Welded VS. Seamless Steel Pipes: 5 Key Differences

What are the differences between welded VS. seamless steel pipes?

1. Applications
2. Manufacturing
3. Pros
4. Cons
5. Cost

As industrial and construction applications continue to develop, so do the materials they use. Piping products and systems that are crucial in these applications have evolved and grown more complex, resulting in a variety of pipe manufacturing methods. 

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Of all the types of pipes that exist, the most common and widely used products are welded and seamless steel pipes. Often, people wonder which is better for their application — which is why in this post, we discuss the differences between welded vs seamless steel pipes, and how to choose the best option.

Applications

Pipes are widely used in several industries today because they are highly functional and cost-effective products. They can be manufactured in different lengths and shapes, which allows them to be used in a variety of applications. 

For welded steel pipes, the misconception is that they are much weaker as weld seams are perceived as a structural flaw. While it’s true that welds are a strength concern, welded pipes go through several quality assurance regimens to ensure that the welded pipe will perform as desired when its tolerances aren’t exceeded. 

As a result, welded pipes are recommended for many different industries. Some of them are: 

• Food and beverage manufacturing
• Pharmaceutical manufacturing
• Automotive industry
• Construction and mining industry
• Architectural design
• Pipelines

Seamless steel pipes offer unique mechanical properties — such as non-welded joints, uniform strength distribution, and increased pressure capacity — that allow them to perform reliably. They may be able to withstand more pressure, higher temperatures, and heavier weights than welded pipes.

As a result, seamless steel pipes are recommended in situations where environments may be more demanding, such as:

• Chemical processing
• Medical equipment manufacturing
• Oil and gas lines
• Hydraulic systems
• High temperature and pressure systems
• Nuclear power plants
• Water purification plants

Manufacturing

Welded steel pipes start as steel plates and steel strips, called skelp. These pieces are bent and formed using a bending machine and rollers. When it reaches the proper thickness gauge, it is cut to the desired length and formed into a flat rectangular sheet. The width of the sheet’s shorter ends is the pipe’s outside circumference. This measurement is then used to estimate the pipe’s eventual outside diameter.                                                                     

The pipe pieces are then welded together — sometimes using filler material. Most welded steel pipes are also put through a heat-treatment process. Depending on the application, the pipe may be welded using automated methods, or through human labor. The method used determines the quality of the weld and the welded pipe as a whole.

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Seamless steel pipes start as a round piece of steel called a billet. The billet is heated until pliant, then stretched, rolled, and pushed using a frame until the billet forms a hollow shape. Another method for making seamless steel pipes is by pushing the billet through a perforated tube.

From there, a seamless steel pipe may be formed using hot-rolling, cold-rolling, or cold-drawn processes. A hot-rolled seamless pipe goes from forging the billet, to perforating, to rolling, to shaping. This method is used to make thick and large diameter seamless pipes. Cold-drawn seamless pipes are used to create products that are smaller in diameter or have thinner walls. It may also be used to create pipes with smoother internal surfaces.

Pros

There are many advantages to using a welded steel pipe for your application, such as:

• Can be made in longer lengths — no sizing restrictions.
• Manufacturing is cost- and time-efficient.
• Generally has smoother surfaces.
• Products are easier to make, so they’re readily available.
• Shorter delivery time
• Has thinner and more consistent wall thickness.
• Is lighter in weight.
• Possesses tighter tolerances.

Likewise, seamless steel pipes offer their own unique advantages that may put them above welded pipes, depending on the application. These advantages are:

• Has thicker walls.
• Has heavier weight.
• Needs no welding. Thus, no additional metals or materials are needed.
• No tests are required for weld integrity
• Improved corrosion resistance and durability.
• Improved “ovality” — a.k.a. “Roundness,”
• Can withstand more pressure.

Cons

As with every metal product, welded steel pipes have their fair share of disadvantages, which are: 

• Welds are more prone to corrosion.
• Must be tested extensively before use.
• Reduced ovality due to welding and manufacturing processes.
• Can’t withstand heavier weights or pressure.

Seamless steel pipes also have a few disadvantages that may make them unsuitable for your application, like:

• Restricted lengths and sizes due to manufacturing difficulties — nominal size is 24 inches or less.
• Manufacturing is costly.
• Seamless pipes may be more difficult to procure.
• The extrusion process creates a rough surface.
• Inconsistent wall thickness.

Cost

The cost of steel pipes heavily relies on raw material availability, the amount of labor needed for production, and the complexity of the manufacturing process. The mechanical properties of steel pipes also influence the product price. Altogether, seamless steel pipes are more expensive than welded steel pipes due to their improved strength, scarcity of raw materials, and labor-intensive manufacturing process. 

However, pricing may also vary throughout the year due to market pressure. There will be times when welded pipes will go up in price and become more expensive than seamless pipes. In these cases, it may be appropriate to purchase seamless steel pipe in the same dimensions instead, if budget is a concern.

Key Takeaway

Now that we’ve evaluated welded vs seamless steel pipes, you may have enough information on their key differences to choose the right pipe for your application. If you have questions, message Supreme Pipe today. We are the leading manufacturer and supplier of steel pipes in the Philippines, and we can help you pick out the best products for your project.

If you want to learn more, please visit our website Longitudinal Welded Pipe.

LittleInch

Petroleum

Joined

Mar 27,

23,178

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,

23,178

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.

Remember - More details = better answers
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.
Upvote 0 Downvote

EdStainless

Materials

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May 20,

16,411

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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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P.E. Metallurgy, consulting work welcomed Upvote 0 Downvote

weldstan

Materials

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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,

16,411

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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r

Mechanical

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AR

For 10-15 years choose the cheapest.

Regards Upvote 0 Downvote

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

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

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26,156

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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
Upvote 0 Downvote

Petroleum

Joined

Jun 25,

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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

Joined

Jan 12,

3,057

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,

3,465

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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,

16,411

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