Seamless vs Welded Steel Pipe How to Choose the Right Route

How Each Pipe Is Made

Seamless steel pipe is a long pipe of steel with a hollow section and no joint around it. Because there is no weld line there is no seam to qualify, inspect or coat differently from the body of the pipe.

Welded pipe is formed from plate or strip and closed with a seam. ERW pipe is electric resistance welded and is used for low pressure liquid transportation such as water, gas and oil as well as oil drilling and machinery manufacturing. LSAW pipe is longitudinal submerged arc welded. SSAW pipe is spiral submerged arc welded and is used for low pressure liquid transportation and for construction and piping.

• Seamless hollow section with no joint around the pipe
• ERW electric resistance welded for water gas and oil service
• LSAW longitudinal submerged arc welded for larger diameters
• SSAW spiral submerged arc welded for the largest diameters and construction piling

Diameter and Wall Thickness Ranges Compared

Diameter is the fastest way to narrow the choice, because the three welded routes each cover a different band and they overlap only at the edges.

Seamless pipe is supplied to schedule rather than to a single wall figure, running SCH5S, SCH10S, SCH20S, SCH20, SCH30, STD, SCH40, SCH60, SCH80, SCH100, SCH140, SCH160 and XS, which covers 1.65mm to 80mm of wall. Standard lengths are 5.8m and 6m fixed, 12m fixed, or 2 to 12m random, or customized.

• ERW outside diameter 21.3mm to 660.4mm which is 1/2 inch to 26 inch wall 1.5 to 22.2mm length 0.3 to 18 M
• LSAW outside diameter 355.6mm to 1820mm wall 5.0 to 50mm length 3 to 12.5m
• SSAW outside diameter 219.1mm to 3048mm which is 8 inch to 120 inch wall 4mm to 30mm length 3 to 70 M
• Seamless wall by schedule SCH5S through SCH160 and XS covering 1.65mm to 80mm
• Seamless lengths 5.8m 6m fixed 12m fixed and 2 to 12m random

Standards and Grades Behind Each Route

The standard your project is written against often decides the route before any engineering comparison happens. Seamless line pipe is supplied to API 5L, ASTM A106, ASTM A53, DIN17204, DIN17440, DIN2448 and JISG3452-54 in grades including A53B, A106B and API 5L B, X42, X46, X52, X60 and X65.

ERW pipe is supplied to ASTM 53, EN10217, DIN 2458, IS 3589, JIS G3452 and BS1387. LSAW adds GB/T3091 and GB/T9711 to that list. SSAW is supplied to ASTM A252, EN10217-1,2,5 and EN10219-1 together with BS, JIS and IS, in ASTM A252 GR 1, GR 2 and GR 3 or BS 4360 Grade 43 and Grade 50.

• Seamless line pipe API 5L ASTM A106 ASTM A53 DIN2448 JISG3452-54
• Seamless casing API 5CT GB/T 19830 SY/T 6194 in H40 J55 K55 N80 L80 13Cr C90 T95 P110
• ERW and LSAW EN grades S275 S275JR S355JRH S355J2H
• ERW and LSAW GB grades Q195 Q215 Q235 Q345 and L175 L210 L245 L320 to L555
• SSAW certificates EN10217 EN10219 API 5L PSL1 PSL2 and API 5CT

Pressure Duty and Precision Work

ERW, LSAW and SSAW pipe are all described for low pressure liquid delivery such as water, gas and oil. Seamless pipe carries the same media but also covers the drilling and casing duties, with drill pipe supplied to API SPEC 5DP and API SPEC7 in G105 or S135 with Nc38 and Nc50 connections, and casing supplied to API 5CT and GB/T 19830.

Where dimensional precision rather than pressure is the requirement, precision seamless tube is the answer. It is produced by cold drawing or cold rolling, and its internal and external diameter can be accurate to within 0.2mm, in outside diameters from 10mm to 500mm and wall thickness 2 to 50mm, to GB/T8713-88, GB/T3639-2009, DIN2391 and EN10305 in ST52, Q345B, CK20, CK45 and SAE1026.

• Welded pipe described for low pressure water gas and oil transportation
• Seamless pipe additionally covers drill pipe and casing duty
• Precision seamless tube accurate to within 0.2mm on inside and outside diameter
• Precision tube outside diameter 10mm to 500mm wall 2 to 50mm
• Precision tube used for mechanical parts engineering structures barrels shells and bearings

Testing and Certification on Delivery

Welded line pipe is tested more visibly than seamless because the seam has to be proved. ERW pipe is tested by chemical component analysis, mechanical properties covering ultimate tensile strength, yield strength and elongation, technical properties covering flattening, bending, blow and impact tests, exterior size inspection and hydrostatic test. LSAW adds an X-ray test.

SSAW pipe is tested by chemical component analysis, mechanical properties covering tensile strength, yield strength and elongation, a metallographic test, and technical properties covering bending, Charpy V impact, hydrostatic and X-ray tests. ERW and LSAW pipe are certified to EN 10204/3.1Ba.

• Chemical component analysis on all welded routes
• Mechanical properties tensile strength yield strength elongation
• Flattening bending blow and impact tests on ERW
• Hydrostatic test and X-ray test on LSAW and SSAW
• Certificate EN 10204/3.1Ba on ERW and LSAW pipe
• Supplier certifications ISO9001 BV SGS RoHS and API 5L on line pipe

Coating and End Finish

Coating options are largely shared across the routes, so the coating specification rarely decides between seamless and welded. Welded line pipe is offered with fusion bond epoxy coating, coal tar epoxy, 3PE, varnish coating, bitumen coating and black oil coating as required.

Seamless pipe is supplied black painted, galvanized, natural, 3PE anticorrosive coated or with polyurethane foam insulation, and casing adds varnish, transparent oil, hot galvanized, epoxy coating, BE and PE. Seamless pipeline pipe ends are beveled above 2 inch and plain at 2 inch and below, with plastic caps or screwed and socket ends available.

• Fusion bond epoxy coal tar epoxy 3PE varnish bitumen and black oil coatings on welded pipe
• Black painted galvanized natural 3PE and polyurethane foam insulation on seamless pipe
• Bevel end above 2 inch plain end at 2 inch and below
• Plastic caps or screwed and socket ends on request
• Galvanized seamless and galvanized welded pipe available in the same size bands

How to Choose in Practice

Start with diameter and wall. If the line sits between 21.3mm and 660.4mm and the duty is low pressure water, gas or oil, ERW is usually the economical answer. Above that, LSAW covers up to 1820mm and SSAW up to 3048mm for transmission and piling work.

Choose seamless where the specification names API 5L, ASTM A106 or API 5CT, where the wall has to go up to 80mm by schedule, where the service is drilling or casing, or where the precision tube tolerance of 0.2mm is the reason for the order in the first place.

• Small to medium diameter low pressure lines choose ERW
• Large diameter transmission lines choose LSAW
• Very large diameter water lines and piling choose SSAW
• Drilling casing and heavy wall schedules choose seamless
• Precision mechanical parts choose cold drawn precision seamless tube
• Name the standard and the coating on the inquiry so the route is fixed before pricing