Differences Between American Standard (ASTM) and Chinese Standard (GB) Pipes

1. Standard System & Scope of Application

2. Dimensional Specification System

Pipe Diameter Labeling

• American Standard: Uses Nominal Pipe Size (NPS) (e.g., NPS 2, NPS 4) in inches, which does not directly correspond to the actual outer diameter (e.g., NPS 2 corresponds to an outer diameter of 60.3mm).
• Chinese Standard: Uses Nominal Diameter (DN) (e.g., DN50, DN100) in millimeters, where the DN value is closer to the pipe’s outer diameter (e.g., DN50 corresponds to an outer diameter of 57mm).

Wall Thickness Series

• American Standard: Adopts the Schedule (Sch) series (e.g., Sch40, Sch80, Sch160). Wall thickness increases with the Sch number, and different Sch values correspond to different wall thicknesses for the same NPS.
• Chinese Standard: Uses wall thickness class (S), pressure class, or directly labels the wall thickness (e.g., φ57×3.5). Some standards also support Sch series labeling.

3. Material Grades & Performance Differences

4. Technical Requirements & Test Standards

Pressure Testing

• American Standard: Hydrostatic testing is a mandatory requirement with stricter test pressure calculation formulas, complying with ASME B31 specifications; non-destructive testing (UT/RT) is required for some high-pressure pipes.
• Chinese Standard: Hydrostatic testing is negotiable on demand with relatively relaxed test pressure; the proportion of non-destructive testing is determined by the pipeline class (e.g., 100% testing for GC1-class pipelines).

Delivery Conditions

• American Standard: Pipes are typically delivered in normalized + tempered condition with clear surface treatment requirements (e.g., pickling, passivation).
• Chinese Standard: Can be delivered in hot-rolled, cold-drawn, normalized, or other conditions with more flexible surface treatment requirements.

5. Compatibility Differences in Connection Methods

• American Standard pipes are matched with fittings (flanges, elbows) complying with ASME B16.5, with flanges commonly using RF (Raised Face) sealing surfaces and pressure classes labeled as Class (e.g., Class 150, Class 300).
• Chinese Standard pipes are matched with fittings complying with GB/T 9112-9124, with flanges labeled by PN (e.g., PN16, PN25) for pressure classes. Sealing surface types are compatible with American Standard but differ slightly in dimensions.

Key Selection Recommendations

1. Prioritize American Standard pipes for international projects; verify that NPS, Sch series, and material certificates meet ASTM requirements.
2. Prioritize Chinese Standard pipes for domestic projects due to lower costs and sufficient supply of supporting fittings.
3. Do not directly mix American Standard and Chinese Standard pipes, especially for flange connections—dimensional mismatches can cause sealing failure.