How is the maximum allowable working pressure of a centrifugal pump established?
The maximum allowable working pressure (MAWP) of a centrifugal pump begins with the required pressure of the pump’s application. It is then increased to match the MAWP of the next highest standard flange rating. It is common practice on standardized pump product designs to match pump working pressure with a standard flange rating so that the pump will be able to withstand hydrostatic pressure tests of the entire system. On engineered –to-order pumps, where this is impractical, then the MAWP is derived to match the application limits considering all potential variances in operating factors such as changes in speed, product density, etc.
The design of the pump casing and other pressure containing parts then follows the guidelines established by the appropriate design code (American Standard “ASME Code for Pressure Vessel Design, Section VIII” being one example). Such design codes include acceptable stress levels for materials of construction commonly used in pressure vessel construction.
Determination of metal thickness for pump casings and covers is not a simple matter because of the complex shape of pump volutes. For this reason finite element analysis methods are usually used. After that is done, additional metal thickness is added to allow for subsequent corrosion and erosion of the internal surface of the pump. For example, standard pumps designed for chemical applications usually have a corrosion allowance of one-eighth inch added.