Return to service and start up: An effective shutdown is followed by an effective startup. During startup, the HTF system is filled to normal operating levels from the lowest point possible. Using standard operating procedures, establish circulation through the system; full flow through the expansion tank will facilitate removal of residual air and moisture from the system.
Gradually heat the system; use caution when above 212°F since any water in the system will begin to vaporize. A prudent approach is to heat the system assuming excessive moisture is present. Continue circulating fluid through the expansion tank with the vent open to allow moisture to escape to a safe and acceptable location. Holding the temperature steady while venting will prevent sudden and potentially violent reactions to vaporizing water. After effectively removing the moisture, proceed with the standard heat-up sequence for the heater.
Operations personnel should periodically walk along the piping pathways looking for leaks, paying special attention to areas where work was performed. Leaking flanges on high-temperature systems might require a shutdown so repairs can be made at cooler temperatures. A majority of flange leaks can be attributed to stresses induced from thermal cycling. It is quite difficult to achieve a leak-free flanged connection if flange faces are under severe tension or have faces out of square due to thermal expansion of the piping. After verifying the exposed piping flanges are free of leaks, insulation can be re-applied.
The secret to success
The keys to uneventful repairs of high-temperature heat-transfer systems involve safely shutting down a process using standard procedures, then developing the proper approach to manage the risks that are present. Once the risks are effectively addressed, routine repair techniques can then be applied. Using the input from a network of safety professionals, industry standards and fluid specialists, an effective and successful approach to the task is within reach.
Conrad E. Gamble, P.E., is marketing technical service principal for Solutia Inc., St. Louis, Mo. E-mail him at email@example.com.