Waiver of PWHT with CTOD's

[nickt1960]

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?

 

[GRoberts]

For only 3 or 4 welds it seems like it would be a lot easier to switch to a FCAW wire with better PWHT impace properties, or even switch to a SMAW electrode, than conduct CTOD tests, which can be problematic, not to mention expensive and not very timely.

 

[sayee1]

To answer to your question NickT, even if anyone had the data for CTOD using FCAW GS, because no client is going to accept the data, reasons being, the consumable brand, the parameters used, base material properties etc are all going to be considered essentialo variables and without anything specified in specifications(I presume that is the case) you are going to find it difficult to reason with client. I agree with GRoberts that going for a consumable with better properties after PWHT would be a better choice.

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[stanweld]

Is only the weld metal affected? Or is the base metal and HAZ affected as well? If the weld metal is the problem, change the filler metal and/or welding process to accomodate the requirements.

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.

 

[JRWelding]

Hi Everybody,

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

 

[nickt1960]

We need to meet -29C requirements as this is the topsides riser pipe that flows into the pig launcher, not the main pipeline which is rated at 0 celcius. Nevertheless the problem was in the weld metal not HAZ or parent metal so the pipe is not the issue.

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?

 

[GRoberts]

Personally, I would stay away from the Cr-Mo consumables as they are not known to get very good toughness even though they will resist softening during PWHT if that is you concern. You might consider, depening on your exact strenght requirements, 8018-C3, 9018M, 10018M, or 10018-D2. Those would be the first ones I looked at anyway.

 

[stanweld]

Absolutely stay away from the E8018-B2 electrode. E8018-C3 has been used extensively in Arctic and North Sea Service with and without PWHT.

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.

 

[GRoberts]

I believe that stanweld is correct that there are FCAW wires that would meet your requirements. However, the basic wires do not run that well out of position and are not as easy to use (smoke, spatter, slag detachment). In the case of your low number of joints, I would stick with SMAW as it has a higher likelyhood of sucess the first time, and the productivity gains that would be made with FCAW would not be that substantial.

 

[nickt1960]

Thanks for the advise on the 8018-B2, I will try to find an 8018-C3, Lincoln don't seem to have one in the catalogue that I have.

 

[sayee1]

Lincoln has 8018C3, manufactured both in the US of A as well as Netherlands. Ask for LH8018C3 MR or Kryo 1(I do beleive these are the brand names for 8018C3 if my memory serves me right)

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
End of all knowledge is the attainment of immortality!

 

[nickt1960]

Yes, now that I've looked again, I've found it in the Lincoln weldirectory. I am in fact going to try 8018-C1 which has better impact properties after PWHT (at lower temps).


Thanks to all.