Dear sir,
We are operating cross country LPG pipeline. At dispatch terminal we are receiving LPG from refinery. For boosting pressure of LPG we have multistage centrifugal pumps. As per OEM specification of pumps density of LPG shall be in range of 0.515-0.585 ]MT/m3(OEM). Now supplier has commissioned another refinery and started supply of LPG from there. LPG of new plant is of low density in range of 0.500 -0.510 MT/m3, which is less than OEM specs. So we are denying as per OEM specification. Supplier is forcing us to take this LPG on basis of Indian standard IS-4576 which he is fulfilling. In this standard nothing is given about density of LPG. But vapour pressure that shall in between 500kpa to 1050kpa.(i.e. any mixture of propane and butane can be possible.), other parameters he is fulfilling.
As per our understanding following may be consequences of operating pump with low density:
(1) NPSH related problem, because of high vapour pressure LPG , but pressure available is 20 Kg/cm2 at suction so this possibility is rare.
(2) Metal to metal contact at close clearance parts inside pump.
(3) Mechanical seal related problem.(mechanical seal, dual type API plan 11 & 52)
Is viscosity will be less of low density LPG, which may lead pure lubrication in side pump and mechanical seal faces?

[U]In summary: What will be adverse effect on pump if we operate it with lower density LPG than OEM recommended(0.515-0.585 MT/m3)?[/U]

Thanking you for consideration and time.
Regards
Parbat Singh
Sr Engineers

When the specifications are set by manufacturer the warranty for same becomes null and void if not met.
Then your company would be responsible for cost of replacing parts or pumps
Would the supplier be willing to assume the cost of replacement of failed equipment due to the lower LPG they supply?
Perhaps providing them with the cost of replacement of equipment would be a start toward solving your situation.
At worst -If this problem would lead to a bad situation/incident, having the supplier as a co-insurer of same would be best.