I. Materials and steel grades of seamless steel pipes and welded steel pipes
Seamless steel pipes and welded steel pipes use different materials and steel grades according to their uses and requirements. Common ones include:
1. Seamless steel pipes
Seamless steel pipes are usually used in high-pressure and high-temperature resistant applications, so high strength and good corrosion resistance are required.
Common materials: carbon structural steel, low alloy steel, stainless steel, etc.
Common steel grades:
Chinese standard (GB): 20#, 45#, Q345B, 10CrMo910, 12Cr1MoVG, 1Cr5Mo.
American standard (ASTM): A106 Gr.B, A53 Gr.B, A335 P11, P22.
European standard (EN): S355J2H, P235GH, P355NH.
2. Welded steel pipes
Welded steel pipes are suitable for low-pressure occasions, and their material range is relatively wider.
Common materials: carbon steel, alloy steel, stainless steel.
Common steel grades:
Chinese Standard (GB): Q195, Q235A/B, Q355B.
American Standard (ASTM): A53 Gr.B, A500 Gr.B, A252.
European Standard (EN): S235JR, S275JR, S355JR.

II. Steel pipe standards of various countries
The production and use of steel pipes need to follow standards, and countries and international organizations have detailed regulations.

Chinese Standard (GB)
GB/T 8163: Seamless steel pipes for conveying fluids.
GB/T 9711: Steel pipes for conveying in the petroleum and natural gas industry.
GB/T 3091: Welded steel pipes for low-pressure fluid conveying.
American Standard (ASTM/API)
ASTM A106: Seamless carbon steel pipes for high temperature service.
ASTM A53: Seamless and welded steel pipes for pipelines.
API 5L: Steel pipes for conveying pipelines.
European Standard (EN)
EN 10210: Hot-formed seamless and welded steel pipes for structures.
EN 10219: Cold-formed welded structural pipes.
Japanese Standard (JIS)
JIS G3454: Seamless steel pipes for medium and low pressure fluid transportation.
JIS G3466: Square and rectangular welded steel pipes.

III. Conventional size specifications
The specifications of steel pipes are mainly based on outer diameter and wall thickness.
1. Seamless steel pipe
Outer diameter range: 6mm–600mm.
Wall thickness range: 1mm–60mm.
Common length: standard length 6m, 12m, or customized according to customer requirements.
2. Welded steel pipe
Outer diameter range: 21.3mm–8000mm (especially spiral welded pipe).
Wall thickness range: 2mm–25mm.
Common length: 6m, 12m, spiral welded pipe can produce longer lengths.

4. Selection and use of seamless steel pipes and welded steel pipes
1. Selection basis
Seamless steel pipes:Application scenarios need to withstand high pressure, high temperature, or extreme environment, such as boiler tubes and heat exchanger tubes. Occasions with high requirements for dimensional accuracy and mechanical properties.
Welded steel pipes:Used in low-pressure or medium-low-pressure scenarios, such as water supply pipes and building support pipes. It is preferred when the project budget is limited and there are no harsh environmental requirements.

2. Respective uses
Uses of seamless steel pipes:
Industrial fields: petroleum, chemical, electric power, boilers, heat exchangers.
Machining: automobile drive shafts, bearing rings.
Special uses: high-pressure boiler tubes, high-temperature alloy tubes.
Uses of welded steel pipes:
Construction engineering: scaffolding pipes, steel structure supports.
Municipal and energy engineering: water supply and drainage pipelines, natural gas transmission pipelines.
Agriculture and industry: irrigation pipes, coal mine transmission pipes.

Seamless steel pipes and welded steel pipes have their own advantages in material, specifications and uses. Seamless steel pipes are suitable for demanding, high-performance applications, while welded steel pipes offer advantages in cost and a large size range.