Cold Piping Event during New Plant Startup:Do You Have All the Details You Need for Your PHA?

As a part of the new 500 kta ethylene plant constructed for Shintech in Plaquemine, LA, the operations team with support from the project team and engineering disciplines completed a comprehensive PHA of all parts of the plant including the hot side, cold side, utilities and co-product loading. A HAZOP process was utilized and vessel drawings, P&IDs and other process information was utilized as much as possible.

During startup, the Cold Board operator received a low temperature alarm for a section of carbon steel piping with the lowest temperature showing -80 deg C. The line was depressured at the same time that an in field investigation was conducted to try and determine if the reading was real and if so, what the possible cause was. It was determined that liquid ethylene had built up in a line of pipe and leaked across a large block valve. The key detail is that the PHA had not identified this failure mechanism because it was equipment design specific at a level of detail that was not in the drawings available to the PHA team, and it could only occur during startup. Do YOU have all the details you need for your PHA? Fortunately, there were no significant consequences for this event due to rapid recognition and response by operations and maintenance.