Seamless pipe VS seamed (welded) pipe

The difference between seamless pipe & seamed (welded) pipe

Types of seamless pipe & seamed (welded) pipe

Seamless vs welded steel pipe differences summary

API 5L / ASTM Seamless steel pipe and ERW welded steel pipe have some differences as below:

1）Apperance differences

Seamless steel pipe used steel billet as raw material. The outer surface defects of billet cannot be eliminated by hot rolling process, it is only polished after the product finished. In the process of wall reduction, the defect can only get partially eliminated.

Welded steel pipe made by hot rolled coil as raw material, the surface quality of coil is just the pipe’s surface quality, and easy to control.The surface of hot rolled coil have high quality.

So Welded steel pipe surface quality is much better than seamless steel pipe.

2）Molding process differences

Seamless steel pipe can be formed one time in the rolling process.

Welded steel pipe is manufacturing with steel strip or steel plate, through bending and different welding processes.

3）Performance and Usage

Seamless steel pipe has better pressure capacity, strength is higher than ERW welded steel pipe. So it is widely applied in high pressure equipment, and thermal, boiler industries.

Generally the welding seam of the welded steel pipe is the weak point, the quality affect overall performance.

In general, welded steel pipes can withhold 20% less working pressure than seamless ones. This reliability is the prime factor why people go for seamless steel pipe. As a matter of fact, all the industrial pipelines are done with seamless pipes only because the pipes undergo extreme thermal, chemical and mechanical workloads. Welded pipes are more preferred in aerospace, automobile and electronics industries where the budget is comparatively low, and so is the work pressure put on the pipes.

 4）Available Sizes differences

For most of seamless steel pipe manufacturers in China, they produce original seamless pipe sizes maximum OD in 20 inch, 508 mm. Where usually is smaller than 16 inch, 406.4 mm, because of the equipment limits. And if client would like to purchase the seamless steel pipe more than above sizes, then hot expanding machining shall be used. But usually this kind hot expanded seamless steel pipe quality could not compare with the original seamless steel pipe.

On the contrary, welded steel pipe don’t have these limitations, sizes available from 1-1/2 inch 48.3mm to 100 inch 2540 mm.

5）Cost and prices

Usually the seamless steel pipe cost is higher than welded steel pipes, because the raw material, manufacturing equipment and processes. But sometimes by the market pressure, welded pipe is more expensive, so if you met this situation, don’t hesitate to purchase the seamless steel pipe for the same dimensions. 

Welded pipe manufacture process

Welded pipe starts out as a long, coiled ribbon of steel called a skelp. The skelp is cut to the desired length, resulting in a flat rectangular sheet. The width of that sheet’s shorter ends will become the pipe’s outside circumference, a value that can be used to calculate its eventual outside diameter.

The rectangular sheets are fed through a rolling machine that curls the longer sides up toward one another, forming a cylinder. In the ERW process, high-frequency electrical current is passed between the edges, causing them to melt and fuse together.

An advantage of ERW pipe is that no fusion metals are used and the weld seam cannot be seen or felt. That’s opposed to double submerged arc welding (DSAW), which leaves behind an obvious weld bead that must then be eliminated depending on the application.

Welded pipe manufacturing techniques have improved over the years. Perhaps the most important advancement has been the switch to high-frequency electric currents for welding. Prior to the 1970s, low-frequency current was used. Weld seams produced from low-frequency ERW were more prone to corrosion and seam failure.

Most welded pipe types require heat treatment after manufacture.

ERW pipes are manufactured using steel coils: the coil is first uncoiled, then smoothed, cut and, finally formed into a pipe shape by joining its two extremities electrically.

ERW pipes are available in sizes between 1/2 and 20 inches, in carbon steel (ASTM A53 is the most common specification) and stainless steel (ASTM A312). In terms of dimensions, the ASME B36.10 and ASME B36.19 are the key reference specifications (API 5L for welded ERW line pipes).

LSAW PIPE (LONGITUDINAL SUBMERGED ARC WELDING)

An LSAW pipe (“submerged arc welding”) is manufactured by cutting, bending and welding steel plates (JCOE process).

LSAW pipes compete with seamless and ERW pipes in the size range between 16 and 24 inches but are “must-go” option for pipelines above 24 inches (as 24 inches is the maximum size for commercial seamless pipes).

