When to Use welded steel pipe？

Hi Experts,
I have to choose pipe welded or seamless for raw gas but it's for 10 to 15 years not more than that, its API 5L X42 fluid is corrosive, no high temperature and pressure. I am looking for any reference from any standard which tells when to use welded and seamless or at least some valid technical points to defend my selection.
Thanks in advance.

What design code?

How corrosive?
With what?
Size and wt affect availability. Above about 16 to 20" seamless gets hard to find

This is more of a material selection issue and I don't know if any pipeline code which will tell you this. B31.3 doesn't like welded pipe for some reason and applies a factor on wall thickness

There is a lot of preferential engineering here and different companies have different views.

There should be little difference but you may need to look at the impact of the seam weld on corrosion issues.

If you have sour service (H2S) then seamless is definitely preferred, which is a material selection issue under the NACE standards.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it. You need to ask a materials engineer, but I'm pretty sure for sour service you need seamless if possible and 8" the cost is about the same.

It's all about the hardness of the weld. Also look in your sour service specification.

Design wise in 31.8 it makes no difference and they won't guide you as it is not something B31.8 does.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it. A general rule for corrosive services is that seamless piping is preferred - ERW pipe tends to be attacked along the pipe-weld bondline at a higher corrosion rate than the base material. My impression (not fact!) is that mill tolerances for wall thickness are either higher for seamless pipe over ERW pipe or that they are harder to get within tolerance (more expensive). So if you need to do branch reinforcement calculations for larger diameters or higher T&P, the mill tolerance becomes important.

Piping codes don't generally tell you what pipe to use in a given application; there are generally too many factors and special cases, so they leave the application up to the user.
For your application choose seamless due to answers provided above. Due to our global supply chain and the vast differences in ERW welding methods from mill to mill and quality thereof, a greater chance of failure is incurred using ERW. ERW pipe can be made with excellent properties but you really have to know the mill's capabilities. My two cents ...
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[li]No piping code or standard will tell you when to use more expensive seamless piping and when not to[/li]
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[li] Are you selecting schedule 80 pipe for this corrosive service ? Having a thicker wall will make the piping last longer[/li]
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[li]Some B31 series piping codes have a higher allowable stress for seamless piping ..Seamless pipe can withstand 10-20% more working pressure than welded ones of the same material grade and size.. On what basis was your pipe wall thickness calculated ?[/li]

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MJCronin
Sr. Process Engineer MJCronin,

When would the MAWP of the piping become the deciding factor for a piping system's thickness at low temperature and pressure? In my mind, required thickness is often very low at low T&P, and other factors like maximum unsupported span and extra thickness for corrosion allowance tend to dominate. Typically pressure is also limited by the flanges or connectors rather than piping, is it not?

I'm not challenging you here, but rather curious as to where you've seen or heard of the extra MAWP of the seamless pipe being important in the selection of ERW vs seamless. At thicker walls the seamless premium is not very much more expensive.
Many ASME codes do derate welded tube by 15% for no reason other than it was welded.
The seamless tube will always be heavier and the thinnest spot will be thinner than with welded tube.
The greater wall variation is just a fact of life.


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P.E. Metallurgy, consulting work welcomed r
you're right, I was speaking generally. But the use of welded pipe and seamless pipe depends on the intended service. If it is going to be used for a lethal dangerous, high pressure or corrosive service I would use seamless pipe, if it is going to be used in an enoquo service I would use the cheapest welded pipe.