Leak Detection in Cladded Vessel

[Jaketman]

For cladded vessels, if we were to develop a leak under the clad (say from cracking, local defect, or blunt impact by foreign object of the clad during service), what are some of the things you can do to help identify the leak prior to corroding through the steel? I know vessels are typically designed with tell-tale holes at nozzles, but how about a failure in the clad plate itself? Is there any design for the cladded shell and heads that can be used to provide early detection of corrosion into the steel prior to manifesting a leak? How about NDE or inspection techniques that can be used to catch localized corrosion before it leaks? I am asking this question because typically, cladded vessels are required for cost, but most of the time in these vessels, the steel will readily corrode if exposed to the process. What can you do either from a design or inspection point of view to keep yourself from having a major problem on your hands (especially if early detection is critical, for example, the vessle is under insulation, contains hazardous chemicals, and operates at high temperature and pressure)?

Thank you in advance for your comments.

 

[REGRUMBLE]

During fabrication of clad vessels we always do UT inspection for any separation or suspect areas. Depends on the size of the vessel but 100% UT if it is insulated or filled with hazardous chemicals may not work. UT may also reveal how much clad is left for areas where it is wearing thin.

 

[weeeds]

If you are using a liner then you can drill a hole through the steel from the outside and pull a vacuum on the space between the liner and steel. You can connect a vacuum gauge or sensor to this space and then mintor any decay in the vacuum. Using this technique you can also use Helium Leak Testing to locate any defects in the liner should you witness a vacuum decay.

 

[r6155]

Acoustic Emission Examination (AE) may be useful.
1) AE during hydrostatic presure test -new vessel-
2) AE during in-service inspection

My opinion only

Regards

r6155

 

[Jaketman]

Thanks for the constructive replies.

The liner idea makes sense, but with my experience with loose liner failures, I don't want to create a higher susceptability for leaks in order to detect them.

We typically standardize in explosion cladding.

r6155 -- Is acoustic emmission appropriate for monitoring continued corrosion. I thought it was more appropriate to detect crack propogation (by increasing internal pressure conditions). Can this technology be used for a small break in the clad (i.e. pinhole defect) to measure corrosion?

Another question is can leak detection be addressed with vessel design. For example, tell tale holes are installed at nozzles, but can something on the same lines be used under the clad? Perhaps the steel substrate can be channelled or sectioned to allow any leakages to make their way to pre-drilled leak holes. Anyone even heard of something like this being done or how to do it?

Thanks again for your help!

 

[r6155]

Jaketman

With Acoustic Emission (AE) you can detect a lot of imperfections and defects.

Please, contact any company of NDE in your country for more information about AE.

Regards

r6155

 

[SJones]

Of course, there are non-intrusive NDT techniques that will work, but how much of the vessel will you need to inspect, how often, how reliable is it and how much will it cost. These are the key questions. There may be no option but to keep going inside the vessel.

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

Steve Jones
Materials & Corrosion Engineer

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

 

[weldtek]

It sounds like surface inspections at regular intervals may be your best option.

 

[Duwe6]

Regular Internal Inspx using the services of a certified API-510 Inspector. An experienced Inspector can find most leak-under-clad using a flashlight and a small hammer to 'ping' the cladding. Inspector will then take UT readings at anomolus areas he finds. This will need to be done every 1-3 years, so that leaks behind the cladding have not had time to destroy your vessel. If a pinhole leak can corrode through your shell in 3-4 years, then your Inspection interval needs to be half that, or less: 1-2 years.

What with the cost of the Inspector, and the preparations it takes to make a vessel ready for human entry, and the fact that these Inspx will need to be done every 1-3 years; explosion clad or weld overlay now look pretty cheap.