Pumps and the Expansion Joint

1. Really you are entering to adventurousness if you going to do this step maybe you will solve some things but you will defect another thing. I don't have experience in this field but the designer not install the expansion joint in the piping system futility. The expansion joint will reduce the piping expand or piping thermal growth if it's under high temperature. Your problem is piping vibration you can solve this by another way check your process either clam your piping or install a rubber under the place which is affected by vibration to dump the vibration otherwise if you remove the expansion joint may lead the piping to break and foundation destruction.

VCM Inspector wrote "The expansion joint will reduce the piping expand or piping thermal growth if it's under high temperature."

Well, that is not exactly correct. An Expansion Joint does not prevent the expansion of metal pipe due to high temperature. The pipe will still expand no matter what kind of compensation (Loop configuration, bellows joint or slip joint) you use.

Before you do any thing to modify the piping system you need to determine what is causing the vibration. It may be that the pump is experiencing cavitation because the liquid level in the source vessel is running low (below NPSHR) and the pump is starving. I have hands on experience with this situation. Everyone said my piping was wrong. I found out that there was a faulty Level Controller on the source vessel. We had them over-ride the LC and return the liquid level to the required level. Guess what? No more vibrations.

The primary purpose of an expansion joint at the pump's suction (at some cases at discharges) pipe connection is to accommodate the thermal expansion of the pipe line. Such that the expansion of the pipe line will not foul the pump's holding. Replacing this with an 'expansion loop' has to be carefully designed and supported.

Since expansion joints are of corrugated metal tubes or rubber hose, they may restrict the vibration from the pumps to get transferred to pipelines (also vice versa), but this is incidental.

We do not allow flexible expansion joints in our pipelines. They are a potential weak point that should be avoided if you are pumping any kind of hazardous substance (and even if you are not). They are (in most cases) not necessary if the pipework is properly designed and fabricated.

Neither the pipes nor the expansion joint should be expected to "absorb" vibration. Your pump should not be inducing any sort of meaningful vibration force, either mechanical or hydraulic, to the surrounding pipework.

Also, the pump should not be expected to act as an anchor point for the pipework. Excessive pipe stress can be a cause of vibration.

In a cold water system ( temp below 100 degress or so) the pump may be connected without an expansion joint because there is little or no thermal growth due to temperature. In a hot water system (140 degrees up thru 400 degrees, an expansion joint is often used to absorb thermal growth. In this case, pump discharge pressure must be contained with control rods, guides or piping loops for flexibility and / or pipe anchors.

The need for formal stress analysis should be determined by designers with extensive flexibility experience. Hot piping connecting to strain-sensitive equipment such as pumps, compressors and turbines shall be closely reviewed for possible full analysis. For other systems full stress analysis is required when the following criteria is not satisfied :

DE / (L-U)² ≤ 0.03 [see ASME B31.1, Para. 119.7 & ASME B31.3, Para. 319.4]

where,

D = Nominal pipe size, in inches

E = Total expansion to be absorbed, in inches (E = U e)

L = Developed length of line axis, in feet

U = Anchor distance (length of straight line joining the anchors), in feet

e = Coefficient of expansion, in inches/feet

May be the 1st issue of your piping design indicates a good flexibility when you measured it by the acceptance criteria of the code. Otherwise you have to make a redesign of the piping system by adding an elbow(s), loop(s) or expansion joint(s), and also you have to recheck its flexibility by the criteria indicated by the code.

Otherwise, you can proceed a computerized and full stress analysis by a recognized and sound software.

Dear Galal Elden,

REMOVAL of EXPANSION JOINT and PROVIDING A LOOP IS CORRECT and is in order.

The Expansion Joint Design depends upon several factors and any one of the parameter may be deficient, calling for replacement by expansion loop.

dhayanandhan.s