Many times centrifugal pumps and their electric motors fail due to pipe stress. Follow this procedure and stop self induced failures.

1. Eliminating Pipe Stress
“GANG BOX TRAINING”
Maintenance Supervisors should use this tool to train their maintenance techs, welders and
contractors - 10-20 minutes – Post them in the Maintenance Shop after use
Pipe stress is caused by misalignment of the 2. Validate misalignment to insure motor and
mating surfaces of two pipe flanges creating pumps shafts are aligned to specification.
abnormal internal stress of pump bearings, seals, 3. Disconnect the outlet flange on the pump.
motor bearings, couplings, and can possibly change 4. Revalidate laser alignment of shafts.
the displacement of a pump. 5. If alignment has moved then you have pipe
stress. Do the same for the inlet flange.
General Rules which must be followed by 6. Make corrections as stated in the following
maintenance personnel and contractors: procedures to eliminate pipe stress.
(if you want to stop self induced failures)
Elimination of Pipe Stress – The Ricky Smith
1. Pipe Flanges attached to pumps must be aligned Method as learned from Dan Turner (my
where the gap does not exceed the thickness of maintenance and engineering manager at Exxon
two gaskets or tolerance established by your during the 1970s)
company’s engineering standards.
2. Pipe flange bolts must drop in without 1. Bolt flanges to pump and insert blind flange
assistance. gasket along with two regular flanges
3. Cable pullers, come-a-longs, or long bars should between pump and mating flanges. (cover
not be used when aligning a flange which is the hole between welding area and inside
connected to a pump. the pump)
4. Validate the elimination of pipe stress by 2. Attached welding ground to flange. (do not
following the procedure below. attach ground lead to pump; welding group
must always be attached to flange)
Failure Modes experienced from Pipe Stress on Warning: failure to accomplish this one
Bearings: task properly will cause bearing failure by
- Wear caused by seals leaking “electric arcing” which is a failure mode
- Wear caused by static vibration of bearings.
- Indentations caused by overloading while 3. Tack weld flange into place reverse welding
static each tack.
- Corrosion caused by inadequate lubrication 4. Allow to cool for 10 minutes.
caused by abnormal loading (seal leaking) 5. Reverse stitch weld on opposite sides on the
- Flaking caused by misalignment and flange similarly used for cast iron welding.
excessive loading 6. After initial reverse stitch weld then weld
normally using electrode recommended by
WARNING: Ensure your contractors follow the the American Welding Society (typically E-
same process to eliminate pipe stress. Pipe stress 6010 5P or GTAW.
elimination should be validated during 7. After root pass; weld in any direction you
commissioning of new pump. wish.
8. Allow to cool and then disconnect flange,
Follow this process if you want to inspect your replace gaskets and;
pumps which may have pipe stress: - Validate bolts will drop into holes without
pry bar
1. Align the two shafts between your pump and - Validate gap between flanges is no more
driver (typically an electric motor) to tolerance than two gaskets thick.
recommended by the equipment vendor or your If you have questions send me an email at
company’s engineering standards. rsmith@gpallied.com
Page 1 of 1 GPAllied
4360 Corporate Road
“When commissioning any new existing pump use Vibration Analysis to Suite 110
ensure there are no identifiable defect on the pump or motor” Charleston, SC 29405
www.gpallied.com Office (843) 414-5760
Fax (843) 414-5779
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