Structural Pipes vs Process Pipes

Steel pipes serve two fundamentally different purposes: carrying fluids (process pipes) and supporting loads (structural pipes). The standards, testing requirements, and material properties differ accordingly. Mixing them up can cause serious engineering and safety issues.

Process pipes must contain internal pressure and resist corrosion from the transported media. Structural pipes must withstand axial loads, bending, and compression. The specifications reflect these different demands.

Feature	Structural Pipe	Process Pipe
Primary function	Load bearing (compression, tension, bending)	Fluid/gas containment (pressure, temperature)
Key standards	ASTM A500, A501, EN 10210, EN 10219	ASTM A106, A53, API 5L, ASTM A312
Design code	AISC 360, EN 1993 (Eurocode 3)	ASME B31.3, B31.1, B31.4, B31.8
Shape	Round, square, rectangular (HSS)	Round only
Sizing	OD x wall thickness	NPS and schedule
Hydrostatic test	Not required	Mandatory per ASTM/API
NDT	Minimal or none	UT, RT on welds; full-body UT
Chemical limits	Broader tolerance	Tighter (especially S, P for sour service)
Mill certificates	EN 10204 2.2 or 3.1	EN 10204 3.1 or 3.2
Traceability	Lot-based	Heat-based (individual heat tracking)
Cost	Lower	Higher

Structural Pipe Standards

Structural hollow sections are manufactured to bear mechanical loads:

• ASTM A500: Cold-formed welded and seamless carbon steel structural tubing (round, square, rectangular). Grades A, B, C, D with yield strengths from 228 to 317 MPa.
• ASTM A501: Hot-formed carbon steel structural tubing.
• EN 10210: Hot-finished structural hollow sections. Grades S235JRH to S460NH.
• EN 10219: Cold-formed welded structural hollow sections.

These pipes are dimensioned by outside diameter and wall thickness (e.g., 219.1 x 8.0 mm), not by NPS and schedule.

Process Pipe Standards

Process pipes are designed for pressure containment and fluid transport:

• ASTM A106: Seamless carbon steel for high-temperature service
• ASTM A53: Welded and seamless carbon steel for general use
• API 5L: Line pipe for oil, gas, and water pipelines
• ASTM A312/A358: Stainless steel pipes

Common Mistake

Never substitute structural pipe (ASTM A500) for process pipe (ASTM A106/API 5L) in pressure-containing service. Structural pipe is not hydrotested, has looser chemical composition limits, and is not designed for internal pressure containment. The reverse substitution (process pipe for structural use) is technically feasible but uneconomical.

Overlap

ASTM A53 Grade B pipe is sometimes used for both structural and low-pressure process applications. It is the one specification that bridges both worlds, as it can be ERW or seamless, is hydrotested, and has adequate mechanical properties for light structural loads.

Read the full guide to pipe types