Last week, we published the first part of this article, with 3 common reasons for mechanical integrity citations in Process Safety Management (PSM) audits. In this installment, we cover an additional 4 issues to look out for. Avoiding mechanical integrity citations in PSM audits is possible, just look out for these issues:
Mistake #4 - Failure to identify critical instruments
In many situations, no criticality analysis of instruments has ever been performed. The problem with not doing a criticality evaluation is that the instrument department can easily be overwhelmed with work if all instruments require the same calibration frequency.In such situations, critical instruments often go without maintenance and calibration until it becomes apparent that they are not working. If instruments are ranked by criticality, then maintenance and calibration can be performed at increased frequency on important instruments. This is a more intelligent use of available resources.
Mistake #5 - Failure to re-evaluate safety systems after debottlenecking
Often, process systems were modified for higher throughput after initial construction but before 1992 (when the PSM standard and its MOC requirements became law). In such situations, it is common for the original, legacy relief devices and trip systems to still be in use. If these systems have not been recalculated for current pressure, flow, and speed requirements, they may not be sufficient to provide safety when needed. During audits, all safety-critical equipment should be reviewed to make sure that the calculations accurately reflect current operating conditions.
Mistake #6 - Failure to identify safety-critical manual block valves
Manual block valves are expected to be gas-tight or liquid-tight when closed. All block valves can eventually corrode, erode, or wear, though. When worn, manual block valves can leak through.
In some situations, leak-through can result in catastrophic consequences. Despite this, few companies have done an analysis to identify their safety-critical manual block valves. Even fewer companies have a periodic replacement or inspection program. Failure of manual block valves has resulted in major explosions. A safety-critical manual block valve identification and maintenance program is now recognized and generally accepted good engineering practice.
Mistake #7 - Failure to verify quality control on incoming spares
Manufacturers can change product specifications without notice. Neither the manufacturer nor the distributor is legally obligated to notify the end user of changes in performance, materials of construction, or reliability. Many MI programs fail to specify who is responsible for quality control on incoming warehouse spares. The responsibility is often left to the “qualified vendor,” but no audits are done to verify that the vendor is actually doing what is expected.
Not only piping metallurgy, but also instrumentation, rupture discs, rotating equipment, and the remainder of safety-critical warehouse spares must be held to quality standards. Someone must be designated to be responsible for verification. The process must be audited on a periodic basis to ensure that the system is working.
Stay tuned next week, when we cover the last 5 mechanical integrity mistakes you should avoid.
