1 reply to this topic

[Abdelilah]

Hi dear all,

 

I've query about pump Maximum Allowable Working Pressure calculation.

 

Currently we would purchases condensate pump. The bidder suggest the following :

 

-- This requirement (i.e. maximum discharge pressure to include maximum diameter impeller) will increase / impact following:

 

1 .Pump shut off Pressure

2. Downstream design pressure.

3. Pump MAWP

4. Motor rating / sizing

 

However modification / ammendment  to clause no 6.3.2 (i.e. requirement of Max. discharge pressure to include max. impeller diameter, sp. Gravity & trip speed) of API610,11^th Edition in Mechanical Specification for Centrifugal Pumps is not done / considered.

 

Based on above & to avoid over sizing of the equipments / connected piping, Bidder has considered Pump MAWP is considered based on maximum discharge pressure and max. specific gravity at rated impeller diameter ----

 

 

However, I've found in the literature that this pressure calculation is based upon :

 

The maximum allowable working pressure (MAWP) shall be based on the maximum specified relative density with:

• Maximum impeller diameter at rated speed for constant speed applications.
• Rated impeller diameter at maximum speed for variable speed applications.

 

We Would appreciate if some one explain to us what the above means please !

 

Best Regards.

A.Baghdadi

[Technical Bard]

The MAWP of the pump should be set based on the maximum impeller to ensure that in future, if the impeller is changed, that the larger impeller cannot overpressure the pump and downstream piping.  There are numerous examples of this having not been done and failures occurring.

 

The allowance for using the rated (delivered) impeller for variable speed pumps but at maximum speed can be done, but that can still have risk that the impeller is changed later and a failure occurs.

 

If you change the impeller later, you don't want to have to change the piping (and even the whole pump casing) just to get a little more flow.