Pressure Damage in Pipeline

[Munequip]

We have a stainless steel in line vessel installed in a pipeline. The units were designed to handle an operatitng pressure of 28 PSI with a 1.8 safety factor, and were tested at 60 PSI test pressure ~ 5 years ago. The cross section of the vessels are rectangular and have welded reinforcement on the top, sides and bottoms. Each end has a transition piece to connect to a pipe flange. The physical size of the rectangular portion of the unit is ~ 4' x 12' x 2' tall. The flow ranges between 10 and 22 MGD, and the operating pressure rangees between 14 and 28 PSI.

The units have been in operation coninuously for the last 2 1/2 years. Approximately 1 week ago, the units were damaged. It appears that the bottom of the unit was pushed down to make a bowl, and the welded reinforcements on teh bottomm of the units were bent out of position and the welds were cracked and broke. The discharge end of the unit experienced more damage than the inlet end.

This vessel is located in a pipeline that is ~ 6 miles long. The flow scheme for the system are pumps on a VFD, check valve, through the vessel, plug valve, then through a 6 mile pipeline to discharge point. There are also isolation valves for each component.

My question concerns failure of the vessel, and expected types of failures. Would someone suspect a different type of failure (i.e. pinhole, single weld break, etc) if the unit was reinforced improperly, or is the overall failure of the unit more to do with long term fatigue? What type of damage would be expected if water hammer occured?

Any thoughts are appreciated.

 

[unclesyd]

Sounds like you had surge/hammer in the line that caused severe overpressure in the line. It also sounds like the vessels are scrap.
Is there any reason not to have a round vessel constructed according to some pressure vessel code?

There is no mention of relief valve in the line.
In there one in the line?


Normally on cases where you have a fabricated piece of equipment you would expect to have leaks before failure. One would never expect to see the reinforcement move under any conditions of normal operation.

 

[BigInch]

Got pictures?

With a VFD controlled pump is a bit more difficult to pin a surge on the pump, so maybe the plug valve was closed too fast. Do the valves have actuators? If so, how fast will they open and close the valves?

What's the pipeline's diameter, normal flowrate and normal operating pressure?

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