Generally, according to the different uses and working conditions of steel pipe, different technical conditions should be proposed for the allowable deviation of steel pipe size, surface quality, chemical composition, mechanical properties, technological properties and other special properties.
When seamless steel pipes are used to transport water, gas, oil and other fluids and to manufacture various structural parts, sampling tests should be made on their mechanical properties such as tensile strength, yield strength and elongation. Conveyor steel pipes generally work under pressure conditions, and also require hydraulic test and technological performance tests such as flattening, flanging, etc. For large-scale long-distance crude oil, refined oil and natural gas pipelines, the requirements of carbon equivalent, weldability, low temperature impact toughness, stress corrosion under severe corrosion conditions, corrosion fatigue and strength under corrosive environment are increased.
Ordinary boiler steel pipes are used to manufacture superheated steam pipes and boiling pipes for boilers of various structures; high pressure boiler steel pipes are used for superheated steam pipes, heat exchangers and pipes for high-pressure equipment. The steel pipes for the above thermal equipment work under different conditions of high temperature and high pressure, and good surface condition, mechanical properties and technological properties should be guaranteed. Generally, its mechanical properties should be tested, flattening and hydraulic tests should be done, and the high-pressure boiler pipes should also be inspected for grain size and non-destructive testing should be more stringent.
Mechanical seamless steel pipe should have high dimensional accuracy, good mechanical properties and surface condition according to its application requirements. For example, bearing steel pipe requires high wear resistance, uniform structure and strict tolerance of internal and external diameters. In addition to the general mechanical properties test items, low-power, fracture, annealing structure (spheroidized, reticulated, banded), non-metallic inclusions (oxides, sulphides, dots, etc.), decarbonized layer and its hardness index are also tested.
High-pressure seamless steel pipes used in chemical fertilizer industry usually transport chemical media (such as synthetic ammonia, methanol, urea, etc.) under pressure of 2200-3200 MPa, working temperature of -0-400 C and corrosive environment. Therefore, besides high-pressure resistance, they should also 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 carried out according to different steel grades.
Steel pipes for petroleum and geological drilling work in harsh environments of high pressure, alternating stress and corrosiveness, so they should have high strength level, and have anti-wear, anti-torsion and anti-corrosion properties. The tensile strength, yield strength, elongation, impact toughness and hardness should be tested according to different grades of steel. For the casing, tubing and drill steel pipe used in oil wells, the steel grades and categories are divided in detail, and the additional technical conditions suitable for different environments and geological conditions are selected by users themselves to meet different special needs.
All kinds of stainless heat and acid resistant pipes used in chemical, petroleum cracking, aviation and other mechanical industries should be specially tested for intergranular corrosion, flattening, expanding and non-destructive testing in addition to mechanical properties and hydraulic pressure tests.