Dear members,

Below is on filed situation in one of the chemical plant,

The piping is of jacketed pipe with below details,

Core pipe size : 80 NB / Duplex SS
Outer pipe : 150 NB / Carbon steel

Process condition :

Core pipe : Ethylene Oxide / 2 Deg C to 7 Deg C

Outer pipe : Chilled water : 5 Deg C to 10 Deg C

Insulation : 80 mm thick and foam glass

The chilled water flow is of counter flow arrangement. The entire jacket piping is of welded construction. Not much of information is available on jacket to core pipe anchor location. However every 6m there is a spider arrangement connecting core and jacket piping. Only one chilled water inlet for 2-3km jacket piping ( i.e. no jump over piping) . Ther are few falnges noted in the piping system

The pipe line is routed from the EO storage area to the other chemical units, which is approximately 2- 3 km distance. The entire pipe is routed in pipe rack and off -site pipe sleepers. The pipe routing has adequate expansion loops to take of thermal expansion. However there is a strange phenomena observed on the pipe rack horizontal pipe section ( The pipe rack is 120 m long) that the pipe is vertically lifted-off about 100mm along with the supports over the span of 40-50 meter. ( This problem exist quite some time) Based on the preliminary analysis considering the above indicated process condition, the computed vertical lift-off in worst case is 5-10mm on pipe change in elevation from grade level to pipe rack entry location.The computed results are far way from the actual condition of the pipe.

We are in the opinion that some up-set condition might have caused the issue ( inproper temperature distribution in jacket pipe, flow issue, line stat-up and shut down procedure)


Any suggestion to identify the possible cause of the issue.

Thanks
MNK

MNK,

The probable cause of liftoff of the section of piping in the pipe rack could be due to thermal bowing. The lower surfaces of the jacket pipe are being kept cold by the chilled water, 5 to 10 deg C, while the upper surfaces of the jacket pipe could be at some temperature nearer ambient.

The pipe rack is higher elevation than the pipe sleepers, so that any air or vapor in chilled water would collect there in the pipe rack portion of the pipe run. The collected air prevents the cooling of the upper pipe surfaces by the chilled water, and so the upper portion is at different thermal contraction (expansion) than the bottom of jacket pipe. There is probably some contributing tension loads from the duplex SS gut pipe that contracts more (more thermal change in length, decrease) than the jacket pipe, to compress the jacket pipe to be deflected in a shape of buckling column. This assumes there is not an expansion loop in the jacket pipe on the pipe rack. There is probably not a concern about over-stress of pipe, but it is good to be careful in handling ethylene oxide.