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.

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.

If you want to learn more, please visit our website Xin Jiyuan.

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.

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.

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.

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.

For more information, please visit Welded Steel Pipes.