Technical conditions of seamless steel pipes for different purposes

Generally, according to the different purposes and working conditions of seamless steel pipes, different technical conditions should be proposed for the allowable deviation of steel pipe size, surface quality, chemical composition, mechanical properties, process performance and other special properties.

When general seamless steel pipes are used to transport water, gas, oil and other fluid pipes and to manufacture various structural parts, sampling tests should be done on their mechanical properties such as tensile strength, yield strength and elongation. The conveying pipe generally works under pressure, and it is also required to do water pressure test and process performance tests such as flaring, flattening, and crimping. For large-scale long-distance crude oil, refined oil, and natural gas pipelines, the requirements for carbon equivalent, welding performance, low-temperature impact toughness, stress corrosion under severe corrosive conditions, corrosion fatigue and strength under corrosive environments have been increased.

Ordinary seamless boiler tubes are used to make superheated steam tubes and boiling water tubes for boilers of various structures; high-pressure boiler tubes are used for superheated steam tubes, heat exchangers and pipelines for high-pressure equipment in high-pressure or ultra-high-pressure boilers. The above-mentioned steel pipes for thermal equipment are all working under different conditions of high temperature and high pressure, and good surface condition, mechanical properties and process performance should be ensured. Generally, the mechanical properties are inspected, flattening and water pressure tests are done, and the high-pressure boiler tube also requires the inspection of the grain size and more stringent non-destructive testing.

Seamless mechanical steel tube must have high dimensional accuracy, good mechanical properties and surface condition according to the requirements of the application. For example, the bearing tube requires high wear resistance, uniform organization and strict inner and outer diameter tolerances. In addition to general mechanical performance inspection items, low power, fracture, annealing structure (spheroidized structure, mesh, ribbon), non-metallic inclusions (oxide, sulfide, dots, etc.), decarburization Layer and its hardness index and other tests.

High-pressure seamless steel pipes for the chemical fertilizer industry often transport chemical media (such as synthetic ammonia, methanol, urea, etc.) in a pressure of 2200～3200MPa, working temperature of -0～400～C and corrosive environment. Therefore, in addition to high pressure resistance, they are also It should have strong corrosion resistance, good surface condition and mechanical properties. In addition to mechanical properties, flattening and hydrostatic tests, corresponding intergranular corrosion tests, grain size and more stringent non-destructive testing should be done according to different steel grades.

Petroleum and geological drilling steel pipes work in harsh environments of high pressure, alternating stress, and corrosiveness, so they should have a high level of strength, and have anti-wear, torsion and corrosion resistance properties. Tests for tensile strength, yield strength, elongation, impact toughness and hardness should be done according to different steel grades. For seamless tubing and seamless drill pipe used in oil wells, the steel grades, categories, and additional technical conditions that are suitable for different environments and geological conditions are selected by users and meet different requirements.

Various stainless, heat-resistant and acid-resistant pipes used in chemical, petroleum cracking, aviation and other mechanical industries are not only used for mechanical properties and hydraulic pressure tests, but also for intergranular corrosion tests, flattening, flaring, and non-destructive testing.