Technical Specifications for Pipeline Material Design

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Technical Specifications for Pipeline Material Design 1 General Provisions These specifications apply to the pipeline materials used in various installations in engineering projects. They outline the general design requirements for pipeline materials. Designers involved in the selection of pipeline materials for a project can make necessary adjustments to these specifications based on the specific characteristics of that project, through consultation with the project manager, to ensure proper implementation in each project. 2 Selection of Design Temperature and Design Pressure for Pipelines General Provisions 2.1 The design temperature of a pipeline should be determined as the highest temperature that the fluid passing through it may reach under the most severe conditions of combined pressure and temperature. Specifically: a) For pipelines without pressure relief devices or those isolated from such devices, the design pressure should not be lower than the maximum pressure that the fluid can reach. b) For pipelines equipped with pressure relief devices, the design pressure should not be less than the opening pressure of those devices. c) The design pressure of the outlet pipeline of a centrifugal pump should not be less than the sum of the suction pressure and the pressure corresponding to the pump’s head. d) The design pressure of the outlet pipeline of a reciprocating pump is set at the setting value of the pump’s safety valve. e) The design pressure of the outlet pipeline of a compressor is equal to the compressor’s outlet pressure. f) Negative-pressure pipelines should be designed to withstand external pressures; when equipped with safety control devices, the design pressure is taken as 1.25 times the maximum difference between internal and external pressures, or 0.1 MPa, whichever is lower. In the absence of such control devices, the design pressure is 0.1 MPa. For jacketed vacuum pipes where there is internal pressure inside the jacket, the design pressure is the sum of the design pressure of a vacuum pipe without a jacket and the internal pressure within the jacket. However, it is necessary to verify the stability of the external pressure under the test pressure applied to the jacket. For jacketed pipes with a vacuum inside the jacket, the design pressure is the design pressure of a pipe under internal pressure plus 0.1 MPa, again with a check on the stability of the external pressure under the jacket’s test pressure. g) For pipelines carrying fluids such as refrigerants or liquefied hydrocarbons, which have low boiling points, the design pressure should not be less than the highest pressure that can occur due to vaporization at the highest ambient temperature when the valve is closed or when the fluid is not flowing. h) It is not permissible for the pressure and temperature in non-metallic pipelines to exceed the design values due to changes in either or both of these factors. The design conditions should be determined based on the most severe conditions of combined pressure and temperature. 2.2 The design pressure of a pipeline should be selected to be no less than the highest pressure that may occur under the combined effects of internal and external pressures and temperature during operation. Specifically: a) The design temperature of a material should not exceed the highest temperature allowed for that metal or non-metallic material. For pipelines operating at temperatures below 0, the material temperature should not be lower than the lowest temperature that the material can tolerate. b) The design temperature for non-metallic materials is generally taken as the temperature of the fluid. If the ambient temperature in the installation area exceeds this design temperature, then the ambient temperature shall be used as the design temperature. c) For uninsulated pipelines, when the operating temperature of the fluid is less than 65, the operating temperature of the fluid is used as the design temperature. When the operating temperature of the fluid is greater than 65, unless the wall temperature is determined through heat transfer calculations, the design temperature for the pipeline components should not be lower than one of the following values: 1) For valves, welded pipe fittings, and pipeline components with wall thicknesses similar to those of the pipes, 0.95 times the temperature of the fluid inside the pipe can be used as the design temperature. 2) For valves and flanges connected by flanges (excluding loose-flange fittings), 0.9 times the temperature of the fluid inside the pipe can be used as the design temperature