ASTM A358 Stainless Steel EFW Pipe: Grades and Uses

Overview of ASTM A358

ASTM A358 is the standard specification for electric-fusion-welded austenitic chromium-nickel stainless steel pipe for high-temperature, high-pressure and general corrosive service. The pipe is produced by forming plate or sheet into a cylinder and welding the longitudinal seam using an electric fusion welding process such as high-frequency resistance welding or induction welding, after which the pipe may be cold worked or heat treated as required. The standard is widely used for large-diameter piping in power plants, petrochemical plants and process industries where a seamless pipe of the required size would be uneconomical or unavailable.

Key characteristics of A358 pipe are high dimensional accuracy, excellent weld joint performance, resistance to high-temperature oxidation and corrosion, and suitability for severe service conditions. Because the base material is plate, the pipe can be supplied in very large diameters with controlled wall thickness.

Main Grades and Chemical Composition

The table below summarises the principal grades covered by A358 and their key composition.

Grade	Equivalent	Key Composition, %	Characteristics
304 (S30400)	304	Cr 18-20, Ni 8-10, C max 0.08	General-purpose austenitic grade, cost-effective, good atmospheric and mild corrosion resistance.
304L (S30403)	Low-carbon 304	Cr 18-20, Ni 8-12, C max 0.03	Ultra-low carbon, avoids intergranular corrosion after welding.
316 (S31600)	316	Cr 16-18, Ni 10-14, Mo 2-3, C max 0.08	Molybdenum improves resistance to chlorides, seawater and salt solutions.
316L (S31603)	Low-carbon 316	Cr 16-18, Ni 10-14, Mo 2-3, C max 0.03	Combines molybdenum resistance with low carbon for welded service.
321 (S32100)	Titanium stabilised	Cr 17-19, Ni 9-12, Ti min 5 x C, C max 0.08	Titanium prevents carbide precipitation; ideal for 430-870 C service.
347 (S34700)	Niobium stabilised	Cr 18-20, Ni 9-13, Nb min 10 x C, C max 0.08	Niobium stabilised; oxidation resistance in the 870-980 C range.

Typical Mechanical Properties

Room-temperature minimum mechanical properties of the common grades are listed below.

Property	304/304L	316/316L	321/347
Tensile strength, MPa	515 min	515 min	515 min
Yield strength, MPa	205 min	205 min	205 min
Elongation, %	30 min	30 min	30 min
Strength at 500 C, MPa	140 min	150 min	160 min

Corrosion and High-Temperature Resistance

The austenitic matrix is face-centred cubic, non-magnetic and resistant to air, water, neutral salt solutions and many organic acids such as nitric acid. Molybdenum in the 316 series improves resistance to chloride attack in seawater and hydrochloric acid service. Titanium and niobium in the 321 and 347 grades bind carbon and prevent chromium carbide precipitation, which eliminates intergranular corrosion in welded or high-temperature service. Maximum continuous service temperatures are about 870 C for 304 and 304L, 925 C for 316 and 316L, and 980 C for 321 and 347, with short-term exposure allowed somewhat higher for oxidation resistance.

Manufacturing and Quality Control

Pipe is manufactured by electric fusion welding using methods such as high-frequency resistance welding or induction welding, and may be cold drawn or annealed afterwards. Stress relief or solution annealing restores full corrosion resistance after welding. Inspection includes radiographic or ultrasonic testing of the weld, a hydrostatic test with a minimum pressure of about 2.4 MPa calculated from the pipe dimensions, and, for low-carbon grades such as 304L and 316L, an intergranular corrosion test according to ASTM A262 Practice E to validate post-weld corrosion resistance.

Comparison with Related Standards

Standard	Main Differences
ASTM A312	Covers both seamless and welded pipe for general service, not limited to high-temperature or high-pressure duty.
ASTM A213	Covers seamless boiler, superheater and heat-exchanger tubes, with emphasis on high-temperature strength grades.
ASTM A790	Covers welded duplex stainless steel pipe, combining high strength with excellent corrosion resistance.

Typical Applications

Petrochemical industry: furnace tubes, reactor piping and heat exchangers.

Power generation: boiler superheater and reheater piping.

Pharmaceutical and food processing: high-purity media transport lines.

Environmental equipment: flue gas treatment and denitrification piping.

Marine engineering: seawater cooling lines, with 316L for pitting resistance.

Frequently Asked Questions

What does EFW mean?

EFW stands for electric fusion welding, a process in which the longitudinal seam of the pipe is fused by an electric welding method, typically high-frequency resistance welding or induction welding, without the addition of filler metal in the HFRW variant.

Is A358 pipe seamless or welded?

A358 pipe is welded, produced from plate or sheet. If a seamless product is required, specifications such as A312 or A213 apply.

What is the difference between ASTM A358 and ASTM A312?

A312 covers both seamless and welded austenitic pipe in a broad range of sizes for general corrosive service, while A358 is limited to electric-fusion-welded pipe made from plate, typically in larger diameters for high-temperature and high-pressure duty.

Which grade should be selected for seawater service?

316L is the usual choice for seawater and chloride-bearing water because of its molybdenum content, and 317L can be considered where crevice corrosion resistance must be maximised.

Why is the ASTM A262 Practice E test important?

Practice E is the copper-copper sulfate test for susceptibility to intergranular attack; it confirms that low-carbon grades such as 304L and 316L remain corrosion-resistant after welding, which is essential for process piping.