A pressure pipe is a tubular device used to transport gas or liquid under a certain pressure. Its scope is stipulated as the gas, liquefied gas, steam medium with the maximum working pressure greater than or equal to 0.1MPa, or the liquid medium with the highest working temperature higher than or equal to the standard boiling point, which is flammable, explosive, toxic or corrosive,and the pipe with nominal diameter greater than 25mm.
Principles for selection of commonly used steel pipe materials for pressure pipelines
1. Preferred pipe material
When selecting pipe materials, metal materials are generally considered first, and non-metal materials are considered when metal materials are not applicable. Steel pipes are preferred for metal materials, and non-ferrous metal materials are considered later. Among steel pipes, carbon steel pipes should be considered first, and stainless steel pipes should be used when it is not applicable. When considering carbon steel materials, consider welded steel pipes first, and then choose seamless steel pipes when they are not applicable.
2. Effect of medium pressure
(1) The higher the pressure of the conveying medium, the thicker the wall thickness of the pipe, and the higher the requirements for the pipe material.
(2) When the medium pressure is above 1.6MPa, seamless steel pipes or non-ferrous metal pipes can be used. When the pressure is very high, the high-pressure seamless steel pipe made of 15CrMo is generally selected. The tubes on the vacuum equipment and the oxygen tubes when the pressure is greater than 10MPa generally use copper tubes and brass tubes.
(3) When the medium pressure is below 1.6MPa, welded steel pipes, cast iron pipes or non-metallic pipes can be considered. However, the pressure of the cast iron pipe to withstand the medium shall not exceed 1.0MPa.
3. Effect of medium temperature
Tubes of different materials are suitable for different temperature ranges. For hydrogen with a pressure of 1.0MPa, when the temperature of hydrogen is less than 350°C, 20# seamless steel pipes are generally used. When the temperature of hydrogen is in the range of 351~400°C, 15CrMo or 12CrMo seamless steel pipes are generally used.
4. Effect of medium chemical properties
Different media are transported, and different pipe materials are used. Some media are neutral, and generally do not have high requirements for materials, and ordinary carbon steel pipes can be used; some media are acidic or alkaline, so acid-resistant or alkali-resistant pipes must be selected. Strong acids and strong bases and weak acids and weak bases have different requirements for the use of pipes. The same acid or alkali has different requirements for pipe materials with different concentrations.
5. The influence of the function of the tube itself
In addition to the function of conveying medium, some pipes also have the function of shock absorption and the function of thermal expansion and contraction. Under working conditions, for functions that can be moved frequently, such as civil liquefied petroleum gas, oxygen, and acetylene gas in the bottle filling position, the pipes often use high-pressure steel wire braided rubber hoses instead of hard steel pipes that are inconvenient to move.
6. Effect of pressure drop
(1) After the material of the pipe is initially selected, the pressure drop of the pipe must be calculated to determine the inner diameter of the pipe. Through the calculation of the pressure drop, see whether the selected materials meet the requirements. Especially when plastic pipes are initially selected, more attention should be paid to the review of pressure drop.
(2) Calculation of pressure pipelines. In engineering design, material balance calculation, energy balance calculation and equipment calculation are generally carried out according to the production scale, and the material flow rate is initially determined. And refer to the relevant information, assuming a material flow rate, calculate the inner diameter of the pipe, check the manual or standard, select the standard pipe, usually the inner diameter of the standard pipe selected should be equal to or slightly larger than the calculated inner diameter of the pipe. Then calculate the pressure drop in the pipe.
Summarize
When designing pressure piping, after the pipe diameter is calculated and determined, the material of the pipe must be selected. The use of commonly used pipe materials for pressure pipes is determined according to the operating conditions of the conveyed medium (such as pressure, temperature) and its medium characteristics under these conditions. Improper selection of materials will cause waste or bury hidden dangers of accidents.
Principles for selection of commonly used steel pipe materials for pressure pipelines
1. Preferred pipe material
When selecting pipe materials, metal materials are generally considered first, and non-metal materials are considered when metal materials are not applicable. Steel pipes are preferred for metal materials, and non-ferrous metal materials are considered later. Among steel pipes, carbon steel pipes should be considered first, and stainless steel pipes should be used when it is not applicable. When considering carbon steel materials, consider welded steel pipes first, and then choose seamless steel pipes when they are not applicable.
2. Effect of medium pressure
(1) The higher the pressure of the conveying medium, the thicker the wall thickness of the pipe, and the higher the requirements for the pipe material.
(2) When the medium pressure is above 1.6MPa, seamless steel pipes or non-ferrous metal pipes can be used. When the pressure is very high, the high-pressure seamless steel pipe made of 15CrMo is generally selected. The tubes on the vacuum equipment and the oxygen tubes when the pressure is greater than 10MPa generally use copper tubes and brass tubes.
(3) When the medium pressure is below 1.6MPa, welded steel pipes, cast iron pipes or non-metallic pipes can be considered. However, the pressure of the cast iron pipe to withstand the medium shall not exceed 1.0MPa.
3. Effect of medium temperature
Tubes of different materials are suitable for different temperature ranges. For hydrogen with a pressure of 1.0MPa, when the temperature of hydrogen is less than 350°C, 20# seamless steel pipes are generally used. When the temperature of hydrogen is in the range of 351~400°C, 15CrMo or 12CrMo seamless steel pipes are generally used.
4. Effect of medium chemical properties
Different media are transported, and different pipe materials are used. Some media are neutral, and generally do not have high requirements for materials, and ordinary carbon steel pipes can be used; some media are acidic or alkaline, so acid-resistant or alkali-resistant pipes must be selected. Strong acids and strong bases and weak acids and weak bases have different requirements for the use of pipes. The same acid or alkali has different requirements for pipe materials with different concentrations.
5. The influence of the function of the tube itself
In addition to the function of conveying medium, some pipes also have the function of shock absorption and the function of thermal expansion and contraction. Under working conditions, for functions that can be moved frequently, such as civil liquefied petroleum gas, oxygen, and acetylene gas in the bottle filling position, the pipes often use high-pressure steel wire braided rubber hoses instead of hard steel pipes that are inconvenient to move.
6. Effect of pressure drop
(1) After the material of the pipe is initially selected, the pressure drop of the pipe must be calculated to determine the inner diameter of the pipe. Through the calculation of the pressure drop, see whether the selected materials meet the requirements. Especially when plastic pipes are initially selected, more attention should be paid to the review of pressure drop.
(2) Calculation of pressure pipelines. In engineering design, material balance calculation, energy balance calculation and equipment calculation are generally carried out according to the production scale, and the material flow rate is initially determined. And refer to the relevant information, assuming a material flow rate, calculate the inner diameter of the pipe, check the manual or standard, select the standard pipe, usually the inner diameter of the standard pipe selected should be equal to or slightly larger than the calculated inner diameter of the pipe. Then calculate the pressure drop in the pipe.
Summarize
When designing pressure piping, after the pipe diameter is calculated and determined, the material of the pipe must be selected. The use of commonly used pipe materials for pressure pipes is determined according to the operating conditions of the conveyed medium (such as pressure, temperature) and its medium characteristics under these conditions. Improper selection of materials will cause waste or bury hidden dangers of accidents.
