When to Use Seamless and Welded Pipe - Eng-Tips

LittleInch

Petroleum

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GB

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.

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SmallInfo

Petroleum

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PK

LittleInch,
Its H2S rich
b31.8
8" size
Client will ask why I am selecting seamless or welded.
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LittleInch

Petroleum

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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.

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TiCl4

Chemical

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CA

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.
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EdStainless

Materials

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Waukesha WI USA

Seamless will have much more variation in wall than welded.
Seamless also usually has a rougher ID surface.
In ERW steel pipe there can be selective HAZ corrosion attack because it isn't full body heat treated after welding.

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weldstan

Materials

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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. Upvote 0 Downvote

MJCronin

Mechanical

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Apr 9,

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US

My two cents ...
[ul]
[li]No piping code or standard will tell you when to use more expensive seamless piping and when not to[/li]
[/ul]
[ul]
[li] Are you selecting schedule 80 pipe for this corrosive service ? Having a thicker wall will make the piping last longer[/li]
[/ul]

[ul]
[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]

[/ul]


MJCronin
Sr. Process Engineer Upvote 0 Downvote

TiCl4

Chemical

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CA

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. Upvote 0 Downvote

SmallInfo

Petroleum

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Oct 30,

104

Location

PK

Littleinch, TiCI4, Edstainless, Weldstan, MJCronin
Thank you so much for your valuable time and information you shared, now its clear to me.
Thanks again you all Upvote 0 Downvote

EdStainless

Materials

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Waukesha WI USA

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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r

Mechanical

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AR

For 10-15 years choose the cheapest.

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Petroleum

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PT

Each great project company in oil industry have its own basic engineering specs based on standaed codes, I am afraid you won´t recieve the wright answer here.

REGARDS Upvote 0 Downvote

Daren Samy

Mechanical

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PK

Use seamless pipe. ERW pipe is not recommended in severe conditions. Welded point is weak points and it is at risk of failure

Daren! Upvote 0 Downvote

dik

Structural

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CA

... but informative, nonetheless.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik
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Petroleum

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PT

Seamless steel pipe is better than welded pipe. Seamless steel pipe is limited in larged diameters up to 24". Upvote 0 Downvote

r

Mechanical

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2,998

Location

AR

@
You are wrong.
See SA-106
1.1 This specifcation covers seamless carbon steel pipe
for high-temperature service (Note 1) in NPS 1/8 to NPS 48
[DN 6 to DN ] (Note 2) inclusive, with nominal (aver
age) wall thickness as given in ASME B36.10M

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Petroleum

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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. Upvote 0 Downvote

EdStainless

Materials

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May 20,

16,354

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Waukesha WI USA

Seamless pipe isn't better than welded, it just has different types of defects in it.
With welded you get very uniform surface finish inside and out along with very uniform wall thickness.
The type of welding will dictate the nature of weld imperfections that you should be testing for, and the HT method (local to weld or full body) will influence the final properties of the pipe.
Seamless pipe will always have very significant wall thickness variation (commonly over +/-10% in each length) and the ID surfaces can have significant variation in surface.
Tears and cracks on the ID surface are not uncommon in seamless product.
Seamless over ~24" OD is usually forged hollows made in short lengths.

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When you are first looking to source a stainless steel pipe, whether it’s for a desalination plant, an oil rig or even a nuclear power station, one of the first questions you need to ask yourself is ‘do I need a seamless, welded or forged pipe’? The three types all have different advantages and are therefore suited to different applications and environments. An abundance of factors should be taken into consideration when choosing what is right for a particular project.

Goto Nearyz Resources to know more.

Engineers will more than likely instinctively know the answer to that question, but let’s spend some time exploring these seamless, welded and forged pipes and their various properties.

Seamless Pipe

Let’s start with seamless pipe. As the name suggested, a seamless pipe is one without any seam or weld-joint.

Manufacturing and applications:

Seamless pipes can be manufactured using various different methods, which is very much dependent on the diameter required, or the ratio of the diameter to the thickness of the wall. In general, the manufacturing process of seamless pipe starts with raw steel being cast into a more workable format – a hot solid billet. This is then stretched out and pushed or pulled over a form. This hollow pipe then undergoes an extrusion process whereby it is forced through a die and mandrel. This works to increase the inside diameter and reduce the outside diameter.

