I suggest the use of a PMI to verify material chemistry before you get into attempting this repair. Good NDE companies will be able to help with this. The condition you describe should provide a much longer life than five years; I would be suspicious of the material. I would also do a baseline RT on any joint you will be repairing to make sure you have the complete scope understood before commencing the repair.

Once verified: Preheat to 300 deg F, weld with ER90S-B3 and E9018-B3 (some codes do not allow the use of low carbon filler if they will be subject to temperatures 850 F and above. Because of that rule, we do not allow the use of L designated filler.). If not possible to complete the weld in one shot, complete at least 3/8" of the weld before stopping. Raise temp to 400 to 600 degrees and hold for 2 - 3 hours. After that it may be allowed to slowly cool to ambient. Visually inspect the weld and re-establish preheat prior to completing the weld. Once completed, if PWHT will not begin immediately, do the heat up again (as described above). PWHT at 1350 +/- 25 deg F for two hours (in accordance with the rules of B31.1).

Unless there is a problem with the material, these steps should work fine.

Some other things to consider: is the correct pipe support system used (does it allow expansion & contraction), is this system thermally cycled excessively, is there some other restraint causing excessive stress? is water hammer a factor?

If this were my system I would do considerable research into the cause of these failures before I spent any money correcting them. Charles Hall

The major problem when welding these materials, is hydrogen cracking. Your description does however not sound like typical hydrogen cracking.

If this line was in service for 5 years before cracking, then these cracks would not be due to hydrogen cracking due to the welding. We therefore need to find a reasonable explanation for the in-service failures.

In my experience, the major reason for such cracking would be caustic cracking. If you also have one or more of the following, then it could be a sign of caustic cracking:

1)Cracking of the boiler feedwater pumps. (If these are not S/Steel.)
2)Cracking of de-superheaters.
3)Cracking of deaerator vessels.
4)Problems with water conditioning.

If the cracking is due to caustic, then the repairs will also be very difficult, typically resulting in additional cracking occurring.

The bottom line, is to find out why the cracking is occurring. A decent metallurgist should be able to perform a failure investigation and give you the answers you need.

Hope this helps

Niekie Jooste

Steamfitter,

I can appreciate your situation. It was improper of your employer to expect you to solve the problem in this situation. Cracking in steam lines is serious business that could get someone killed easily if the wrong conclusions are reached. There are many things that could lead to the problem you are being asked to fix, such as creep damage. It is very likely that either the wrong pipe or weld material has been used previously and when subjected to high steam temps, creep damage has occured. Something like 90% of the component life is used up initiating the crack when creep occurs and the remaining 10% of the time left is not much time to failure. The stresses are highest in the circumferential direction, so the cracks will tend to run transverse to the weld as you have seen. Grinding out the cracks and rewelding will not fix the problem if creep damage is occuring.

There is also a phenomenom known as carbon migration that occurs in alloy steel welds where a mismatch in composition exists. If low carbon weld metal was used and a stress-relief heat treatment performed, it would not be unusual for carbon to diffuse from the higher carbon base metal into the lower carbon weld and leave a decarbuerized zone in the base metal next to the weld fusion line. A similar event would occur if carbon steel weld metal were used instead of ER90S-B3/E9018-B3 because of the mismatch in Cr and Mo.

The cause of the cracks needs to be determined before it can be repaired. The repair may require replacement of the pipe. Failure will be a fishmouth type failure and catastrophic. Tell them you won't work on it till a thorough metallurgical evaluation is done. If they balk, call the chief boiler inspector for the state you are in. If you don't know who it is, go to http://www.nationalboard.org/members/mb_index.html and look it up. For New York go to http://www.nationalboard.org/members/ny-white.html You don't want to get caught in the middle of this one.

Marty