Introduction to Alloy Steel Pipe

What is alloy steel pipe?

Alloy steel pipe is made of carbon steel, alloy structural steel and stainless heat-resistant steel, and is made by hot rolling or cold rolling. It is mainly used in high-pressure and high-temperature environments such as power plants, nuclear power, high-pressure boilers, and high-temperature superheaters. It has 100% recyclability and plays an important role in the fields of oil, natural gas, chemical industry and machinery manufacturing.

The pipe adopts a hollow cross-section design, which has both lightweight and high strength characteristics, can save materials and optimize the manufacturing process, and is widely used in oil drill pipes, automobile transmission shafts, building scaffolding and military equipment. According to the cross-sectional shape, it can be divided into round tubes and special-shaped tubes, among which round tubes occupy the mainstream due to their uniform pressure resistance and high fluid delivery efficiency. The material grade is represented by a combination of element symbols and numbers. For example, 40Cr represents chromium alloy steel with an average carbon content of 0.4%, and 12Cr1MoV is marked with the content of elements such as chromium, molybdenum, and vanadium.

What is seamless alloy steel pipe?

Seamless alloy steel pipe is a weldless pipe made of alloy steel through hot rolling, cold rolling or cold drawing (integral forming, avoiding weak points at the weld, and stronger pressure bearing capacity). It has high strength, high temperature resistance, corrosion resistance and other characteristics, and is widely used in the transportation of high pressure, high temperature or corrosive media. The cold drawing process can produce high-precision and high-finish pipes.

What is welded alloy steel pipe?
Welded alloy steel pipe (alloy steel welded pipe) is a pipe made of alloy steel plate or steel strip by welding process (such as high frequency welding(HFW), submerged arc welding, etc.). It has the high strength, corrosion resistance or high temperature resistance of alloy steel. At the same time, it is lower in cost than seamless alloy pipe and is suitable for medium and high pressure, corrosive or high temperature environment.

Material of alloy steel pipe:
The main material of alloy pipe is alloy steel, that is, one or more alloy elements (such as chromium, nickel, molybdenum, vanadium, titanium, etc.) are added to carbon steel to improve its performance.

Common types of alloy pipes include:

1. Chromium-molybdenum alloy (Cr-Mo): such as 15CrMo, 12Cr1MoV, P91 (9Cr-1Mo-V), resistant to high temperature and high pressure, used for high temperature and high pressure pipelines of boilers and petroleum cracking units.
2. Nickel-based alloy: such as Inconel 600/625, resistant to strong acids and alkalis and high temperatures, used in chemical, aerospace and marine engineering.
3. Stainless steel alloys: such as 304, 316L, 2205 (S31803), which have both high strength and corrosion resistance, are often used in food, seawater treatment and chemical industries.
4. Low temperature alloys: such as 9Ni steel, used in liquefied natural gas (LNG) storage and transportation equipment.

Characteristics of alloy steel pipes:
1) High strength: more able to withstand high pressure, impact or heavy load than ordinary carbon steel pipes, suitable for harsh working conditions.
2) High temperature/low temperature resistance: such as chromium-molybdenum steel (Cr-Mo) pipes can work for a long time at high temperatures above 500°C (such as boiler tubes), and low temperature alloy pipes (such as nickel-based alloys) are suitable for liquefied natural gas (LNG) extremely cold environments.
3) Corrosion resistance: adding elements such as chromium and nickel can resist acid, alkali, salt or hydrogen sulfide corrosion, such as 316L stainless steel pipes for chemical equipment.

4) Good processability: can be welded and bent to meet complex process requirements.
5) High cost: due to complex alloy elements and processes.
6) Customized performance: By adjusting the alloy composition (such as adding molybdenum to increase hardness), specific needs (such as wear-resistant pipes) can be met.