The two main types of LSAW pipes are the longitudinal (with a single or double straight seam weld, DSAW) and the spiral type (called, HSAW, SSAW or SAWL pipe). Therefore, the difference between DSAW vs. LSAW is that DSAW pipes have a seam weld in the inside and outside of the pipe, whereas LSAW pipes have a single seam weld on the outer surface.

The difference between LSAW and ERW pipes is that LSAW pipes are produced using steel plates, ERW pipes are manufactured starting from steel coils.

LSAW welded pipes In the oil and gas industry, large-diameter API 5L LSAW pipes are used to transport hydrocarbons over long distances efficiently.

HSAW/SSAW spiral weld pipes are used for non-critical applications, as water transmission and distribution (not for oil & gas).

LSAW Pipe Manufacturing Process

ERW Pipe Manufacturing Process

SSAW Pipe Manufacturing Process

Seamless pipe manufacture process

Seamless piping begins as a solid cylindrical hunk of steel called a billet. While still hot, billets are pierced through the center with a mandrel. The next step is rolling and stretching the hollow billet. The billet is precisely rolled and stretched until it meets the length, diameter and wall thickness as specified by the customer order.

Some seamless pipe types harden as they’re manufactured, so heat treatment after manufacturing is not required. Others do require heat treatment. Consult the specification of the seamless pipe type you’re considering to learn whether it will require heat treatment.

Seamless Pipe Manufacturing Process

SEAMLESS PIPE SIZES

The ASME B36.10 and B36.19 specifications cover the dimensions and weights of seamless pipes for the petrochemical industry (the specs apply to welded pipes too):

· The ASME B36.10specification covers carbon and low-alloy seamless pipes sizes (dimensions and weights) between 1/8 and 24 inches

· The ASME B36.19specification, instead, covers the dimensions and weights of stainless steel, duplex, nickel-alloy seamless and welded pipes

Commercial seamless pipes are designated with a nominal pipe size (representing the approximate fluid conveyance capacity of the pipe) and with a “schedule”, which refers to the thickness of the pipe (the most common are schedule 40, STD, XS, XXS for carbon/alloy pipes, and 10S, 40S and 80S for stainless and nickel alloy pipes).

How to Identify Seamless or ERW Stainless Steel pipes?

To identify that a pipe supplied is seamless or ERW, Simply read the stencil on the side of the pipe

For steel pipe standard ASTM A53,

Type S means seamless.

Type F is furnace but welded,

Type E is Electrical resist welded.

That’s how. It is the easiest way to identify weather pipe is seamless or ERW.

In short, Seamless is marketed on an outdated myth that it does not have flaws but that welded has an inherent flaw throughout the length of each tube, as stated above. Intuitively this concept is easily accepted by purchasers and designers with limited experience with the various products. Each product form and manufacturing method has its own inherent problems and potential defects.

Advantages Of Welded Tubes & Pipes

· Lower cost compared to the equivalent seamless alternative.

· Short lead time.

· Better surface finishing of outside and inside, the internal material surface for welded tubes can be checked prior to manufacture.

· Thinner wall thickness, and more uniform.

· Tighter tolerance.

Advantages Of Seamless Tubes & Pipes

· Heavy and thick wall thickness.

· No weld seam. generally be considered as better properties and corrosion resistance

· Seamless pipes have better ovality, or roundness

How To Choose Tubes & Pipes, Welded Or Seamless?

Despite many advantages with welded tubes, seamless tube is still treated better than welded type, especially used in rough environment, considered as higher strength, higher pressure, and better corrosion resistance.

Depending on specific application and cost aspect, decide which type is better choice to use.

Tubes and pipes can be produced in both seamless and welded types depending on application requirement.

Different application of seamless pipe & seamed (welded) pipe

seam steel pipe: seam steel pipe is mainly used in water supply engineering, petrochemical industry, chemical industry, electric power industry, agricultural irrigation and urban construction. For liquid transportation: water supply and drainage. For gas transportation: gas, steam, liquefied petroleum gas. For structure: pile driving pipe, bridge, wharf, road, building structure pipe, etc.

Seamless steel pipe: seamless steel pipe has hollow cross-section and is widely used for conveying fluid, such as oil, natural gas, gas, water and some solid materials. Compared with solid steel such as round steel, the steel tube is lighter in weight when the bending and torsion strength is the same, so it is a kind of economic section steel.

Hebei Huayang Steel Pipe Co.,Ltd

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