Seamless steel pipe selection principles and methods

(1) Preferred pipe materials
When selecting steel pipe materials, metal materials are generally considered first. When metal materials are not suitable, non-metal materials are then considered. For metal materials, steel pipes are preferred, and non-ferrous metal materials are considered later. Among steel pipes, carbon steel is first considered, and stainless steel is used when it is not suitable. When considering carbon steel materials, consider welded steel pipes first, and then choose seamless steel pipes when not applicable.
(2) Influence of medium pressure
The higher the pressure of the conveyed medium, the thicker the wall thickness of the steel pipe, and generally the higher the requirements for steel pipe materials. When the medium pressure is above 1.6MPa, seamless steel pipes or non-ferrous metal steel pipes can be used. When the pressure is very high, such as in the production of synthetic ammonia, urea, and methanol, the medium pressure of some steel pipes is as high as 32MPa. High-pressure seamless steel pipes made of 20# or 15CrMo are generally used. Steel pipes on vacuum equipment and oxygen steel pipes when the pressure is greater than 10MPa generally use copper tubes and brass tubes. When the medium pressure is below 1.6MPa, welded steel pipes, cast iron pipes or non-metallic steel pipes can be considered. However, the pressure of the medium that the cast iron steel pipe withstands shall not be greater than 1.0MPa. The medium pressure that non-metallic steel pipes can withstand is related to the type of non-metallic materials. For example, in rigid polyvinyl chloride steel pipes, the operating pressure is less than or equal to 1.6MPa; in reinforced polypropylene steel pipes, the operating pressure is less than or equal to 1.0MPa; in ABS steel pipes, the operating pressure Less than or equal to 0.6MPa. For water pipes, when the water pressure is below 1.0MPa, welded steel pipes made of Q235A are usually used; when the water pressure is greater than 2.5MPa, 20# seamless steel pipes are generally used.
(3) Influence of medium temperature
Steel pipes of different materials are suitable for different temperature ranges. For hydrogen with a pressure of 1.0MPa, when the hydrogen temperature is less than 350°C, 20# seamless steel pipes are generally used. When the hydrogen temperature is in the range of 351~400°C, 15CrMo or 12CrMo seamless steel pipes are generally used.
(4) Influence of chemical properties of the medium
To transport different media, different pipe materials are used. Some media are neutral and generally do not have high material requirements, so ordinary carbon steel pipes can be used; some media are acidic or alkaline, so acid- or alkali-resistant pipes must be selected. Strong acid and strong alkali and weak acid and weak alkali have different requirements for the use of steel pipes. The same acid or alkali has different material requirements for steel pipes with different concentrations. For transporting water and steam, steel pipes made of carbon steel can be used. For example, in a urea plant, stainless steel pipes are generally used to transport carbon dioxide, because carbon dioxide forms carbonic acid when it meets water, and carbonic acid has a corrosive effect on ordinary steel pipes. For example, carbon steel pipes can be used for fuming sulfuric acid, but carbon steel pipes cannot be used for dilute sulfuric acid, because dilute sulfuric acid and carbon steel can react chemically and corrode carbon steel, so duralumin pipes can be used.
(5) The influence of the function of the steel pipe itself
In addition to the function of transporting media, some steel pipes also have the function of absorbing shock, coefficient of thermal expansion and contraction, and the function of being able to move frequently under working conditions, such as civil liquefied petroleum gas, oxygen, and acetylene gas when filling bottles. For parts of the steel pipe, high-pressure steel wire braided hose is often used instead of hard steel pipe that is inconvenient to move.
(6) Effect of pressure drop
After the material of the steel pipe is initially selected, the pressure drop of the pipeline must be calculated to determine the inner diameter of the steel pipe. Through the calculation of pressure drop, see whether the selected materials meet the requirements. Especially when initially selecting plastic steel pipes, more attention should be paid to the review of pressure drop. The calculation of pressure pipelines in engineering design generally requires material balance, energy balance, and equipment calculation based on the production scale to initially determine the material flow rate. Refer to relevant information, assume a material flow rate, calculate the inner diameter of the steel pipe, check the manual or standards, and select a standard steel pipe. The inner diameter of the standard steel pipe usually selected should be equal to or slightly larger than the calculated inner diameter of the steel pipe. Then calculate the pressure drop in the pipe.