This topic can be hotly contested by some; why is beyond me. Some businesses get lazy in their approach to process safety and convince themselves that flanged piping is cheaper (and easier) than joining the pipes using welding methods. As we have discussed, welding our PRIMARY CONTAINMENT system, such as the piping, comes with many requirements to ensure we have the proper management system to ensure our primary containment system is solid. This can scare some managers into believing that flanged piping is cheaper and easier. And to be honest, they could not be more wrong. We see vastly more LOPC events coming from flanged piping than we do welded piping and this is almost always traced back to this mindset that flange is easier/more straightforward; thus… we can do this all in-house with no special tools or training for our people. WRONG!
Look at this “manufacturer’s recommendation” (i.e., RAGAGEP) for installing their gaskets. This cut sheet is from a fatal LOPC event we were involved in way back in 2012 and has since been settled. The manufacturer is VERY CLEAR about how their product must be installed; you can guess these instructions were NOT followed and it was determined this was a causal factor in the accident.
I know the word “torque” is a 4-letter word to some, but it matters in process safety!
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TECHNICAL RECOMMENDATIONS for correct gasket assembly, bolting, and compression FLANGE INSPECTION 1. Ensure flange faces are clean and free from imperfections. These could be detrimental to the sealing performance.
BOLTING RECOMMENDATIONS 1. When utilizing torque wrenches, the use of suitable lubricants on the stud threads and nut bearing faces is recommended (e.g., Molybdenum di-sulphide or Nickel powder and anti-seize compounds). 2. We recommend a 4-stage tightening method as follows: 1) Tighten the bolts at 30% of the final loading using the diametrical sequence. 2) 60% of final load following diametrical sequence. 3) 100% of final load following diametrical sequence. 4) 100% of final torque on adjacent bolts.
Tables on Resultant Bolt Stress and Required Gasket Compression are given on the reverse side.
NOTE: I am intentionally keeping the company name out of this article, but their instructions are spot-on and in line with other manufacturers. |
Did you notice the 4-step process? 30%, 60%, 100% and 100% on adjacent bolts? Notice the required pattern?
It all makes a BIG difference! Not having a torque wrench, not having personnel trained on the use of a torque wrench, and not having the torque wrench in a quality program/PM program that meets the torque wrench manufacturer’s requirements are all common failures in this installation and maintenance program for flanged piping.