Seamless steel pipe is regularly used in the transportation of fluids such as water, natural gas, waste and air. It is also regularly required in many high-pressure, high-corrosive environments such as in the oil & gas, power generation and pharmaceutical industries.

Advantages:

1. Strength: Seamless pipes come with the obvious advantage of having no seam and therefore no chance of a weak seam. This means that typically, seamless pipe can withstand 20% more working pressure than welded ones of the same material grade and size.
2. Resistance: The lack of seam means that seamless pipe can offer higher resistance to corrosion because there is less opportunity for things like impurities and defects that can more commonly occur along a weld.
3. Less Testing: It goes without saying that seamless pipes don’t require testing for weld integrity – no weld means no test!

Welded Pipe

Welded pipe comes in three forms: welded on the outside diameter, welded on the inside diameter or welded on both sides. The commonality is that they all have a seam!

Manufacturing and applications:

The manufacturing process of welded pipe starts by rolling out a steel coil to the desired thickness to form a flat strip or plate. This is then rolled, and the seam of the resultant tube is welded in a chemically neutral environment.

In regard to what type of steel is weldable, austenitic steels are generally the most weldable whereas ferritic steels are weldable in thin sections. Duplex steels are now regarded as fully weldable, but they do require more care than austenitic steels.

For more Straight Seam Welded Pipeinformation, please contact us. We will provide professional answers.

Welded pipe manufacturing techniques are thought to have greatly improved over the past few years. Arguably the most significant advancement being the development of using high-frequency electric currents as a welding technique. This has greatly improved the ability of welded pipe to avoid corrosion and seam failure.

While it is correct that the seam in a welded pipe makes it theoretically weaker, manufacturing methods and quality assurance procedures are far more superior these days. This means that as long as a welded pipe’s specified tolerances for temperature and pressure aren’t surpassed, there is no reason why is shouldn’t perform just as well as a seamless pipe in a wide array of industries.

Advantages:

1. Cost: A big advantage of welded pipe is that it is the least expensive of all pipe types and it is much more readily available.
2. Consistency: It is generally accepted that the wall thickness of welded pipes is much more consistent than that of seamless pipes. This is because the manufacturing process starts with a flat sheet of steel.
3. Surface quality: The avoidance of the extrusion process also means that the surface of a welded pipe can be much smoother than a seamless pipe as well.
4. Speed: Shorter procurement lead time is required for welded pipe due to the manufacturing process being simpler.

Forged Pipe

Forging steel is a metal forming process that shapes metal using compressive force and extreme heat and pressure.

Manufacturing and applications:

The manufacturing of a forged pipe starts with a piece of steel (whether that’s 6% Moly, Super Duplex, Duplex, Stainless Still, Nickel Alloy) being placed between an upper and lower die. Heat and pressure mould the steel into the desired shape and it is put through a machining process where it is finished to meet all of the required specifications.

This complex manufacturing process does result in higher cost implications for forged pipe.

The many advantages of forged pipe mean that it has a number of different applications in a diverse range of sectors such as oil, gas, hydraulic machinery, fertilisation and chemical. The fact that forged steel has no seam or welding point allows it to successfully contain potentially harmful or corrosive substances and their fumes. Therefore, it can be used in many heavy industries.

Advantages:

1. Strength: Forging pipe usually results in a strong and very reliable end-product because forging causes the grain flows of the steel to alter and align. In other words, the steel becomes more refined and the pipe’s structure is changed unequivocally resulting in sheer strength and high impact resistance.
2. Longevity: Forging excludes the potential for porosity, shrinkage, cavities and cold pour issues.
3. Economical: It is generally accepted that the process of forging is very economical as no material is wasted.
4. Flexibility: The steel forging process is very flexible and can produce many different pipes of varying sizes.

Sourcing seamless, welded or forged pipe from Special Piping Materials

Whatever variety of seamless, welded or forged pipe you require, rest assured that Special Piping Materials is able to source and supply all sizes of seamless pipe, welded pipe and forged pipe. Our vast global network will be able to find and stock whichever type you need, in whatever material grade – be it super duplex, duplex, nickel alloy, 6% Moly or stainless steel. The trusted mills that we work with are highly efficient and specialists in their respective fields, ensuring that your products are exactly how you need them.