weldability of API 5L X70 to A106 Gr B 4

[Mous1747]

i was wondering what are the weldability constraints or limitations or if it's even acceptable to weld two pipes with large mismatch in SMYS, will that be a cause or induce any issues? i appreciate all the answers in advance

 

[metengr]

Yes you can weld them with conventional welding processes. The filler metal strength can either be matched to the higher strength or lower strength base metal or in between the strength levels. The strength of the weld joint should be evaluated to ensure adequate design margin for expected loads in service.

 

[Mous1747]

thanks for looking into this, what are the codes that specify the methods you stated above?
for example i know that B31.8 I-1.1(c) states to match the material with higher SMYS, and B31.4 as well.
i searched BPVC IX and API 1104 but didn't find anything

we normally match the material with higher SMYS until i recently heard about 1:1.5 limits on SMYS inequality to eliminate stress riser. i am not sure where that came from but i strongly doubt the validity of it.

 

[metengr]

The Codes do not specify a particular strength filler metal for use, that is left up to the engineer of record and acceptable qualification of a WPS under Section IX.

 

[weldstan]

What's the required Code? If it's B31.3, metengr has provided the answers.

 

[Mous1747]

the design is per B31.8 but it will be field weld as per API 1104, i am not sure which one of the 2 codes will be followed and whether they have conflicting info. i heard if API 1104 is used, the whole B31 is thrown out of the window

the customer pipeline is API 5L X70 , and the sleeve is A106 Gr B, the customer is asking me whether this large SMYS mismatch will induce any stress riser, the problem he is asking me for proof whether from code or design?

 

[gtaw]

I doubt there will be any problems from a metallurgical standpoint. While the chemistry will differ slightly, that is not uncommon. Rarely does the filler metal chemically match the base metal.

The could be a design issue if the designer doesn't consider all the issues related to design such as fatigue if there is thermal cycling, bending, the effects of stress risers, proper reinforcement, etc.

API basically addresses how the WPS and welder qualified and testing and acceptance criteria for the welding. It is not a design standard, that's where B31.8 comes into play.

Best regards - Al

 

[weldstan]

Then B31.8 governs the filler metal(s) to be used.

 

[Mous1747]

Great. Thank you so much all for all the valuable info.

 

[SectionIX]

You will need to make sure the WPS you use was qualified on API 5L-X70 material per API 1104, 5.4.2.2: "When welding materials of two separate material groups, the
procedure for the higher strength group shall be used".. Same for the repair WPS if you qualify them separately.

If you do this routinely, you may want to develop an API 5L-X70 to API 5L Grade B WPS qualified with additional testing (impact [at the design temperature] and hardness) not required by the 49CFR Part 192.7 referenced edition of API 1104 (20th). This due diligence will demonstrate the ability to make sound welds to both yourself and the regulator. Be aware, however, this specific combination (API 5L-X70 to API 5L Grade B ) will only apply to the combination API 5L-X70 to API 5L Grade B materials.