Plant Operations/Maintenance/nut and bolt


We tested(shell and tube test) our heat exchanger okay but after a while we found some nut and bolts are loose.
We would like you to let us know the estimated reasons for this matter.
We think this bolts were loosened after test as we had no leakage while testing but it is strange for us.

ANSWER: Hi this is a normal reaction to thermal expansion and or vibration. When the exchanger cools the bolts contract or shrink. This process creates internal leaks within the exchanger. I have always added a preventative maintenance rountine that checks these bolts at regular intervals. Improper torque may also be the cause, something to check. If you know from past inspections that the bolts come loose monthly then have them checked weekly. Another fix would be to use finer threads on the bolts with a lock nut or lock washer. Another indication of loose bolts is oil mixed the water within the exchanger.  
I hope these ideas help.
Sincerely Mike Biro

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QUESTION: Hello my friend,
You are completely correct if the exchanger experience thermal expansion.
However,please be kindly informed that the bolts came loose after testing by water but before exchanger operation.This means the exchanger did NOT experience any cooling and heating.
We tested the exchanger okay with water.Next day we found some bolts came loose.This is strange for us.

Hi thank you for the additional Information. I would re torque the bolts and return to operation than do an inspection after about a day. keep an eye on it. It almost seems that the bolts were not properly torqued prior to your test. I hope this helps. If they continue to come loose look at the previous suggestions to remedy the problem. Thank you  Mike  

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Mike Biro


I can answer any questions on Mechanical technology. Rigging, shop practices, Hydraulics, Pnuematics,Gears, bearings, belts, fasteners, Safety, Machine tools. Anything within the scope of the Millwright Apprenticeship. All areas of plant maintenance.


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