2021 RETA Breeze May-June

conducted 12 months prior, and assumptions that ‘old’ components would be the first ones needing to be replaced. Their first task was to remove insulation on the piping associated with the 12 oldest blast cells in the system. Based on visual inspection of older in-service piping (primarily visual evidence of corrosion), new piping was prefabricated, and work began to replace this older piping and equipment. Before completing the replacement work, they decided to have non-destructive testing performed to justify the work that was being done. The data from testing revealed a different story. The replacement of the ‘oldest’ piping associated with the 12 blast cells did not minimize risk to the plant. The testing results revealed that at a 40% wall loss replacement threshold, 9 of the blast cells did not need to be replaced, resulting in an unnecessary expenditure totaling $675k. The results redirected their strategy for the remainder of the first phase. They were able to make decisions based on concrete data instead of forecasting and assumptions. Their resulting cost avoidance equated to half of their original $10M budget. Deciding to Keep or Replace If you are documenting procedures for your Process Hazard Analysis (PHA) or need to document that your equipment (piping, vessels, valves, etc.) are working in a safe condition for your PSM or RMP program: 1. DO NOT try to calculate a future state, estimate damage, or assume degradation based on age. 1. DO evaluate and make decisions based on the present state. 2. DO consistently evaluate per the recommended 1- and 5-year PSM cycles. 3. DO make equipment keep/replace decisions based on remaining wall thickness measurements, not presence of corrosion.

Insulated piping does not corner the market on vulnerability; uninsulated piping is also susceptible to corrosion. For example, moisture creeps into the cracks in paint on the surface of pipe forming corrosion blisters underneath the paint that continue to get worse over time. This damage mechanism, external corrosion due to exposure to the elements, presents a non-controllable variable. There is no way to determine how quickly the moisture will accumulate or advance along piping. Because steel only corrodes in the presence of liquid water, temperature plays a significant role in the corrosion rate of piping and vessels in ammonia service: • If water is in contact with steel above the freezing temperature, corrosion will occur. • Warm steel corrodes faster than cooler steel. • If ice forms at the steel surface, corrosion will stop until the steel becomes warm enough to allow the ice to melt.

Temperature variations can be due to process cycles like defrosting an evaporator or can be environmental like seasonal snow and rain exposure. External corrosion occurs at a very inconsistent rate, and therefore, the rate at which external corrosion thins pipe wall in an ammonia refrigeration system to find remaining life of the pipe is not calculable. Field Example To illustrate how assumptions and age of equipment are not a reliable means to establish the integrity of your system, consider this case at a food manufacturing plant in Arkansas: The system, built in the 1960’s with parts transferred and installed over the years, needed a full evaluation. The size of the system (300,000+ lbs. of ammonia) called for a phased approach. The core team at the facility decided to address what they assumed to be the biggest area of weakness first – the oldest piping and valves associated with 36 blast cells. The facility’s strategy was to assess based on age, assuming the oldest components presented the largest threat. Funding was allocated based on results of the MI audit

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