1 Single-phase flow (incompressible fluid)
1.1 Brief description
1.1.1 This specification is applicable to the calculation of flow pressure drop of Newtonian single-phase fluid in pipeline. The system is subjected to hydraulic calculation when the working pressure of all relevant main equipment has been basically determined by the chemical process specialty. The pressure drop of pipelines (including pipes, valves, control valves, flowmeters and pipe fittings, etc.) between major equipment shall be calculated according to the requirements of chemical process, so as to control the total pressure drop of the system within a given range of working pressure. On this basis, such items are determined, i.e. pipeline size, equipment nozzle size, allowable pressure drop of control valves and flowmeters, relief pressure of safety valves and blasting pieces, etc.
1.1.2 Newtonian fluid is a fluid whose shear stress is proportional to the velocity gradient and whose proportionality coefficient is viscosity. All gases are Newtonian fluids. Except liquids and mud composed of polymers and other substances, most liquids are also Newtonian fluids.
1.2 Calculation methods
1.2.1 Precautions
1.2.1.1 Safety factor
Since the safety factor is not considered in the calculation method, a reasonable value shall be selected according to the actual situation. In general, for the steel pipes that will be used 5 to 10 years in average, the friction coefficient plus a safety factor of 20% to 30% may adapt to the changes in roughness conditions; for steel pipes used more than 5 to 10 years, the conditions tend to remain stable, but may further deteriorate. The increased pressure drop due to the flow increase is not considered in this coefficient, so an additional safety factor of 10% to 20% is required. In this specification, the friction pressure drop of the system is determined by the value of the calculated friction pressure drop multiplied by 1.15, but the static pressure drop and other pressure drops are not multiplied by a coefficient.
1.2.1.2 Accuracy of calculation
In engineering calculation, it is suitable to reserve the two significant figures after decimal places as the calculation result. In all calculations of pressure drop calculated by equivalent length, the significant figures in the final result shall not exceed two decimal places.
1.2.2 Pipe diameter
1.2.2.1 General principle for determining pipe diameter
(1) The pipe diameter shall be determined according to the design conditions, and where necessary, a margin of 15% to 25% of the pressure drop under the design conditions may be provided, except in the following cases:
a. A certain circulation volume shall be considered for the size of outlet pipe in the piping system with fuel oil circulation;
b. The pipeline size of pumps, compressors and blowers shall be determined according to the maximum process flow (under the designed allowable flow velocity of the equipment), instead of the maximum capacity of the machine;
c. The size of pipeline used intermittently (e.g. bypass pipeline during construction) shall be determined according to the possible pressure difference.
(2) Within the allowable pressure drop range, economic pipe diameter shall be adopted. See Table 1.2.2-1 for the allowable pressure drop range of fluid in some pipelines.
(3) For some fluids that will corrode and abrade the pipe wall, the pipe diameter is determined by the flow velocity, which is shown in Table 1.2.2-2.
1.2.2.2 Calculation of pipe diameter
The following equation applies:
