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Do I Need to Throw In a Few Feet of Head to Account for Pigging?

Do I Need to Throw In a Few Feet of Head to Account for Pigging?

Do I Need to Throw In a Few Feet of Head to Account for Pigging?

(OP)
Hi guys.  A question.  When sizing a pump that charges a pipeline that will be pigged, and if this charge pump is also used as the motive force to drive the pig during the pigging, do I need to throw in a few extra feet of TDH oomph to account for the friction of the pig against the pipe wall?

In other words, if my pump calc says I need 500' TDH, do I throw in 2% or some odd more to make sure I've covered my pokey during the pigging?

Thanks guys!  Pete

RE: Do I Need to Throw In a Few Feet of Head to Account for Pigging?

Try contacting a pigging operation vendor? I think they could tell you the normal dP as a function of size and flow rate for various types of pigs.

Best regrads

Morten

RE: Do I Need to Throw In a Few Feet of Head to Account for Pigging?

Normally you would not need to do that, as you would typically reduce your flowrate, bring the pumps back to a higher disch head, and thereby have enough head left over to move the lower flowrate and the pig too.  

Are you planning to pig at full design flowrate or something???  If you think you will do that, then ya, you might need to add some head at your BEP.   

Let your acquaintances be many, but your advisors one in a thousand'  ...  Book of Ecclesiasticus

RE: Do I Need to Throw In a Few Feet of Head to Account for Pigging?

One kind of force is pressure applied over an area.  If you have a 10-inch pig, the area is 78 in^2.  A 10" foam pig weighs 15 lbf.  If the friction resistance is 3 times the pig weight then you need to apply about 60 lbf which is less than ONE psid.  Now if you're pigging a gas line and have a load of liquid in front of the pig and gas behind you need to add some force to move the liquid, but you don't do that with a pump.  It sounds like you have a liquid line and are using a cleaning or batching pig, so the only force required is enough to move the pig.  You don't need to add head to the pump.

David

RE: Do I Need to Throw In a Few Feet of Head to Account for Pigging?

KernOily isn't going to be pigging a gas line, unless he's changed jobs.

You wouldn't need to add head to the pump, if you're prepared to accept what would usually be a lower flowrate.  Adding a pig increases resistance at least a little, so the pump will run back on the curve as it increases the discharge head in the attempt to find that little bit of extra head needed to move the pig.  That will also mean at least some tiny reduction of flow.  If you can live with whatever that lower flowrate is during the pigging operation, then you don't need to get a pump with a higher discharge head output curve.  That will almost always be the case, but it is conceivable that a pump already working at low capacity in the flat region of its curve might lose a considerable amount of flow with little to no increase in head if somebody dropped a pig, or a bunch of spheres in the line.  In that case you would need to get some more differential head from somewhere, most commonly by lowering the outlet pressure of your pipeline.  If you couldn't do that, another alternative might be to increase the pump's suction pressure.  If you couldn't do that, then the last alternative at that point would be to get a pump (or boost) to a higher discharge head.   

Let your acquaintances be many, but your advisors one in a thousand'  ...  Book of Ecclesiasticus

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