The Basics of Buying Steel Pipe - Eiffel Trading

There are several variables to consider when buying steel pipe, including the pipe dimension, thickness, and coating, whether the pipe is seamless, straight weld or spiral weld, and whether to purchase new pipe or surplus pipe.

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Steel Pipe Wall Thickness

Steel pipe walls come in three main thickness options: standard (STD), extra strong (XS) and double extra strong (XXS). For example, a steel pipe manufacturer might offer a 10-inch steel pipe with a standard wall thickness of 0.365 inches, an extra strong wall thickness of 0.5 inches, and a double extra strong wall thickness of 1 inch. The best pipe thickness to choose will vary depending on the project requirements and how much stress the pipe is expected to withstand.

Small Diameter vs. Large Diameter Steel Pipe

Because steel is malleable and durable, it can be used to make pipe in a wide range of sizes. Small diameter steel pipe can range from the 1.5 inch tubing used for things like hydraulic lines and instrumentation tubes to the smallest hypodermic needle, which has an inner diameter of 0.mm. Conversely, large diameter steel pipe—such as the pipe used in shipbuilding and the oil and gas industry—starts at about 14 inches and increases up to 36 inches and larger.

Steel Pipe Coating Options

Because steel pipe is prone to oxidation and corrosion, the steel must be protected. One of the most popular and cost effective ways to protect steel pipe is to coat the pipe in a protective finish. Common coating options include fusion bond epoxy, SynergyTM coating, scotch coating/fletcher coating, and galvanizing. Each of these options varies in their use and application, and different coatings will work better in different environments.

Surplus vs. New Steel Pipe

Surplus steel pipe is pipe that has been used before and is being resold. It’s a common misconception that surplus steel pipe must be old or corroded, but this isn’t always the case. Sometimes surplus steel pipe is brand new. New steel pipe might be sold as “used” or “surplus” if the pipe was left over from another project, such as in instances where more pipe was ordered than needed, or where scraps of pipe were left over from being cut. Surplus steel pipe is a cost effective option that works well for light duty structural applications, road bore casings, temporary drainage projects, and more. Surplus steel pipe should only be used for projects where it is both legal and safe; if safety issues arise, then it is best to use new steel pipe.

Seamless vs. Straight Weld vs. Spiral Weld

The three main styles of steel pipe are seamless, straight weld and spiral weld, named for the way in which they are manufactured. Straight weld steel pipe is made by taking a flat sheet of steel and welding the ends together, resulting in a pipe with a single, straight seam down its length. Similarly, spiral weld pipe is also created by taking a flat sheet of steel and welding the ends together, except that the coil is wound at an angle, so the weld around the outside of the pipe runs in the shape of a helix rather than in a straight line. Unlike straight and spiral weld steel pipe, seamless steel pipe is made by stretching steel out into a seamless tube, and therefore the pipe has no seam.

Generally, welded pipe is considered weaker because of its seam, while seamless pipe lacks a weld and is generally considered safer. Seamless pipe is a top choice for high-pressure, high-temperature applications, such as those in oil and gas, power generation and the pharmaceutical industry. The downside of seamless steel pipe is that the rolling and stretching manufacturing process produces an inconsistent wall thickness compared to welded pipe, and it’s also more expensive to buy. Welded pipe is cheaper than seamless pipe and is typically good for lightweight applications such as transporting gas, electrical conduit and plumbing.

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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.

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.

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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.

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