#5 – Gasket Surface Damage…
If your facility utilizes shell and tube heat exchangers, chances are you’ve experienced damaged gasket surfaces that create leak paths for your process. Scheduled maintenance typically involves removal of bonnets and flanges for inspection and cleaning. You’ve probably witnessed a flange or bonnet shift during removal and crash into the tube sheet, damaging one or both flanges. It is best practice to address these areas immediately to avoid unnecessary down time by “rolling the dice” and putting it back together with a new gasket, crossing your fingers and hoping it seals.
Generally, it’s not a major undertaking to perform the repair if you have the right equipment and knowledge. The cost to do nothing can be far greater than the cost to repair should the unit leak upon startup, since at that point you must shut things down and disassemble everything just to get to the problem spot in order to affect the repair.
In addition to using the right equipment, it is also critical to understand the damage and determine if welding should be performed before machining the gasket surfaces. If too much material is removed to achieve the repair during machining, you can end up with a bolted joint that is under minimum thickness, resulting in poor sealing or – worse-case – a unit that is no longer to code. Working with a repair company who has the experience, staff and software to determine maximum material removal as well as the ability to perform a weld repair under NBIC guidelines can save you untold trouble down the road.
It’s important not to forget the potential need to machine pass partition grooves (or pass partitions) after machining the circular gasket face. The best results will occur if all the gasket surfaces are in the same plane to avoid pinching the gasket and introducing bypass flow around the pass partition.
Gasket surface damage is a fact of life in most manufacturing environments. Arm yourself with the necessary knowledge and the best contacts of those to call who can be a resource during the repair process.