Comparing an ERW pipe, ie electric resistance welding pipe to a seamless pipe can be both simple and quite complicated depending on how deep into the specifics of each type you want to get. So, ERW vs seamless pipe – what are the characteristics of each type, how are they different, and which should you choose for your project? Let’s find out below.
What is an ERW stainless steel pipe?
ERW or Welded pipes with electrical resistance are stainless steel pipes made from strips or coils of steel that have then been welded longitudinally into pipes. ERW pipe diameters can be anywhere from 2 3/8 to 24 inches, but no larger than 24 inches, as the circumference of the pipe is dictated by the width of the steel strip or coil from which it is made.
When an ERW pipe is cold formed from a steel strip, it is drawn through a series of rollers into a tube. It is then fused with an electrical charge. Here is a nice video that illustrates the whole process.
Due to the way they are created, ERW pipes always have a longitudinal seam running through them that shows how the pipe was manufactured. The weld seam is not visible to the naked eye, but unlike some other types of welding processes such as double submerged arc welding which leaves a clear welded cord.
ERW pipe seams do not require filler metals added to the base material, as contact welding is done by simply heating the edges of the steel plates with a high frequency current.
Thanks to this manufacturing process, ERW pipes have impressive strength and durability, their price is quite affordable, and their production is safe and easy.
However, because there is a welded joint, even if it is imperceptible, ERW pipes do not withstand major pressure like the seamless pipes we will discuss next. So ERW pipes are mostly used for medium or low pressure applications such as water and oil transport.
What is a seamless stainless steel pipe?
As the name suggests, seamless stainless steel pipes they are pipes made without welding points, joints or seams. Instead, the way they are made is by heating a solid billet of steel and pouring it over a punch rod to form a hollow billet tube.
The main benefit of this process is precisely the lack of welding current. This is essential because the weld zone in the cross section of ERP steel pipes is their weakest point. The lack of a seam gives these pipes a much higher resistance to corrosion. This is because while ERW steel pipe is manufactured, it is also corrosion resistant, the weld bead is not, even though it is also 100% steel.
Having no such weakness, seamless pipes have a much higher overall durability and can be used in areas and for purposes that exert greater pressure on pipes, such as hydrocarbon industries and refineries, onshore and offshore oil and natural gas pipelines, drilling, exploration and transportation, automotive, boilers, bearings, hydraulic and air cylinders, and others.
However, this higher mechanical strength also comes with some disadvantages, such as a more complicated manufacturing process, much higher price, occasional inconsistent wall thicknesses, and more.
ERW vs Seamless Pipe – Head to Head Comparison
ERW steel pipe and seamless steel pipe both come in the most common sizes and a variety of lengths. They are also usable in many different areas and for many different jobs, but the welding process used to make ERW pipe is the key distinguishing factor between the two, as the presence of a welded seam slightly compromises the pipe’s structural integrity and strength.
In essence, a pipe is only as strong under pressure as its weakest part, and the weld seam is the weakest part of ERW pipes – both when it comes to pressure and when it comes to corrosion. On the other hand, with seamless pipes, this disadvantage is simply not present.
However, it is important not to overstate the significance of an ERW seam, as these pipes are still capable of withstanding impressive degrees of pressure. In addition, recent technological improvements have continued to make new generations of ERW pipes better than before and the difference between ERW and seamless pipes increases from year to year.
https://www.youtube.com/watch?v=gZV65hd2Czc
So let’s go over some key areas of the comparison between ERW and seamless pipe:
1. Initial cost
Because the ERW stainless steel pipe manufacturing process is so easy, safer, Faster, and cost effective, the pipes themselves are also much more affordable than their seamless counterparts. Of course, final prices may vary between different manufacturers, but here it is an example from a major pipe manufacturer:
- 1” Seamless Pipe (Grade A53 B) – $966/ton
- 14” Seamless Pipe (Grade A53 B) – $855/ton
- 1” ERW Pipe (Grade A53 B) – $588/ Ton
- 14” ERW Pipe (Grade A53 B) – $604/ Ton
As you can see, in many cases the prices of seamless pipe can be up to 150% or more than that of ERW pipe of the same quality. This difference becomes even more significant if you want to buy large quantities of pipes.
2. Resistance to pressure
The exact pressure rating of each pipe must be noted on the pipe itself. Each pipe has its own pressure level, which can vary greatly depending on the details of the pipe, such as wall thickness, its diameter, and so on. In general, however, seamless pipe has a higher pressure than ERW pipe.
Usually the pressure values are calculated by Barlow’s formula which calculates the allowable stress of each pipe relative to its yield strength (measured in psi) and design factor.
In short, you can expect most seamless pipe to be used for high pressure work such as oil and gas pipelines, while ERW pipe is usually preferred for low and medium pressure situations because it is sufficiently good for those that are at the same time more accessible.
3. Corrosion resistance
All steel pipes are expected to be corrosion resistant but ERW pipes can have problems with this because their seams can slowly degrade over long periods of time when exposed to corrosion. This makes ERW and other types of welded pipe immediately disqualified from certain uses in favor of seamless pipe.
How to tell the difference between ERW and seamless pipe yourself?
1. Look at pipe standards and specifications
The easiest way to identify the type of pipe you are looking at is to look at the pipe standards and specifications template on the side of the pipe. So, for example, if the template says you’re looking at an ASTM A53, that’s a seamless pipe because the «S» in the name stands for «stainless.»
Similarly, if the pipe template says it is Type E, it means the pipe is made with electric resistance welding, ie ERW. And, if the template says type F, the pipe is welded in the furnace.
2. Use UV screening
If you can’t look at the template for any reason, another method find out what type the pipe is is to use UV examination. Simply use the UV light to observe the granular structure of a part of the pipe.
If it is an ERW pipe, you should be able to see a noticeable difference in the grain structure where the seam is, even if it is not visible to the naked eye. A seamless pipe, on the other hand, will have the same structure throughout its cross section.
3. Look for professionals
If you can’t find the seam with the UV light, but still aren’t 100% sure what you have is seamless pipe, it’s best to consult with a professional before using the pipe for anything. A professional inspection will be able to tell you exactly what the pipe is, what its specifications are, and what you can safely use it for.
In conclusion – ERW vs seamless pipe
The choice between an ERW pipe and a seamless pipe is more complicated than just «price affordability vs quality», even though most people try to present it that way. Yes, ERW pipes cost less and their weld seam can be a problem in some cases, but the manufacturing process of ERW pipes has come a long way in the last few years and they are of a much higher quality than they used to be.
So when you read about «ERW stainless steel pipe limitations» online or listen to certain experts, it’s important to remember that their information is often outdated. In addition, each manufacturer produces pipes with different specifications. So both seamless and ERW pipes can vary greatly in quality depending on who you get them from.
In other words – to get the best pipe for the job, you should know exactly what you need and the exact specifications of the pipe you are getting, whether it is ERW or seamless pipe. For most residential needs, a high quality ERW pipe should work well as long as the risk of corrosion or high pressure accidents is not present.
