How to classify by alloy elements?
Alloy steel pipes can be divided into chromium-molybdenum steel (such as 15CrMo), nickel-based alloys (such as Inconel), manganese steel (such as 65Mn), etc. according to the main alloying elements. Chromium-molybdenum steel is known for its high temperature and high pressure resistance and is often used in power plant boilers; nickel-based alloys have strong corrosion resistance and are suitable for chemical and marine environments; manganese steel focuses on high wear resistance and is used in engineering machinery. Different categories correspond to different heat treatment processes, for example, chromium-molybdenum steel requires normalizing + tempering. Classification directly affects the price of steel pipes, and the cost of nickel-based alloys can be more than 10 times that of ordinary steel.
What are the differences between ASTM and ISO standards for alloy steel pipes?
ASTM standards (such as ASTM A335) focus more on high temperature performance and require clear creep rupture data; ISO 9329 focuses on the limit value control of chemical composition. For example, ASTM allows higher phosphorus and sulfur residues, while ISO has stricter requirements. During certification, ASTM needs to pass more mechanical property tests, while ISO emphasizes non-destructive testing coverage. When exporting, enterprises need to meet the dual standards of the target market at the same time, which increases production costs.
Special certification requirements for high-temperature alloy steel pipes?
Such steel pipes (such as P92) must pass ASME III or RCC-MRx nuclear power standard certification, including high-temperature endurance tests up to 10,000 hours. The material must provide a complete intergranular corrosion report and delta ferrite content detection. For example, the steel pipes for thermal power ultra-supercritical units require a strength of >100MPa at 650°C. In addition, manufacturers must have special qualifications such as NADCAP heat treatment, and the supply chain audit is extremely strict.
Advantages and applications of duplex stainless steel pipes?
Duplex steel (such as 2205) has both austenite and ferrite structures, and its chloride ion corrosion resistance is twice that of 304 stainless steel, and its strength is higher. Its yield strength can reach twice that of ordinary stainless steel, which is suitable for submarine pipelines or desulfurization equipment. However, welding requires controlling the heat input to avoid σ phase embrittlement. Although the cost is higher than 316L, the life cycle economy is better.
How to distinguish between seamless and welded alloy steel pipes?
Seamless pipes are produced by perforation and rolling, without welds, and have stronger pressure bearing capacity; welded pipes are produced by coiling steel plates (such as ERW process), and there is a heat-affected zone. Microscopic metallographic observation can reveal a sudden change in the grain flow direction of welded pipes. For example, oil cracking pipes must be produced by seamless technology, while welded pipes can be used for low-pressure fluid transportation. Seamless pipes account for more than 80% in the high-end field, but the cost of welded pipes is more than 30% lower.
