directive 2014/68/EU? I noticed the 1.43 factor the pressure test.

Huub