In service welding 1

[Dario2002]

What are practical experiences with in service welding on high pressure gas pipeline (pressure containing metal sleeve)?

Assuming that welding procedure is verified, preheat is controlled (up to 100°C), surrounding temperature is quite low (around -5°C), natural gas is flowing through 20" pipe (GrX52, 7mm) at around 2-3 m/s, welding is inspected by ultrasound (B scan) and magnetoflux, is there any issues to be expected?

Is environment temperature of -5°C big influence in HAZ (heat affected zones), due to faster cooling, in comparison with possible spring/summer temperature of 20°C?

 

[BigInch]

Ask your hot tap contractor, or TDW, about that.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Dario2002]

That's the point of my post. I want second opinion or experience.

Contractor is experienced (in few occasions they also subcontracted for TDW for hot tapping), and they sad that normal conditions are usually is around 20°C, but with preheating they do not expect additional problems. I just need some confirmation for that.

 

[BigInch]

I don't think it is an unreasonable expectation. You do expect to have a welding tent on hand, right?

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[austsa]

Typically, weld cap hardness is the issue for in-service welds. No problems if you have a good robust weld procedure and skilled welder.

 

[anglisk]

Hi Dario,

Depending on the weld procedure, you have to be careful that it is qualified properly. Codes in Canada that include in-service welding requriements include CSA Z662 for pipelines and API 2201, API 577 Section 11 and ASME PCC-2 for plants. However, weld procedures in the States reference in-service welding requirements from API 1104 Appendix B or ASME PCC-2 (and others). It is also important that the qualification of the welder is completed properly. Also, if the procedure you are reviewing uses 6010 root, expect a failure within 5 years.

Given the above, with regards to preheats, procedures that are qualified using an overlapping and/or tempering technique typically only require 50 degree F (10 degree C) preheat, unless the line is sour. If the procedure you are reviewing requires a preheat of 212 degrees F (100 degree C), it will be next to impossible to achieve this preheat without the use of thermal couples in the field (which has been done, but requires engineering judgement based on flow, product etc.).

Furthermore, in-service welding procedures typically require a measurement of cooling rate during qualification and in the field, such as the Edison Welding Institute method. If this isn't on the procedure, I would recommend another contractor such as TDW (who has been hot tapping for at least 40 years).