What Is Heat-Resistant Stainless Steel Pipe?

1. What Is a Heat-Resistant Stainless Steel Pipe?

A heat-resistant stainless steel pipe is a tubular product intended for service at elevated temperatures, typically above 550 C, where the material must resist oxidation, scaling and loss of load-bearing capacity. Chromium is the essential element: it forms a stable, adherent oxide film that protects the metal surface at high temperature. Nickel and, in some grades, stabilizing elements such as titanium or niobium are added to improve high-temperature strength, creep resistance and weldability. Heat-resistant pipes are used to carry hot gases, steam and process media in boilers, furnaces, heat exchangers and refineries.

2. Main Grades and Their Selection

Grade selection depends on the service temperature, the atmosphere and the mechanical loads. The table below summarizes the common austenitic grades and their typical continuous-service oxidation limits.

Grade	Chromium / Nickel (wt %)	Key Feature
304H	18.0-20.0 / 8.0-10.5	Carbon 0.04-0.10% for improved creep strength above 500 C
309S	22.0-24.0 / 12.0-15.0	Oxidation resistance up to about 980 C
310S	24.0-26.0 / 19.0-22.0	Oxidation resistance up to about 1050 C
321H	17.0-19.0 / 9.0-12.0	Titanium-stabilized, carbon 0.04-0.10%
347H	17.0-19.0 / 9.0-13.0	Niobium-stabilized, carbon 0.04-0.10%

304H is selected for superheater and reheater service where creep strength governs. 309S and 310S are chosen where oxidation resistance at high temperature is the dominant requirement. 321H and 347H resist sensitization during service in the 425-900 C range because titanium or niobium combines with carbon preferentially, preventing chromium carbide precipitation at grain boundaries.

3. Relevant Product Standards

The main product standards for heat-resistant stainless steel pipes and tubes are:

ASTM A213/A213M: seamless ferritic and austenitic boiler, superheater and heat-exchanger tubes

ASTM A249/A249M: welded austenitic boiler, superheater, heat-exchanger and condenser tubes

ASTM A312/A312M: seamless, welded and heavily cold-worked austenitic pipe

ASTM A450/A450M: general requirements for carbon, ferritic alloy and austenitic tubes

EN 10216-5: seamless stainless steel tubes for pressure purposes

Commercially common ranges for these heat-resistant tubes are about 6.35-76.2 mm outside diameter with wall thicknesses of about 0.91-3.25 mm, although ASTM A213 permits larger sizes up to 127 mm nominal outside diameter.

4. Testing and Inspection

ASTM A450 sets the general requirements for tube dimensions, straightness, surface condition and testing. Hydrostatic testing is performed on each tube to the pressure required by the standard, and where specified, nondestructive examination such as eddy-current testing per ASTM E213 or ultrasonic testing is applied to confirm freedom from harmful discontinuities. Each tube is also visually inspected for surface defects, and the chemical composition and mechanical properties are verified on representative samples per the product standard.

5. Typical Applications

Superheater, reheater and boiler tubes in power generation

Furnace radiant tubes and process heater coils in refineries and petrochemical plants

Heat-exchanger tubes for hot gases and aggressive process media

Reformer and cracking furnace tubes

Exhaust and aftertreatment piping in high-temperature industrial processes

Frequently Asked Questions

What temperature can heat-resistant stainless steel pipe withstand? Continuous oxidation resistance depends on the grade: about 980 C for 309S and about 1050 C for 310S in air. For pressurized service the allowable temperature is lower and is governed by the design code and creep properties.

What does the H in 304H mean? H denotes a controlled carbon range of 0.04-0.10%, which provides higher creep strength at elevated temperature than the standard low-carbon grades. H grades are required for many boiler and heater applications.

What is the difference between 321H and 347H? Both are stabilized grades with a controlled carbon range of 0.04-0.10%. 321H is stabilized with titanium and 347H with niobium. 347H is sometimes preferred where the material is held in the sensitizing temperature range for long periods.

Are heat-resistant pipes seamless or welded? Both forms are available. ASTM A213 covers seamless tubes, ASTM A249 covers welded tubes, and ASTM A312 covers both seamless and welded pipe. The choice depends on size, pressure rating and cost.

Why is chromium important in heat-resistant pipes? Chromium forms a stable, adherent oxide film on the surface at high temperature. This film slows further oxidation and scaling, which is why chromium content is the first criterion when selecting a heat-resistant grade.