Requirement to pressure test process vessels during service life? 1

[DefenderJ]

We have a number of ASME VIII Div1 pressure vessels that have seen 28 years service. Fabricated from ASTM A516 Gr 70. Also several possible degradation mechanisms.

Some of these have been hydrostatically tested after modifications.
However there are several that have had no test since construction as no mofications have been carried out.

Are there any industry guidelines on the need to test a pressure vessel after a certain age?
API 510 5.8.1.1 indicates the need to conduct a test as depending on whether it has been modified or if the inspector believes one is necessary.

Our legislation does not require anything specific other than an insurance inspection to visually examine every 26 months

And thoughts and advice would be welcome.
Thanks

 

[SJones]

http://www.hse.gov.uk/research/rrhtm/rr729.htm

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[normet]

Steve,
Unless you have major work done to the pressure envelop ( through wall construction), a hydro test is not warranted. The ASME test requirements are really only a leak test. You could jeopardize the structural integrity of the vessel foundation, vessel support, or the vessel itself by doing a hydro after the equipment has been in service. The important thing is to have regular inspections and API 510 is a good guide.

There are other options to hydro testing even after a major repair - see the options in B31.3 which are restated in PCC-2 for vessels.

 

[metengr]

The need for pressure testing is based on regulatory requirements first and foremost. If no regulatory requirements are specified, pressure testing does nothing other than find leaks. Pressure testing does nothing to predict or ensure long life of a vessel. The above was introduced into the NBIC about 8 years ago.

If you need to rely on pressure testing for condition assessment this is the wrong reason for testing. There are NDT methods and condition assessment practices that far outweigh reliance on pressure testing.

 

[DefenderJ]

Thanks Steve.
This is useful - the HSE does have some good stuff.
I see a lot of this report is based around RBI and is more about inspection that hydrotest.
A hydrotest would actually being easier and quicker than NDE for us.
Before RBI are there any guidelines that might be applicable?

 

[DefenderJ]

This thread is running so fast I can't keep up.
Thanks for the input everyone.

The position I am in is that we currently have exceedingly little proof of vessel condition. We do not appear to require any more than we currently have with a insurance inspector inspection. A hydrotest would be something we could easily acheive and has been suggested by one of our engineers. This would "Certify gross structural integrity" as ASME PCC-2 would put it.

Internal and external inspection would be very expensive and time consuming and I cannot get support for even limited internal inspection of welds. As inspection is difficult it makes RBI look difficult apply.

By the way our process is Alumina refining and thus we have very little in the way of standards which are specific to our service and operation.

 

[metengr]

DefenderJ

Internal and external inspection would be very expensive and time consuming and I cannot get support for even limited internal inspection of welds.

The insurance inspector should be performing detailed internal/external inspections of this vessel per Part 2 of the NBIC on a Jurisdictional requirement basis or per your insurance company requirements. There are requirements for type and method of internal/external inspections in the National Board Inspection Code (NBIC).

 

[puigi]

Hydrostatic testing is not warranted unless you are performing a repair or alteration. I would not rely strictly on a satisfactory hydro-static test as an indication for indefinite continued service life.
Internal inspection frequency is determined by the service conditions and corrosion rate. An internal inspection looking for some of the possible degradation mechanisms you suspect, along with either mechanical or volumetric NDE (UT) testing of the vessel wall at multiple locations to determine the corrosion rate is necessary in order to determine remaining service life.

 

[adamuk]

I remember reading some work carried out by the British Gas research bods in Newcastle UK about 15 years ago. They were looking at the effects of hydrotesting underground piping with small, deep pits. One of the results was that piping undergoing hydrotesting failed at a subsequently lower pressure due to deformation of the corroded area (they termed it a 'reversal').

Thus not only is pressure testing no proof of fitness for service but can also, if you have in-service deterioration, cause premature failure. There's no substitute for a good visual examination supplemented with NDT. As a UKAS accredited inspection body (i.e. licenced to carry out legally-mandated inspections in the UK) that is also our approach.

If I have time I'll dig out the papers but they're buried in an archive somewhere.

Adam Potter MEng CEng MIMechE

http://www.ax-ea.co.uk

 

[MJCronin]

Interestingly, periodic hydrotesting is strongly suggested for cross country pipelines subject to cyclic fatigue.

http://www.kiefner.com/downloads/apifatigue.pdf

After the recent San Bruno pipeline accident, where eight adults and children were burned alive, PG&E decided to implement a segmenet-by-segment hydrotest of thier system.

http://www.pge.com/myhome/edusafety/systemworks/gas/pipelinesafety/hydrostatictesting/index.shtml

So, by analogy, I would suggest that periodic hydrotesting should be considered for pressure vessels subject to many cycles of pressure loadings.

I would also suggest that states should require hydrotesting be performed on pressure vessels when they are bought or sold.

It would be interesting to see what the Europeans require of thier vessels in the PED standard.

My opinion only....

 

[adamuk]

Yes, overpressurising a component containing a crack can blunt the crack tip and provide a small zone of compression at that region thus retarding further growth. The pressure required to do this would depend on crack location and geometry.

The PED primarily regards placing equipment onto market rather than in-service fitness for purpose. Many people forget that the PED is a directive to provide trade harmonisation rather than a safety standard. It ensures that any CE marked vessel can be sold in any EU country.

Adam Potter MEng CEng MIMechE

http://www.ax-ea.co.uk