Accurate process flow, piping and instrument diagrams are important beginnings to a PSM plan. They show employees and contractors the entire system as well as the relationships among equipment, piping, valves and instrumentation. However, facilities often will implement system changes or add or remove piping lines without updating their drawings. Instead of being the roadmap to the plant, these drawings become a safety hazard with potentially disastrous consequences. Inaccurate drawings have been the cause of significant accidents when workers cut into the wrong line, fail to properly isolate lines during tie-ins, or mistakenly open or close valves. It is essential that drawings are updated after changes have been made to the mechanical systems and equipment.
Labeling of the lines can be a considerable help in this process and can be achieved while the piping and instrument diagrams are being updated. In both cases, lines need to be walked down and documented. Red lining changes to existing drawings can be documented at the same time that the legends, sizes and quantities of labeling materials are being compiled. Combining these two projects will save time and money, whether the work is performed in-house by technicians or is outsourced to contractors. A second benefit to completing the labeling process while plant drawings are being updated is that any subsequent changes to piping or equipment will be visible even if drawing updates are not made. Since the changes will not be labeled, they will stand out by omission.
One comment often heard from people who don't mark their systems is, “I have been here forever, and I know the system like the back of my hand.” This situation would be ideal if those employees were on site 24 hours a day, seven days a week. However, when these knowledgeable people go home after their shift, take vacations, leave to go to another job or retire, the plant becomes vulnerable if the remaining staff doesn't have the same experience. The employees are forced to trace lines to find a valve, perform routine maintenance or shut down a system during emergencies without benefit of years of knowledge of the system. This process takes time and can cause delays in an emergency response situation.
Labeling an Ammonia Refrigeration SystemInternational Institute of Ammonia Refrigeration (IIAR) Bulletin 114 includes recommendations for marking an ammonia refrigeration system. A standardized plan should be implemented, documented and followed so that all workers can understand what the marks mean.
The pipe identification should clearly indicate the contents of the pipe and the flow direction. IIAR Bulletin 114 calls for the system to be shown (black letters on a yellow background), along with the state of the contents (Liquid -- LIQ, black letters on a blue background, or Vapor -- VAP, black letters on a blue background), the type of coolant (most commonly AMMONIA, black letters on a yellow background), the pressure of the line (HIGH, black letters on a red background, or LOW, black letters on a green background) and the flow direction (black arrow on a yellow background). It also recommends the overall size of the marker based on the pipe's total outside dimension, including insulation.
At the least, each valve that is tagged should have a unique number. Other information a plant should consider including on the valve tags is the line (HSD, RV, etc.) and whether the valve is normally open or normally closed (NO or NC). Some companies use the drawing number associated with the piping and instrument diagram on their tags. However, if the drawings are changed, then all the valve tags would need to be changed as well so that the PSM plan can be followed.
The American Society of Mechanical Engineers (ASME) A13.1 standard provides color and size recommendations for the utility system. Both the ASME and IIAR standards are understood throughout all types of industries and are good guide for companies that need to establish an identification standard as part of their PSM.
Labeling ConsiderationsAny materials used in a marking project should be able to withstand the plant's environmental conditions and last for a number of years. Marking a system once is a major project; going back and doing it all over again due to the failure of material used for the pipe markers, valve tags and signage is a waste of time and money.
Considerations include the ambient temperature in which the marking materials will be used, whether the materials will be indoors or outside, and whether they will be exposed to chemicals or subject to frequent wash downs by high-pressure hoses. A plant might also have special conditions that should be taken into account when selecting marking materials.
Once these factors have been identified, the facility operator should find a product that will meet the plant's needs. If an outside contractor will handle the marking project, the chosen marking materials should be included in the project specifications.
Some facilities prefer to mark the system using their own personnel. The pitfall to this plan is that there is usually a “hotter fire to put out,” and the marking that was started with such good intentions is never completed. Facilities that are short on staff or uncertain how to proceed might want to consider outsourcing the entire project to an experienced marking services provider that can develop a marked system that is compliant with the company's PSM.
Some facility operators and owners might think that marking their system is an expense that they cannot afford right now but will eventually get to “in the future.” However, clear, complete system marking is vital to an effective process safety management plan. Making a small investment in system marking now will pay enormous dividends in overall plant safety. PCE