How much is too much and how do you know it’s there?
For the vast majority of pumps manufactured around the world, the answer to the first part of that question is easy as the manufacturer will tell you that there should be no stresses imposed on the pump flanges by the system piping. The only difference are those pumps designed to A.P.I. (American petroleum Institute) Standards which are supposed to withstand specified levels of Moments of Forces on their pump flanges. However, in the real world, force from a variety of equipment is used to bring the pipe flanges sufficiently into line with the pump flanges, that the bolts can be slipped through the holes in both.
Rule of Thumb
Let me offer you a rule of thumb that has proved effective for many years and with all pipe sizes. If you can personally push the pipe into place (no outside equipment other than your own strength) to where the two flanges are in full face contact and aligned, then the pump casing can usually handle the stress, and there shouldn’t be a problem. If you can’t do that, the stress on the pump casing will be excessive and will result in frequent and regular seal and bearing failure. In case you’re not sure if there is any pipe stress being imposed on the pump flanges, complete the installation, conduct an accurate shaft alignment, then break the flange connections to the piping. If your shaft alignment changes, you have a problem. If not, the pump casing is free of pipe stress.
Ross Mackay is an internationally renowned expert in pumping reliability based in Canada. He specializes in helping companies increase their pump asset reliability and reduce operating and maintenance costs through pump training programs. He is the author of “The Practical Pumping Handbook”, and “The Mackay Self-Directed Pump Reliability Training System”. For more information and to register to possibly attend a Dynapumps and Ross Mackay pump school in 2013 please click here.