Pumps API 674 and API 675

DRG conducts pulsation studies according to API 674 or for metering pumps according to API 675.

The analysis method in Annex E of API 675 being comparable to that in API 674 Annex C.
Two analysis methods are detailed in Annex C.1.1. for pulsation and vibration control for reciprocating pumps; namely Design Approach 1 and Design Approach 2. For both of these use is made of our commercially available software BOSpulse for the acoustical simulation.
The choice between DA1 and DA2 depends on the complexity of the piping and the power of the pump.

 

Design Approach 1 (DA1)

Step 1) Here an acoustical model of the pump skid including the pump and the dampeners will be made to check for conformance with API 674 C.1.5 to C.1.7. The pulsation amplitudes downstream of the discharge dampener and upstream of the suction dampener are analysed for conformance with API674. The margins to the system relief pressure and liquid vapour pressure are also checked.

Step 2) The acoustical resonance frequencies of the piping are determined and it is checked that there is sufficient margin from the pump excitation frequencies (API 674 C.1.8).

Step 3) Separation from the mechanical resonance frequencies is then evaluated using span tables (API 688 (2012) 3.2).

 

Design Approach 2 (DA2)

This approach is more detailed than Design Approach 1, the two most important differences are:

  • The off-skid suction and discharge piping is included explicitly.
  • The forced response (acoustical and mechanical) is checked explicitly rather than separation margins.

Step 1) Acoustical analysis: Here an acoustical model of the entire system including the suction and discharge piping will be made to show conformance with API 674 C.1.5 to C.1.7. The pulsation amplitudes downstream of the discharge dampener and upstream of the suction dampener are analysed for conformance with API674. The margins to the system relief pressure and liquid vapour pressure are also checked.

Step 2) Static Stress Analysis: If required a piping flexibility study can be done for the piping design (often this will be performed by another party prior to the pulsation study). This analysis will ensure that the loads on the equipments and flanges are within acceptable limits for static loads.

Step 3) Mechanical Analysis: Here two approaches are possible depending on the pump and the preference of the client.

  • The piping is subject to a shaking force due to the fluctuating difference in pressure caused by a pulsation between an elbow pair. To ensure that large shaking forces do not overlap with a mechanical resonance mode, separation between the mechanical and acoustical resonance frequencies is checked according to API 674 C.1.8 using span tables (API 688 (2012) 3.2).
  • A forced mechanical response, where the response of the system to the shaking forces is calculated, is used to show conformance with API 674 C.1.8. In this method the stresses and displacements arising due to the excitation of mechanical resonance modes are assessed directly.