API 5L grade X-52 to be welded to API 5CT grade K55

[B777300]

In the field, surface casing of API 5CT grade K55 is corroded. It is proposed to weld API 5L grade X-52 onto the casing material over the corroded areas thereby covering the corroded areas. I need a welding procedure for this repair. I have consulted a welding engineer who responded that 1) "repair welding of grade K55" would "not be permitted" referring to API Spec 5CT section 9.16, 2) the microstructure is a tempered martensite and 3) only the mill could give me a welding procedure. Now I am sceptical about this advice. I interpret API Spec 5CT section 9.16 as applying to couplings - which are not allowed to be welded anyway - and not to the casing body.

Does anybody out there know whether welding these two materials together would be feasible? Thank you for your thoughts in advance.

 

[metengr]

B777300;
As I started to read your post, not as an expert in API codes but more from a practical view, I became concerned that you are proposing to band aid the corroded section of the casting. If you can weld to it, why not overlay the corroded section?

 

[SJones]

It doesn't matter what API 5CT says as that is a purchase and supply specification; yours is a maintenance scenario. What exactly is the nature of the corrosion? External or annular? If it is external, do you not think that you will be wasting your time with a metallic repair that will corrode again? Also, will it be an in situ repair because you will probably be having to do some serious heat treatment (provided that you can still keep the required mechanical properties of the K55 after welding in the first place)? I would investigate a GRP repair method such as Clock Spring or similar as a parallel option.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[B777300]

@metengr: It is casing - oil country tubular goods, not casting. I am not sure whether you understood casting or not.

@SJones: The corrosion is inside the annulus. Outer casing is 20" K55. Inner casing (the corroded one which needs to be repaired) is 13 3/8" K55. The corrosion at the top is really bad, with large areas "through" the metal. As far as I can gather from the Clock Spring literature (thanks for the tip) this would be too late for such a solution. The idea is to weld 16" X-52 material (half sleeves) to the still healthy lower part of the 13 3/8" K55 casing, thereby restoring the casing integrity for load carrying (for five years or so).

Unfortunately I myself was not involved in diagnosing the corrosion. I have been asked to facilitate getting a welding procedure to weld the two metals together. So, my answers could be limited. There is an entire repair procedure already developed, fixing the holes with Durmetal, etc. My problem now is only welding the two metals together.

The repair will be in-situ (it is on the well-head). Heat treatment equipment for these tubing sizes are available at site. It requires a lot and constant attention, but heat treatment has been done in other in-situ welding repair applications at this particular site before.

API 5CT being a procurement and supply spec and not applicable to repair: - understood, thank you.

Once I know that welding the two metals together is feasible and, perhaps, has been done before, I can get down to get the details of a welding procedure together.

 

[SJones]

Firstly, get hold of the complete purchase documentation and the inspection documents (MTRs in American English) for the corroded casing and find out what the exact chemical composition, manufacturing process, and heat treatment condition was. You will note that the chemical composition requirements of API for K55 are not the most detailed in the world! Once you have fully characterised the original material, and worked out whether additional requirements like toughness testing and hardness control are required, you should be in a position to have a little mock up trial

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/