steam supply (seamless or welded pipe) 2

[Prestz]

I know that the schedule and the fluid are important to determinate the kind of piping for an new installation.
For steam supply in a common power plant 150# or 300#, what is it as the suggested pipe to install?, of course without considerer economical reason. (the seamless pipe is more expensive than welded)
Thanks advance

 

[salmon2]

I am a big fan of welded pipes, even though a lot of people don't like welded pipe I think. Welded pipe can a decent choice. But really depending on if you have any specific concern.

But I also understand that people usually have a more peaceful mind when they know that the pipe is seamless instead of welded.

Regarding the economics, when the wall is very heavy, the welded pipe is not that cheaper than seamless any more.

I am not in power plant business, but specific concern or quetions can help others to respond.

 

[Mr168]

I just happen to have the line class spec for our next fossil job on my desk. Skimming through it, everything involving low to intermediate steam or water pressure calling for carbon steel uses A106 Grade B seamless pipe.

 

[davefitz]

check the b31.1 code to see if welded pipe is permitted- I don't have my copy handy , but I do not believe it is permitted for piping in the workspace. Safety is the issue- if the foundry's continuous UT machine was not performing properly, they could have shipped out a bunch of poorly welded pipe and if it fails in the workspace then a worker could get cooked.

Welded tubing within the boiler enclosure is permitted by code, but some customers will not allow it for issues related to reliability. One US boiler mfr had used welded carbon steel tubes in HRSG's built about 7 yrs ago, but because the foundry's UT machine was not performing properly , a lot of tubes failed which led to a massive set of lawsuits related to the lost unit availabilty and cost to replace all CS welded tubing.

 

[Joesteam]

Interesting this came up, article on sustainability in this months ASHRAE journal. One of the recommendations is to use seamless pipe. If they recommend for HVAC, why not power?

http://mag1.olivesoftware.com/am/welcome/AJL/ASHRAE-07-2008.asp

by the way, I thought this was a well written article...

Joe Lambert

http://www.control-associates.com/

 

[Mr168]

Another thing to note aside from the quality control of the welded seam, is the overall quality of the pipe. While not as much of an issue in small diameter pipe, the concentricity of larger diameter seamless pipe is far more consistent. Depending on how bad the ovality is of the welded pipe, you can have field construction issues with weldability for full penetration joints, which under B31.1 is just about everything. These mismatches from ovality are emphasized to an even greater extent if the company implements any orbital/automated weld procedures.

 

[metengr]

B31.1 permits seam welded pipe, up until recently, ASME Section I did not permit welded pipe. Of course, using weld pipe now requires weld strength reduction factors in the creep range (time dependent properties).

 

[JohnBreen]

Prestz,

Exactly as Metengr says. Look into the weld strength reduction factor and pay attention to B31.1, Paragraph 102.4.3 and Table 102.4.3 regarding longitudinal joint weld efficiency factors. For some P/T services the seam welded pipe might require additional wall thickness or additional NDE of the seam weld.

John

 

[Greg80]

According to ASME B31.1 you have to use seamless carbon steel pipe

 

[moltenmetal]

Proper design is of course key. The two are not interchangeable due to the joint efficiency.

In terms of ease of fabrication and quality, your mileage may vary depending on whose pipe you buy, what material and what size. I've seen lots of seamless pipe and tubing which was pretty horrible on the ID, whereas someone else here claimed that the ovality can be bad on welded pipe yet I've never personally seen the latter.

We've not seen an example in our shop yet, but have heard plenty of rumours on this forum and elsewhere that A53 welded pipe, particularly from China, sometimes has a seam of questionable virtue regardless what the mill certs say. Considering how cheap A106 seamless is at small sizes, it's one of the few occasions where I'd say that seamless is worth the premium even when not hard spec'd by a client or a Code.

 

[metengr]

According to ASME B31.1 you have to use seamless carbon steel pipe

Where? Appendix A mentions limitations for use for BEP (boiler external piping) only, and as I said because of Section I. For BOP, you can use seamless.

 

[metengr]

......seam welded OR seamless.

 

[davefitz]

Yes, Meteng is correct- it must be permitted to allow seam welded reheater piping- for large plants this can be in excess of 48" OD, and as such can only be provided as seam welded.