What is a Seamless pipe?
Seamless pipe is made from a round steel billet (solid cylindrical hunk of steel that is cast from raw steel). This billet is then heated, stretched out and pushed or pulled over a form. It is then pierced through the center with a die and mandrel which increases the inside diameter and reduces the outside diameter. Even though seamless pipes are manufactured in a variety of sizes, with an increase in pipe diameter the production cost increases. The name seamless comes from its absence of a seam. Seamless pipes are widely used in process piping, power piping, shipbuilding, pressure vessel, construction, and chemical industries.
What is a Welded Pipe?
Welded pipe is made by cold forming flat strip, sheet or plates into a round or circular shape by a roller or plate bending machine. The pipe is then welded with or without filler material using a high energy source. Welded pipes can be produced in large sizes without any size restriction. Welded pipes are normally used for transportation of water, oil or gases in large quantities.
Seamless vs Welded Pipe
From the above paragraphs, it is obvious that seamless and welded pipes differ in their manufacturing process. The other differences are listed in the below-attached table.
|Sr. No||Parameter||Seamless Pipe||Welded Pipe|
|1||Strength||Able to withstand more pressure and load as there is no weak seam.||Due to welding they are believed to withstand 20% less pressure and load as compared to seamless pipe.|
|2||Length||Relatively shorter in length due to manufacturing difficulties.||Can be manufactured in long continuous lengths.|
|3||Size||Manufactured for nominal size 24 inch or less.||No such size restriction on production.|
|4||Corrosion Resistance||Less prone to corrosion, means more corrosion resistant.||Weld areas are more prone to corrosion attacks, means less corrosion resistance.|
|5||Surface Quality||Rough due to extrusion process||Smooth high quality surface as compared to seamless pipe.|
|7||Production Process||Complex, long procurement lead time||Simpler, short procurement lead time.|
|8||Tests||Seamless pipes does not require testing for weld integrity.||Must be tested before use.|
|9||Application||Suitable for high presure temperature and corrosive environment||Normally used for less corrosive and low pressure environment.|
|10||Availability||Less available, limited material types, longer delivery time||Readily available for various different materials; shorter delivery time|
|11||Wall Thickness||Inconsistent wall thickness across length, thicker so heavier||Wall thickness more consistent than seamless ones, thinner|
|12||Ovality||Better ovality, roundness||Poor ovality and roundness as compared to seamless counterpart.|
|13||Internal surface check||Checking not possible||Internal surface can be checked before manufacturing|
Pipe Selection, Welded or Seamless?
Even though improved manufacturing methods of recent time can produce welded pipes comparable to seamless pipes, still the seamless pipes are preferred in a maximum of the cases. However, for large size piping applications (>24 inch NPS) welded pipes are mostly preferred due to less cost. Along with cost various other parameters like diameter to thickness ratio, availability, corrosion resistance, etc. are considered for pipe selection.