Force on a restriction plate in a pipe

[Spainers87]

Hi All,

We need to test a newly installed water distribution main. It is cement lined ductile iron (500mm). There are some issues with the mortar lining coming away from the pipe. The pipe hasn't been commissioned yet but we expect flows of 400-500l/s.

We are worred about further deterioration and damage to the large PRV downstream.

We need to test a seciton of the pipe to see the effect on the mortar of design flows. We can get flows of 100 l/s for testing so would need to create a blockage of approx 80% to have a flow velocity broadly equivalent to 500 l/s.

Unsure yet how to create the blockage but to do that I would like to estimate the force experienced by the blockage under the flows indicated.

Any ideas? Thank you in advance.

 

[itdepends]

You can't do this easily. The impact of that volumetric flow rate on the pipe wall is a function of the pipe geometry. Essentially for the same average velocity, the velocity of the fluid at the pipe wall decreases as the pipe diameter increases. That's why you get more pressure drop through 100m of 50mm pipe running at 2.5m/s than you do for 100m of 300mm pipe running at 2.5m/s.

In addition if you're already observing mortar coming away from the wall that will create eddy currents at those locations that will accelerate further damage.

If you put a restriction in the pipe work to create a locallised high velocity you will also create eddies that will give a higher erosion rate.

Worst case- test a section of pipe with water running down an incline until you get the velocity you need. But to be honest- if you see a response from this (or any other short term test) test - then you're pipeline is going to fail very quickly.

As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"

 

[LittleInch]

Why not insert a pipe of 80% internal area into your concrete lined pipe held up by some thin spider type arrangement equal to the length of your test section or at least 10 m or so? You would need to secure it fairly well and have a pointy nose cone, but would generate your equivalent velocity in the main part of the test section.

However I would have thought that a sectional pull off test would be easier to establish adhesion.

What does the manufacturer say??

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[bimr]

The first thing to do is to contact the manufacturer.

It is not possible to increase the velocity using just a lower flowrate. Q=VA. The only method to accomplish this is to install a smaller diameter pipe internal to the larger pipe.

It would be easier to set up a test rig consisting of a tank (5 min storage capacity), pump, and a pipe section to test.

The force would be simply pressure (in psi) times the area.

 

[Spainers87]

Thank you for your reply.

The loose liningwas apparently caused by damage in transit.

We will be doing sectional pull off tests but were looking to see how significant the damage is or if it is very localized.

We are planning to proceed with a swab in the pipe and pump water against it (essentially like the above suggestions). The swab could be moved along the pipe to provide an assessment (of some sort anyway) along the section.

Still concerned about the possible forces of 100l/s in a 500mm pipe against the swab and the securing lines.

Don't think I've ever heard of this done before so is potentially quite exciting.