Q & A > Question Details
Forum is requested to share its opinion about Gasket Failure events, due to sudden unit shut down, of Column bottom pumps (Operating@400°C) of thermal cracking Units. Is there any requirement that Gasket be replaced after 2 shut downs? How can sudden Gasket failures be prevented. Pls suggest some recommended practice.
20/08/2012 A: Jayaraj Jayam, Chennai Petroleum Corporation Limited, njayaraj@gmail.com
Normal way of handling shut down and start up of thermal cracking unit is respecting the rate of raise or decrease the temperature during start up or shut down. Sudden drop or increase in temperature will lead to uneven thermal expansion of flanges and this can cause leak.
During start up, hot bolting of flanges should be carried out at every stage of temperature raise. During hot bolting, hold the temperature of the system till complete the hot bolting.
Important thing in tightening the bolts is follow the sequence of tightening in such a way that the opposite bolts are coming in the sequence one after other.
In sudden shut down, temperature surge will be much more than the normal shut down or start up. Leak can be expected in this case. But gasket failure can occasionally combines with it. This can be avoided by proper lapping and cleaning the faces of the flanges and inspecting the gasket for its intact condition during box up of flanges.
20/08/2012 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Assuming you are referring to flange gaskets and not pump packing, here are two practices, one design and one operating:
1. This service requires careful pipe stress analysis of the suction piping to avoid angular thermal stress at the flanges.
2. Always immediately flush the pump with gas oil when the pump is shut down.