ERW vs Spiral Pipes: What Are the Differences?

what are the differences between electric resistance welded pipes and spiral pipes?

pipes are a common fixture in any type of structure. for residential spaces, pipes can be found in plumbing, hvac, or any fluid exchange system that requires a vessel for transmission. in industries such as oil & gas, as well as petrochemical, pipes are used to transfer crude oil products before heading to the refinery. in all of these applications, choosing between erw pipes vs spiral pipes remains a point of contention. for example, the pipe must meet certain requirements such as pressure, chemical resistance, non-corrosiveness, strength, durability, and many more.

erw pipes and spiral pipes have been the top choices for a variety of applications. while both pipes can be found in pipeline networks in petrochemical industries, there are a few key differences in the manufacturing process, pressure resistance, surface quality, presence of defects, and performance. although both types also involve welding, the difference in the production method largely affects how well each pipe can be subjected to extreme environmental duress. 

manufacturing process

as mentioned before, the manufacturing process for spiral pipes and erw pipes is different. erw pipes begin with a strip or coil of steel that passes through a roller machine. on the other hand, spiral pipes begin with coiled steel which is winded at a certain angle. while the weld for the erw (electric resistance welded) pipe appears longitudinally, the spiral pipe weld appears as a helix-shaped structure outside of the pipe.

here is a more detailed explanation of each step in the erw pipe-making process:

a coil of steel is hot-rolled through a roller machine. this results in a gauged metal with two visible ends.

the ends are brought together using a process known as electric resistance welding. this joins the two separate ends together using electric current for both the inside and outside of the pipe, without any need for a flux or weld filler.

after the two joints have been combined, the pipe undergoes primary ultrasonic inspection — a form of non-destructive testing that helps in the detection of any cracks or damages on the pipe during the manufacturing process.

post-processing techniques such as annealing and cooling are done to manipulate the pipe’s microstructure, making it more ductile.

the erw pipe is cut to size and finally straightened to ensure uniformity in the surface.

in the production process of spiral pipes, each phase is also outlined below:

spiral pipe-making starts off with an unrolled steel coil that’s unwound with the help of a roller machine. unlike erw pipes, spiral pipes require a welding wire or filler that’s used to produce heat infusing the metals together.

forming a helix-like appearance, the ends of the strips are joined together using a submerged arc welding technique.

each welded portion is inspected so that there are no defects on the pipe. this is made possible using a weld gap control device which is used for weld gap and diameter inspection.

similar to erw pipes, ultrasonic testing and a range of other non-destructive tests (ndts) may also be done to examine the physical properties, weld quality, and chemical composition of the pipe, among others.

pressure resistance

starting off with a strip or coil of metal, both erw pipes and spiral pipes involve stages in production that cause stress on the product, even during end-use. this is known as “residual stress” or leftover stress present on the pipes, even when there are no external forces that are applied in the material.

as much as possible, you want to choose an erw pipe because it results in lower residual stress compared to the spiral pipe. a contributing factor to this is the longitudinal and straight seam electric welding which lowers the residual stress on the pipe. in addition to this, the post-processing done on the erw pipe greatly reduces the stress levels. this is important during storage and use, where the single seam does not play a factor in the quality of the pipe.

due to the spiral rotation in spiral pipes, on the other hand, the residual stress is likely higher. in some cases, this may even cause the pipe to go well beyond its yield limit. when the pipe is already in-service, the combination of tensile & circumferential stresses, plus other forces significantly affects the pipe’s load-bearing capabilities — especially for its multiple seams. the welding technique may also be a factor, since the use of fillers and welding rods may lead to the presence of weld defects and other physical deformations.

performance

with all of the above considerations, erw pipes lead to better performances during use. the single-seam not only allows for a consistent flow of different fluids but also lowers the possibility for incidents such as leaks and bursts. compare this to the multiple seams present in the spiral pipes, which may lead to inconsistent pressure changes that may affect one portion or the entire pipe itself.

aside from this, the multiple welded seams in spiral pipes may cause future issues on calcium build-ups and other chemical deposits. these unwanted substances can reduce the corrosion-resistance of the pipe, lowering its shelf life, and making it less cost-efficient in the long run. whereas in erw pipes, the absence of weld filler raw materials and flux results in more consistent weld quality, thereby improving both surface finish and corrosion resistance.