Minor Modifications can catch you out

The size of a change, either physical or financial, bears no relation to the magnitude of the hazard or risk which may be created. How confident are you that minor modifications are properly managed on your plant? Unmanaged minor modifications are often identified as a root cause during incident investigations. Here are a few examples of some small changes that can lead to disaster.

  1. A restriction orifice plate that is part of the process safeguarding system is removed during maintenance and not replaced
  2. A block valve on the outlet of a vessel has it’s solenoid replaced by one of a different size causing the valve to close too quickly thus creating the problem it is designed to solve
  3. The trim on a control valve is changed to debottleneck part of the plant. The failure of this valve is the sizing basis for a downstream PSV
  4. A pump is replaced by another nominally identical one from elsewhere on the plant, identical but the impeller on the original pump had been trimmed to prevent an overpressure
  5. An item is replaced by one of an incorrect material resulting in accelerated corrosion.

Many minor modifications can be carried out by a maintenance technician unwittingly in the normal course of his or her activities. Can they happen without raising a “red flag”? Here are a few questions to ask yourself regarding small changes:

  1. Do you have a “Process Safeguarding Manual” which physically identifies every safeguarding feature in the plant including the sizing basis for all PSV’s?
  2. Are all safety related items physically identifiable on the plant?
  3. Do you give every change some level of review by a competent person?
  4. Is the term “Like for Like” clearly identified and understood?
  5. Are minor changes included in your MoC system?
  6. Are maintenance technicians and process operators trained in MoC?

Interested in assessing your own management of change process? Have a look at this checklist

Download MoC Checklist