Waiver of PWHT with CTOD's
Waiver of PWHT with CTOD's
(OP)
We are needing to weld three to four topsides riser joints from X-65 line pipe, using FCAW-GS process (tig root). FCAW-GS consumable is lincoln 81-K2-H. Pipe size is DN700 x 39 mm wall thickness. Code is B31.8 which generally refers you back to API 1104.
At this thickness we need to PWHT. We are finding that the PWHT is degrading impact properties at the required -29 C and can't qualify the procedure. I am wanting to waiver the PWHT under clause A825 of B31.8 which permits this if we can demostrate that residual stresses are OK in the as welded condition. I believe CTOD's will justify such a waiver. However the A$20,000 this will cost us to run and test in australia does not make it cost effective for 3 or 4 welds. I am looking for a precedent or tech paper that has shown adequate as-welded properties for FCAW-GS on X65 line pipe in the past. Can anyone assist?
At this thickness we need to PWHT. We are finding that the PWHT is degrading impact properties at the required -29 C and can't qualify the procedure. I am wanting to waiver the PWHT under clause A825 of B31.8 which permits this if we can demostrate that residual stresses are OK in the as welded condition. I believe CTOD's will justify such a waiver. However the A$20,000 this will cost us to run and test in australia does not make it cost effective for 3 or 4 welds. I am looking for a precedent or tech paper that has shown adequate as-welded properties for FCAW-GS on X65 line pipe in the past. Can anyone assist?





RE: Waiver of PWHT with CTOD's
RE: Waiver of PWHT with CTOD's
Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!
RE: Waiver of PWHT with CTOD's
Microalloying elements, especially V and Nb and B can adversely affect the base material and HAZ toughness after stress relief due to secondary carbide/carbonitride formations at the stress relieving temperature. If this is the case, additional preheating and PWHT controls will be required to achieve the desired toughness. It may be impossible to achieve the required toughness with PWHT depending on the X-65 chemistry.
RE: Waiver of PWHT with CTOD's
I do not know what temperatures you use for PWHT but usually this is just stress relieving on temperatures around 600 and something deg. C. At this temperature in general nothing major happens to the microstructure of the steel and so I cannot imagine that the PWHT is your problem.
As stanweld already pointed out, it would be interesting to know in which part of the fusion zone you have this toughness problem and what are the minimum values to be achieved.
I think there is some other point to be considered, which is the test temperature. As per API 5L X65 line pipe shall be impact tested at 0 deg. C and should have a minimum average value of 27 J.
Lets say in "standard condition" or "out of the shelf" X65 is not really intended to be used in such low temperature applications and hence is not impact tested at such low temperatures. Therefore you may face problems to reach the Charpy values at minus 29 deg. C, especially after welding, which usually reduces the toughness in the HAZ even a bit further.
In pipeline projects, if there is such an requirement for "low temperature service of X65, you go to the steel manufacturer before ordering your pipe and they take care of that by alloying the steel in the right way or by applying different kind of heat treatment (QT) which will than give you the right Charpy values even at low temperatures.
Ok, since I do not know all your requirements I can't go further in the subject. Minus 29 deg. C is usually the temperature at which the filler materials are tested (weld metal only) but for a normal X65 (without any special precausions) it appears too much.
If you could submit further details we may have an other look on the problem.
Best regards
Joerg
RE: Waiver of PWHT with CTOD's
We are now conceding that flux cored consumables are too unreliable after stress relieving due mainly to microallying problems which causes a type of embrittlement. We are now switching over to SMAW followed by stress reliving (PWHT) at 600 C. I am trying to select a suitable electrode and am looking at a Lincoln E8018-B2 (brand SL19G). This is a Cr-Mo based consumable. Can anyone see a problem with compatability with X65 parent metal?
RE: Waiver of PWHT with CTOD's
RE: Waiver of PWHT with CTOD's
There are also some FCAW electrodes used with 75%AR min.-25%CO2max. that can meet your requirements with PWHT. They have been formulated to add more basicity in the fluxing agents and thus greatly reduce oxygen content.
RE: Waiver of PWHT with CTOD's
RE: Waiver of PWHT with CTOD's
RE: Waiver of PWHT with CTOD's
Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!
RE: Waiver of PWHT with CTOD's
Thanks to all.