Advantages of alloy steel pipes:
The biggest advantage of alloy steel pipes is that they can be 100% recycled, which is in line with the national strategy of environmental protection, energy saving and resource conservation. National policies encourage the expansion of the application field of high-pressure alloy pipes. China's alloy pipe consumption accounts for only half of the total steel volume in developed countries. The expansion of the use of alloy pipes provides a broader space for the development of the industry. According to the research of the expert group of the Alloy Pipe Branch of the China Special Steel Association, the demand for long high-pressure alloy pipes in China will increase by an average of 10-12% per year in the future. Alloy pipes are defined by steel pipes according to production materials (that is, materials). As the name suggests, they are pipes made of alloys; while seamless pipes are defined by steel pipes according to production processes (seamless or seam). The difference between seamless pipes and seamless pipes is seam pipes, including straight seam welded pipes and spiral pipes.

Manufacturing process of alloy steel pipes:
Hot rolling/cold rolling: forming through rolling process, cold rolling has higher precision.
Seamless process: using perforation, extrusion and other technologies to ensure no welds (commonly used in high-pressure scenarios).
Welding process: Steel plate coil welding, low cost, used in low-pressure environment.

Main application areas:
Oil and gas: transport oil, gas or high-temperature and high-pressure media, such as oil drilling pipelines, nuclear power heat exchange tubes.
Chemical equipment: acid and alkali corrosion-resistant pipeline systems, reactor linings.
Power industry: boiler superheater, reheater pipelines.
Mechanical manufacturing: high-strength hydraulic system, bearing sleeve.

Aerospace: engine components, fuel pipelines.

Mechanical properties:

Standard	Brand	Tensile strength (MPa)	Yield strength (MPa)	Elongation (%)	Hardness
GB3087	10	335～475	≥195	≥24	/
20	410～550	≥245	≥20	/
GB5310	20G	410～550	≥245	≥24	/
20MnG	≥415	≥240	≥22	/
25MnG	≥485	≥275	≥20	/
15CrMoG	440～640	≥235	≥21	/
12Cr2MoG	450～600	≥280	≥20	/
12Cr1MoVG	470～640	≥255	≥21	/
12Cr2MoWVTiB	540～735	≥345	≥18	/
10Cr9Mo1VNb	≥585	≥415	≥20	/
ASME SA210	SA210A-1	≥415	≥255	≥30	≤143HB
SA210C	≥485	≥275	≥30	≤179HB
ASME SA213	SA213 T11	≥415	≥205	≥30	≤163HB
SA213 T12	≥415	≥220	≥30	≤163HB
SA213 T22	≥415	≥205	≥30	≤163HB
SA213 T23	≥510	≥400	≥20	≤220HB
SA213 T91	≥585	≥415	≥20	≤250HB
SA213 T92	≥620	≥440	≥20	≤250HB
DIN17175	ST45.8/Ⅲ	410～530	≥255	≥21	/
	15Mo3	450～600	≥270	≥22
13CrMo44	440～590	≥290	≥22	/
10CrMo910	480～630	≥280	≥20	/

Alloy steel pipe specification table:

Why choose alloy pipes?
Alloy pipes are required when ordinary steel pipes cannot meet the following conditions:
Extreme temperature (high or low temperature)
Strong corrosive media (such as H₂S, hydrochloric acid)
Ultra-high pressure (such as oil and gas well casing)
Special wear-resistant requirements (such as mining slurry pipes)

How to choose seamless alloy pipes?
Clear purpose: Select the material according to temperature, pressure, and medium. For example, choose 316L for acid resistance, and choose sulfur-resistant pipes for H₂S corrosion environment.
Process requirements: Seamless pipes are preferred for high pressure environments, and welded pipes can be considered for low pressure environments.
Certification and testing: Check the warranty to ensure compliance with ASTM, GB, API and other standards, and conduct ultrasonic flaw detection and water pressure testing when necessary.

Alloy steel seamless pipe vs welded pipe: How to choose?

Alloy steel seamless pipe: 

Preferred for ultra-high pressure, small diameter (thick wall), high temperature, strong corrosion, high purity scenarios.

Alloy steel welded pipe: 

Suitable for medium and low pressure, large diameter (thin wall), low cost, fast delivery requirements.
In special cases: welded pipe + heat treatment (such as normalizing, quenching) can partially replace seamless pipe, but strict quality control is required.

Read more: Seamless alloy steel pipe vs. Seamless carbon steel pipe or ASTM A335 Alloy Steel Seamless Pipe