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When to Use api 5l seamless pipe?

Author: Monica

Aug. 25, 2025

1 0 0

Tags: Agricultural

When to Use Seamless and Welded Pipe - Eng-Tips

LittleInch

Petroleum
Joined
Mar 27,
23,229
Location
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.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it. Upvote 0 Downvote

SmallInfo

Petroleum
Joined
Oct 30,
104
Location
PK
LittleInch,
Its H2S rich
b31.8
8" size
Client will ask why I am selecting seamless or welded.
Thanks for reply Upvote 0 Downvote

LittleInch

Petroleum
Joined
Mar 27,
23,229
Location
GB
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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Also: If you get a response it's polite to respond to it. Upvote 0 Downvote

TiCl4

Chemical
Joined
May 1,
646
Location
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
Joined
May 20,
16,417
Location
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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P.E. Metallurgy, consulting work welcomed Upvote 0 Downvote

weldstan

Materials
Joined
Jun 24,
2,818
Location
US
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
Joined
Apr 9,
5,102
Location
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
Joined
May 1,
646
Location
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
Joined
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
Joined
May 20,
16,417
Location
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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P.E. Metallurgy, consulting work welcomed Upvote 0 Downvote

r

Mechanical
Joined
Jan 12,
3,065
Location
AR
For 10-15 years choose the cheapest.

Regards Upvote 0 Downvote

Petroleum
Joined
Jun 25,
3,468
Location
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
Joined
Oct 6,
59
Location
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
Joined
Apr 13,
26,157
Location
CA

... but informative, nonetheless.

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

-Dik
Upvote 0 Downvote

Petroleum
Joined
Jun 25,
3,468
Location
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
Joined
Jan 12,
3,065
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

Regards Upvote 0 Downvote

Petroleum
Joined
Jun 25,
3,468
Location
PT
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
Joined
May 20,
16,417
Location
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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P.E. Metallurgy, consulting work welcomed Upvote 0 Downvote

Role of API 5L Gr B Seamless Pipe in Marine Industries - Amco Metals

Marine industries significantly connect different parts of the world by transporting goods and people over long distances. Hence, reliable and cost-effective transportation is a necessity to ensure global connectivity. One of the most critical components ensuring marine transportation’s reliability is robust pipe systems. API 5L Gr B seamless pipe is one of the most popular seamless pipes used in the marine industry. In this blog post, we will explore the significant role of API 5L Gr B seamless pipe in marine industries.

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What is API 5L Gr B Seamless Pipes?

API 5L Gr B Seamless Pipes are high-quality carbon steel pipes that transport liquids and gases in various industries such as oil & gas, petrochemical, automotive, and power generation. These pipes are made from seamless steel machined to exacting standards to provide superior performance. The API 5L, Grade B specification, is the foundation for all pipeline products that use this pipe grade. One major benefit is its welded construction which eliminates the need for welding during installation or operation. Additionally, these pipes have a higher yield strength than standard grades of line pipe, which increases their long-term durability even under extreme pressure or temperature conditions. Furthermore, it features excellent corrosion resistance properties due to their special composition and advanced surface treatments making them perfect for applications requiring exceptional reliability without sacrificing quality or safety requirements.

Role of API 5L Gr B Seamless Pipe in Marine Industries

High Strength and Durability

API 5L Gr B seamless pipe is manufactured by using high-quality carbon steel. This makes it immensely strong, durable, and resistant to wear and tear. It can withstand high stress, temperature, and pressure, which makes it perfect for use in marine industries. This high strength and durability ensure that the pipes won’t break down and cause any interruption in the transportation of goods and people, making marine transportation dependable, reliable, and safe. API 5L Gr B Seamless Pipes are known for their high strength and durability. They are made from a combination of carbon and manganese, which gives them greater ductility and resistance to corrosion, even at higher temperatures. The seamless construction allows for improved flow characteristics. These pipes are an excellent choice for oil, gas, chemical, water distribution, or any other application where long-term strength is needed. The uniform wall thickness throughout the pipe also provides enhanced structural performance over welded pipes with variable wall thicknesses. Overall, API 5L Gr B Seamless Pipes provide superior cost efficiency and longevity compared to other materials used for similar applications.

Corrosion Resistance

Marine transport exposes pipes to harsh marine environments, including saltwater, humidity, and acidic gases. The exposure of the pipes to these environments can cause corrosion, leading to leaks and breakdown of the pipework system. API 5L Gr B seamless pipe is designed to withstand these harsh environments, which makes it corrosion-resistant, durable, and reliable. This corrosion-resistant quality of the pipe ensures the continuous flow of goods and people in marine transport.

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Marine transport is a time-sensitive industry; downtime can lead to significant losses. Poor-quality pipes can cause frequent breakdowns, leading to unexpected downtime, costly repairs, and loss of revenue. However, API 5L Gr B seamless pipe can last long with minimal maintenance, reducing maintenance costs. Hence, using API 5L Gr B seamless pipe minimizes marine transport’s downtime, making it a reliable and cost-effective option.

Easy to Install

API 5L Gr B seamless pipe’s seamless nature makes it easy to install, saving time and labour costs. The seamless nature of the pipe ensures no leak points or weak spots, making it an excellent choice for marine industries, where speed and accuracy of installation are critical. The ease of installation ensures the pipes are installed correctly, reducing downtime and lowering costs.

Eco-Friendly

API 5L Gr B seamless pipes are eco-friendly and sustainable. The carbon content of the pipes is low, meaning that they are less polluting and have a reduced carbon footprint. Additionally, the pipes are 100% recyclable, ensuring that they are reused and not thrown into landfills, reducing waste and preserving the environment.

Conclusion

API 5L Gr B seamless pipe plays a crucial role in marine industries by providing strength, durability, corrosion resistance, reduced maintenance costs, ease of installation, and eco-friendliness. The pipe ensures that marine transportation is reliable, safe, and cost-effective, making it a popular choice in the industry. Therefore, using API 5L Gr B seamless pipe is essential for the success of the marine industry.

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