When is welded pipe not acceptable? 2

[jmkates]

Hi All,
This is my first post on the site, so I hope to honor the code here. I have searched for answers online, but they are fairly general.

My curiosity lies around welded vs seamless pipe considerations where corrosion is severe. I'm hoping to learn if there are design codes or standards that dictate which to choose, or if these are mostly design preferences. I am also hoping to learn if there are any applications where welded is just not allowed.

Help me understand?

 

[ShabsRBI]

Under severe corrosive conditions Seamless piping is used. Seamless piping is also a preferred option under High Pressure, high temperature, cyclic services. ASME code B31.3 does not specifically provides a guideline to select between Seamless and ERW piping but considering the joint efficiency of Seamless pipe ( E=1) and ERW ( E=0.85) the required thickness of ERW piping is generally 15-20% higher than the Seamless piping for given pressure and temperature.

In Petrochemical, power generation and Oil and gas industry seamless piping is used for all critical services. Only non critical services like Cooling water, air or large diameter flare systems, welded pipes are used.

 

[LittleInch]

Shabs, I think, you may be referring only to specific plants and fluids. Because B31.3 doesn't like welded pipe, people tend to avoid it, but other design codes don't have this issue and certainly pipeline codes which transport many corrosive substances allow them without impact on wall thickness.

There are issues with welded carbon steel pipe in terms of Hydrogen embrittlement and H2S service where seamless can be preferred, but if the material is acceptable from a corrosion point of view,then it can be welded pipe.

This is normally something for which materials engineers advise.....

Company guidelines or specifications may have guidance, but design codes tend to leave decisions like this to designers who have all the information available to them, unlike the code writers who can't cover all the possible permutations of fluids, pressure, temperature, design life, risk levels, material properties etc etc

 

[SJones]

This also opens the discussion up to the allowance, or prohibition, of different types of welded seam. Most of the discussion will be urban legend with some “code requirements” and personal experience thrown in. The question is too generic to start a deeper dive. How about narrowing it down to a particular industry for starters.

 

[r6155]

Seamless pipe for Lethal service and Nuclear.

 

[jmkates]

Thank you all for these helpful answers. What would you say is the best way to learn about critical services? Through the materials engineers?
In my head an industrial plant is really large and has many processes, but it would seem that critical service is going to be a much smaller part of the process, is that accurate?

 

[LittleInch]

Depends how it is defined or interpreted.

Lethal service is defined as such in ASME B 31.3

"Critical" is in the eye of the process engineer / operations staff. Critical to what? The operation of the plant or a big disaster if it fails and blows up / kills people?

A large diameter low pressure water line could be critical if it carries cooling water and if it breaks all the plant stops working...

 

[EdStainless]

Depends on the material and service.
First here is very little in Codes or Standards related to corrosion resistance.
This is the responsibility of the end user.
For materials/specs where the pipe is annealed after welding (such as in most SS) there is no performance difference between seamless and welded.
It comes down to preference of the owner, which specs/standards they want to use, product availability and price.
Usually, the NDT is far more important than how the pipe was made.
Often seamless has little to no NDT (maybe hydro only).
Compared to a welded product with ET or UT the seamless will often be inferior.
Lack of a weld does not assure lack of imperfections.
I only know of two applications where I would never use welded products.
The first is in creep limited situations and the second is HF service.

 

[jmkates]

Depends how it is defined or interpreted.

Lethal service is defined as such in ASME B 31.3

"Critical" is in the eye of the process engineer / operations staff. Critical to what? The operation of the plant or a big disaster if it fails and blows up / kills people?

A large diameter low pressure water line could be critical if it carries cooling water and if it breaks all the plant stops working...

I appreciate that 'critical' is subjective. Thank you for reframing that for me.

 

[jmkates]

Depends on the material and service.
First here is very little in Codes or Standards related to corrosion resistance.
This is the responsibility of the end user.
For materials/specs where the pipe is annealed after welding (such as in most SS) there is no performance difference between seamless and welded.
It comes down to preference of the owner, which specs/standards they want to use, product availability and price.
Usually, the NDT is far more important than how the pipe was made.
Often seamless has little to no NDT (maybe hydro only).
Compared to a welded product with ET or UT the seamless will often be inferior.
Lack of a weld does not assure lack of imperfections.
I only know of two applications where I would never use welded products.
The first is in creep limited situations and the second is HF service.

Very helpful! This gives me a very good start. Thank you all.

 

[TugboatEng]

If using carbon steel pipe in corrosive service the weld seam is anodic to the rest of the pipe. This will result in rapid failure without galvanic protection. Ed brought up a point that I was unaware of. If the pipe is annealed that there may be less of a different in galvanic potential. I have very mixed experiences with welded vs seamless stainless steel pipe. Even in the same system I'll see minimal effect of welded pipe with broadly distributed pitting on the seamless. The difference in annealing is a potential explanation of the experience.

 

[r6155]

Also, seamless pipe for hygienic service (food, pharmaceutic).

 

[LittleInch]

There are also differences between the types of welded pipe, whether its SAW or ERW.

Corrosion can do strange things to welds and HAZs which can't always be predicted. I've seen weld metal eaten away from its parent pipe as though the weld bevel had just been done. Other times it doesn't get as corroded as the main pipe. Go figure.

 

[jmkates]

There are also differences between the types of welded pipe, whether its SAW or ERW.

Corrosion can do strange things to welds and HAZs which can't always be predicted. I've seen weld metal eaten away from its parent pipe as though the weld bevel had just been done. Other times it doesn't get as corroded as the main pipe. Go figure.

Your comments (and others) reveal that there seem to be plenty of experiences that have provided on-the-job training. Where can I look inside an organization to learn more about these experiences?

 

[LittleInch]

Generally it's the grey / white haired guy in the corner of the office.....

Some bigger companies have formal and informal networks to get this personal in built experience into the heads of those who haven't been there and done it. Sometimes you can access that through organisations and associations / conference papers etc, but is a lot harder.