End Caps for Hydrotesting

[RauMech]

Hello.

My question is, we are using end caps for hydrotesting for over a period of time. Not sure how many times these end caps were been used over the years. And supposing that those are not been tested over the allowable test pressure limit, how many times we can use these? Is there a restriction or check that needs to be done for the repeated use of these end cap?

Thank you
Rau

 

[bernoullies123]

There shouldn't be any restriction on the usage.

Checks yes.
You should have the documentation associated with each cap. If fabricated, then the design calculations should be accessible. Perform appropriate inspections, visual and MT/PT as a minimum. If unaware of their past usage, suggest UT some joints to ensure integrity.

 

[DSB123]

bernoullies123,
So you are saying that the end caps are OK for say 12 million cycles of pressure loading up to the test pressure!!!!

 

[blacksmith37]

Are they threaded or flanged ? When testing OCTG casing ,the cap threads get damaged long before a fatigue life end. For a flanged test cap, it could be made much stronger than the test parts.

 

[bernoullies123]

DSB123,
Not explicitly no. With most end caps as well as in this instance, the number of cycles are never know. I would put it down to a bit a common sense and reason. Of course there is always the fracture mechanics associated with high frequency cycles but if it appears it has been used and the associated evaluations concluded that it is of sound product then I don't see any reason for not using the product for its intended purpose.

Now I am not aware of any specific requirement on the maximum number of usages of an end cap, and believe it comes down to individual risk assessments and engineering judgement.

 

[DSB123]

bernoullies123,
It was just that your opening response was "There shouldn't be any restriction on the usage." which could be misleading to those who do not understand fatigue damage.

 

[Duwe6]

Assuming mag-particle - MT testing every 50 uses, after the first 500 uses, I'd park my favorite car in front of that cap for every hydro. Weldcaps are immensely strong. Most hydros will not stress a cap enough to count as a fatigue cycle.

 

[gr2vessels]

My two cents, and my car too.
Since when the fatigue became a such big issue for a test cap? So what if fails, you have to take all the precautionary measures anyway. When fails, bad luck, replace it with a better one. 12 million cycles are 12 million hydrotests, one hour each plus fabrication one day, you're not going to live to see if you are right or wrong...