ERW and DSAW pipes 1

[jzhu35]

Does anybody here know whether there are differences for corrosion resistance of welds of ERW and DSAW pipes? per API 5L for same grades.

 

[metengr]

What is the environment and application?

 

[jzhu35]

Thanks for response. It is cooling water pipeline. Ambient temperature and low pressure. Our vendor want to use ERW pipes to substitute DSAW pipes. My concern is their corrosion resistance difference. If there is no much difference I think the substitution should be OK. How do you think?

 

[metengr]

There could be differences in corrosion, especially in a water (aqueous) environment. For ERW (electric resistance welded) pipe there is no filler metal that is added to make the weld. The two edges of the plate are roll formed and are sent thru copper dies that contain an electric current. The edges of the plate are locally heated from electric resistance and under pressure are fused to form the pipe or tube.

In comparison, double submerged arc welded pipe requires a filler metal.

Anytime filler metal is added you have a local region that is somewhat different in chemical composition to that of the surrounding base metal because the weld metal is an as-cast structure (like a casting). Depending on conditions, I could see where you might have corrosion of the either the DSAW or adjacent base metal, along the fusion line. In comparison, the ERW is formed from the same material and is considered homogenous in chemical composition with the base metal.


For water wetted conditions, I would stick with ERW.

 

[SJones]

The seam of the ERW pipe may or may not be heat treated thereby creating a different zone of microstructure. This difference in microstructure can also lead to corrosion. The simple thing is to ensure that the fluid is not corrosive which will probably lead to the next question!

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[gopalsankar]

We are using ERW pipes (below 12") in treated cooling water service the most the failures occured in the weld seam.Whereas no failure was reported in the DSAW/EFSW pipes.

 

[rconner]

It appears you have gotten some mixed response to your inquiry. If the water exposure conditions are aggressive in general to steel, it might be appropriate instead to consider utilizing a lined pipe system (that would perhaps make any arguable differences primarily academic?) -- e.g. cement mortar lined steel pipes per American Water Works Association ANSI/AWWA C205, AWWA STANDARD FOR CEMENT–MORTAR PROTECTIVE LINING AND COATING FOR STEEL WATER PIPE—4 IN. (100 mm)AND LARGER—SHOP APPLIED (or field lined per AWWA C602), or standard cement mortar lined ductile iron pipe per AWWA C151 and AWWA C104 etc.

 

[metengr]

gopalsankar;
Was the ERW pipe subjected to a normalization heat treatment to remove the base metal HAZ? If this was done for ERW pipe, there should be NO corrosion. The normalization heat treatment may have been done for the double SAW pipe.

 

[jzhu35]

Thanks for all response.

I did some study and I found that both ERW and DSAW pipe have been involved in SCC-related failures. There is no obvious unique metallurgical characteristics associated with the failures.

For the time being, I won't consider their corrosion resistance difference anymore.

 

[stanweld]

gopalsankar,
Depending on the manufacturer of the ERW pipe, you may find increased leak sources in its weld seam due to increased number of flaws in the weld seam relative to that found in DSAW pipe. Flaws open to the surface provide a profile which may be susceptible to accelerated corrosion.

With regard to heat treated condition of EFW pipe, I performed testing whereby the weld seam was locally induction normalized, locally induction tempered, full body normalized and full body tempered. Only the full body normalized pipe had a homogenous microstructure. If there were no inclusions to verify the upset during welding, one could not locate the weld seam in the full body nornmalized ERW pipe.