Weld imperfection

Date 01-13-2006 06:43

If the piping lines to be used for process,with welding defects as the owner,s decision due to some reasons,contrary to our recommendation(we are client,s consultants) with following conditions:
1- Specificatin type and grade of material:(A335 P11CL1,A691 1 1/4 Cr CL22) and P No.4.
2- The thickness :more than 13mm,require PWHT.
3- The service is high pressure steam(the pressure is more than 42 bar and the temprature is more than 370 centigrade).
4- The type of welding defects:LOF,LOP
Will you kindlly let us know:
1- How long will be the life expectancy of the A.M.welds?
2- If welding defects are repaired and radiography results are acceptable
before PWHT,is it possible to ignore the radiography after PWHT?
(although this is against the standard)
3- When the joints were repaired,PWHT was performed by contractor mistake,now is it necessary for the joints to be cut and rewelded and again PWHT performed?
Best Regards
O.khodabandeh

By George-kh (**)

Date 01-20-2006 03:44

1. It must be analyzed in a laboratory to know extend of life of your welds with their defects.
2. For Cr-Mo steels there is a risk of “reheat cracking” after PWHT and because of this reason code asks for RT after PWHT.
3. Sorry I didn’t understand your third question exactly. May you explain it more clearly?

By khodabandeh (**)

Date 01-20-2006 04:57

Dear Goerge,
My third question meaning is that if PWHT is performed on welded joints with defects does it require to cut the joints? because after removing the welding defects,PWHT is necessary, for this reason we will have twice and that will change the micro structure of material.

By George-kh (**)

Date 01-20-2006 05:45

Well, it seems that I’ve answered your third question in your question with “post weld heat treatment” topic, just before. However I repeat it again here:
According to ASME B31.3 paragraph 328.6 that is mentioned for repairing: “Preheating and heat treatment shall be as required for the original welding. See also paragraph 341.3.3.”
Therefore, after NDT, which is done after PWHT, if there is a repair, PWHT shall be repeated. You don’t need to cut out the joint. Just do another PWHT on it.

By khodabandeh (**)

Date 01-20-2006 06:11

Dear Goege,
Did not change micro structur of material with 2 time or more time PWHT?Did not change the strength of weld metal and heat affected zoon?

By George-kh (**)

Date 01-20-2006 22:02

Well, if your material was Q & T (Quenched & Tempered) material your answer was “Maybe”. Mechanical properties of Q & T materials come from their heat treating; either they are tools Q & T steels, or high strength Q & T structural steels. Many times PWHT or repairing may cause OVER TEMPERING of the material and softening it.
It is true for thermo-mechanical and fine grain steels because of risk of GRAIN GROTH in the material.
However, I said “Maybe” because it is difficult to say how many times PWHT or repairing effect the material seriously.
Your material is Cr-Mo steels which is creep resistant material. Cr is for resisting oxidation in high temperature and Mo is for creep resisting. Not special heat treating to improve mechanical properties, as I know, this group of steel needs; therefore two or some more PWHT do not effect their mechanical properties seriously, I believe. However, be careful about “reheat cracking” after PWHT.
On the other hand, code says nothing about this regard, so there should be nothing to be worry about it. What your specification says?

By khodabandeh (**)

Date 01-29-2006 06:03

Dear George-kh,
With all due respect to your good self,our specification does not mention anything.
Best Regards
O.Khodabandeh

By rodofgod (**)

Date 03-05-2006 00:00

Hi All!

if, as I read this right, you have two (2) repairs (and 2 PWHT) on the same weld, then you should cut out and start again!

Regards

By George-kh (**)

Date 03-09-2006 19:55

Hi Rodo,
Would you please explain your reason?