Steel pipe is a fundamental component in everything from oil & gas transmission to structural supports, water lines, and chemical process systems. But not all steel pipe is created equal.

The grade, seam type, and applicable standards determine a pipe’s strength, corrosion resistance, and suitability for its intended use. In this article, we’ll break down the essentials to help you choose the right pipe — and avoid costly mistakes.

Steel Pipe Grades

A pipe's grade refers to its material composition and mechanical properties. These are typically set by ASTM, ASME or API specifications.

ASTM/ASME A53

• Type E (Electric Resistance Welded) or S (Seamless)

• Grade A or B (Grade B is stronger)

• Common in plumbing, steam, and low-pressure systems

• Suitable for welding, threading, or grooving

ASTM/ASME A106

• Seamless carbon steel pipe

• Grades A, B, and C (B is most common)

• Used for high-temperature service

• Popular in refineries, power plants, and process piping

API 5L

• Seamless or welded line pipe

• Grades like X42 through X80, increasing with yield strength

• Widely used in oil & gas transmission

• Comes in PSL1 and PSL2 levels (PSL2 has tighter tolerance and testing)

ASTM A333

• Seamless and welded steel pipe for low-temperature service

• Commonly used in cryogenic and refrigeration applications

Seam Types: Seamless vs Welded

Seamless Pipe

• Made from solid round billets — no seam

• Offers uniform strength and pressure rating throughout

• Ideal for high-pressure, high-temperature, or critical service

• Higher cost due to more intensive manufacturing

Welded Pipe

• Formed from steel plate, strip, or coil, then welded longitudinally or spiral welded

• Three main types:

  • ERW (Electric Resistance Welded) — for standard pressure applications

  • FW or CW (Continuous Furnace Weld) — for standard pressure applications 4" & below

  • DSAW or SAW (Double/Submerged Arc Welded) — for larger-diameter, high-strength line pipe

• Typically more affordable than seamless

• Slightly lower pressure ratings

Steel Pipe Standards: What They Govern

Industry standards define how steel pipe is manufactured, tested, and classified. Here are the key ones:

Knowing which standard applies is critical — it affects pipe selection, inspection requirements, and even approval from regulatory bodies or engineers of record.

Let Hayward Pipe Help

At Hayward Pipe & Supply Co., we stock and source steel pipe in all grades, sizes, and specs — including:

• A53, A106, A333, API 5L

• Seamless and ERW

• Bare, galvanized, and coated finishes

• MTRs are available upon request

Whether you need line pipe, boiler pipe, or structural steel, our team helps ensure you get the right product, on time, with full traceability.