15CrMo is a low-alloy pearlitic heat-resistant steel defined in the Chinese national grade system and widely produced as seamless pipe for elevated-temperature service. The grade contains approximately 1% chromium and 0.5% molybdenum, which raises creep strength and resistance to hydrogen attack compared with plain carbon steel. Seamless tube in this grade is normally ordered to GB 5310 for high-pressure boiler service or to GB/T 3077 where bar-derived mechanical tube is required, and its chemistry places it in the same 1Cr-0.5Mo family as ASTM A335 P12 and ASTM A213 T12 in international specifications.
Chemical Composition and Mechanical Properties
15CrMo is a fully killed, fine-grain steel supplied in the normalised and tempered condition. Chromium improves oxidation resistance and high-temperature strength, while molybdenum suppresses temper embrittlement and raises the creep rupture limit. A typical specification for pipe product is given below; values follow the GB 5310 / GB/T 3077 requirements for the grade.
| Element | C | Si | Mn | Cr | Mo | P | S |
|---|---|---|---|---|---|---|---|
| Range (%) | 0.12-0.18 | 0.17-0.37 | 0.40-0.70 | 0.80-1.10 | 0.40-0.55 | ≤0.030 | ≤0.030 |
| Property | Tensile strength | Yield strength | Delivery condition |
|---|---|---|---|
| Requirement | 440-640 MPa | ≥295 MPa | Normalised + tempered |
Elongation, impact energy and hardness limits are taken from the ordering standard, and the higher-temperature properties that govern design are the creep rupture and stress rupture values rather than room-temperature tensile data.
Application Fields of 15CrMo Steel Pipe
Power plant boilers: superheaters, reheaters, headers and main steam pipework operating in the 450-540 °C range at pressures up to about 14 MPa. The grade remains the standard choice for subcritical units, where its creep strength supports long design lives measured in decades. Supercritical and ultra-supercritical units move to higher-alloy grades such as T91/P92.
Petrochemical and refining: hydrogenation reactor inlet and outlet lines, convection section tubes of cracking furnaces and high-temperature heat exchanger bundles. Hydrogen service limits follow the Nelson curve of API 941 and hydrogen sulphide service limits follow NACE MR0175, so material selection must be confirmed against the partial pressure of the specific process stream.
Pressure vessels: shells, heads and nozzle pipework with design temperatures up to about 550 °C under GB 150.2. Welding procedure qualification is performed to NB/T 47014, and impact testing becomes a specified requirement at greater wall thicknesses.
Engineering machinery: hydraulic support tubes to GB/T 17396 and high-pressure cylinder barrels for construction equipment, where cold drawing delivers the dimensional accuracy required for honed bores.
Nuclear auxiliary systems: secondary and tertiary circuits such as water supply lines at moderate temperature; the primary steam path of the nuclear island uses austenitic stainless grades instead.
Selection and Processing Guidance
Wall thickness is normally selected from the design pressure and temperature using the allowable stress tables of the applicable code, with a corrosion allowance added for wet or sulphidic service. Because the grade is alloy steel rather than carbon steel, preheat and interpass temperature control are essential: the material is normally welded in the range 150-250 °C preheat with matching low-hydrogen filler, and post-weld heat treatment is applied to relieve residual stress in thick sections. Machining is straightforward in the normalised and tempered condition, and cold drawing is used to reach close tolerances for hydraulic and instrumentation duties.
Inspection and Common Pitfalls
Typical quality plans cover chemical verification by spectrographic analysis, tensile and impact testing, hydrostatic testing, eddy current or ultrasonic testing of the seamless body, and dimensional checks on ovality and wall eccentricity. Two mistakes appear repeatedly in service: using a low-temperature impact requirement on a grade that is not qualified below -20 °C, and treating 15CrMo as interchangeable with higher-chromium grades without re-qualifying the welding procedure. Both cases lead to either brittle fracture risk or unexpected creep damage.
FAQ
Q: What is 15CrMo steel pipe used for in power plants?
It is used for superheaters, reheaters, steam headers and main steam lines in subcritical boiler units, typically at metal temperatures of 450-540 °C and pressures up to about 14 MPa.
Q: Is 15CrMo equivalent to ASTM A335 P12?
Both grades belong to the 1Cr-0.5Mo family and show comparable elevated-temperature behaviour, but they are not identical documents. Substitution requires comparison of chemistry ranges, tensile requirements and creep data before it is accepted by the purchaser.
Q: Can 15CrMo pipe be used at low temperature?
No. The grade is designed for elevated-temperature service and is not qualified below -20 °C; low-temperature lines need a different material with verified impact toughness.
Q: What welding consumables are used for 15CrMo pipe?
Matching low-hydrogen filler metal of the 1Cr-0.5Mo class is used, with preheat of roughly 150-250 °C and post-weld heat treatment for thicker walls, all supported by a procedure qualification to NB/T 47014 or an equivalent code.
Q: What should be checked before hydrogen service?
The hydrogen partial pressure and temperature must be plotted against the Nelson curve of API 941, and where hydrogen sulphide is present the hardness and chemistry limits of NACE MR0175 also apply.
Q: How is 15CrMo pipe supplied?
It is delivered as hot-rolled or cold-drawn seamless pipe in the normalised and tempered condition, with mill test certificates covering chemistry, tensile properties and impact results, plus non-destructive testing when specified.
