WELDED HALF-PIPE JACKETS; LEAKING 1

[mdboh]

I am looking at a non-maintainable half-pipe coil jacket on a pressure vessel operating for up to and over 40 years. What kind of leakage problems will occur and is there methods to quality these welds prior to operation to ensure a 40 year life.

Thanks

 

[Shahin71]

What will be the flowing medium,is it cooling water or
steam?

We used to have this type of coils "we call them limpet coil" on a reactor for cooling,they failed after three years although they were SS 304 , we had to switch to internal cooling coil.Failure took place due to cracks in welding joints and then in the pipe it self,this happened for 2 reactors of 15 m3 capacity.

Mechanically ,limpet coils are normaly subject to high thermal stress if they are not allowed to expand ,contract freely which is difficult to provide.

Regards

Shahin71

 

[mdboh]

It is chilled water that we will be using to cool the vessel contents. Is there any way to qualify the welding to ensure that it doesn't leak?

 

[Shahin71]

Of course you can do the ND Tests which are usually done for such works , you can do radiography test,magnatic particle test,ultrasonic test...

Main thing is to be sure that the coil will not be subject to high thermal stresses


Good Luck

Shahin71

 

[MJCronin]

mdboh,

"Half-pipe" jackets are most often specified where the vessel will udergo both heating and cooling cycles. The are more expensive than the adhesively bonded "dimple-jackets" which are also in use in the CPE.

"Half-pipe" jackets are subject to thermal cycling stresses and will eventually crack. The degradation of jacket life is directly related to the number of thermal cycles and the range of temperature in each cycle. When live steam is used to heat the jacket, hot spots can occur which will locally suject the vessel to high thermal stresses and reduce the useful life.

Most "half-pipe" jackets are schedule 10S stainless steel and are from fabricated from piping 2 to 3 inches in diameter. The description of the weld between the half pipe and the vessel shell is (somewhat)up to interpretation. Some fabricators call this weld a fillet, others refer to the weld as a "full-penetration".

The fact of the matter, is that this type of welding is difficult to perform and inspect. SHAHIN71 is both wrong and misleading in telling you that a variety of NDE is commonly available.

Radiography is not possible due to the geometry of the jacket. Mag-particle testing cannot be done on austenitic stainless materials and UT, I believe, is very difficult due to the adjacent coil........ This leaves us with Visual Ispection and hydrotatic testing of the coil. Some vessel fabricators (ROBENS of New Jersey) will offer borescope internal visual inspection of the jacket welding.

The ASME vessel vendor with the most experience and jacket welding quality is NOOTER of St. Louis. They have a Dr. Jaawad who has written an appendix to the ASME code about half-pipe jackets. Also try "Modern welding" of Owensboro Kentucky.

If you are going to use the jacket for cooling only, you should have a long usefull life. Insist on weld inspection records of the jacket and ask about the additional cost of a "premium" welding job.

Hope that these comments help....

MJC

 

[Shahin71]

MJC

Possibility of doing radiography depends on the inspection company and we have done this before,I think mdboh should get the advice from a specialized company to recommend the possible way. Same thing can be said about ultrasonic.

It is known that mag.test is not suitable for Aust.St.St but the question did not mention St.St,it is general.




Shahin71