Upper limit of Hydrotest pressure 3

[Ray6]

Sec VIII Div 1 , states "This Division does not specify an upper limit for hydrostatic test pressure", but if there is visible permanent distortion it can be rejected.

My question is in practice how to calculate this limit. Let's say my MAWP is 1000psig. How to calculate upper limit that there is no invisible permanent distortion and also nothing goes ..Boom?

 

[weldstan]

Think about the specified minimum yield strength of the material(s) in your calcs.

 

[SnTMan]

Given variability in material properties I doubt it can be calculated with any reasonable degree of accuracy. I'd think the same issue would cast doubt on FEA methods as well.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Ray6]

@weldstan , For sure, but what percentage of yield/tensile? for example Div2 specifies 90 of yield. Can we use this practice for Div 1?

 

[DriveMeNuts]

I don't understand the premise of your question. If you stick to the minimum test pressure, then "Permanent Visible Distortion" wont occur.

The purpose of the code is to efficiently design equipment and provide minimum pressure test requirements which the vessel is certain to pass if fabricated correctly, and then go on to operate safely.

Your question doesn't relate to the core purpose of the code. I don't understand why you would ask it. Is there a reason why you would exceed the minimum test pressure?

If it is just a question of interest, then the most accurate way of learning how a vessel will behave and distort when the minimum test pressure is exceeded would be to conduct an elastic-plastic analysis of the over pressure test. But even then, knowing if the distortion you can see on your computer screen would be "visible" in a the real world (and therefore a failure) requires real world experience of intentionally failing vessels. After you have failed a few in the real world with "visible distortion", you can perhaps gain the experience to reasonably accurately predict failure on an elastic plastic analysis with out the need to do the real world test.

 

[weldstan]

I do not have ASME VIII, Div. 1 as a resource anymore due to being retired for 5 years, but as I remember ASME I had a hydrotest limitation that no component within the system could achieve a stress during hydro above 90% of the SMYS.

 

[TGS4]

weldstan - there is no such requirement in ASME Section VIII, Division 1. The pre-2007 Edition of Division 2 had a 0.9*Sy limit on Pm - the current Edition of Division 2 has a limit of 0.95*Sy limit on Pm.

DriveMeNuts - there needs to be a range of test pressures between the minimum and maximum.

Ray6 - unfortunately, the Code does not specify what constitutes "excessive" distortion, although it does state that it is the distortion after the pressure test, so after the test pressure is applied and removed. This would be a judgement call on the part of the inspector - therefore I would base any discussions with them.