Seamless vs welded pipe – What Is Piping

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. Fig. 1: Welded vs Seamless Pipe manufacturing 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. NoParameterSeamless PipeWelded Pipe1StrengthAble 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.2LengthRelatively shorter in length due to manufacturing difficulties.Can be manufactured in long continuous lengths.3SizeManufactured for nominal size 24 inch or less.No such size restriction on production.4Corrosion ResistanceLess prone to corrosion, means more corrosion resistant.Weld areas are more prone to corrosion attacks, means less corrosion resistance.5Surface QualityRough due to extrusion processSmooth high quality surface as compared to seamless pipe.6EconomyCostlierMore economic7Production ProcessComplex, long procurement lead timeSimpler, short procurement lead time.8TestsSeamless pipes does not require testing for weld integrity.Must be tested before use.9ApplicationSuitable for high presure temperature and corrosive environmentNormally used for less corrosive and low pressure environment.10AvailabilityLess available, limited material types, longer delivery timeReadily available for various different materials; shorter delivery time11Wall ThicknessInconsistent wall thickness across length, thicker so heavierWall thickness more consistent than seamless ones, thinner12OvalityBetter ovality, roundnessPoor ovality and roundness as compared to seamless counterpart.13Internal surface checkChecking not possibleInternal surface can be checked before manufacturingTable explaining differences between Seamless and Welded Pipes 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. Few more useful resources for you..Other differences between piping terms or itemsPiping Design and Layout BasicsPiping Stress AnalysisMechanical Design BasicsProcess Design BasicsInstrumentation Design BasicsCivil Design BasicsPipeline Design BasicsPiping Material Basics