It has become apparent that some equipment damage mechanisms may be overlooked in the performance of PHA studies. Table 1 provides examples of process safety incidents that resulted from such causes. The Division of Occupational Safety and Health within the California Department of Industrial Relations has amended its process safety management (PSM) regulations for petroleum refineries in California to include requirements for conducting damage mechanism reviews (DMRs) to be addressed in PHA studies. Also, API Recommended Practice (RP) 571, Damage Mechanisms Affecting Fixed Equipment in the Refining Industry, addresses the subject.
A damage mechanism is a mechanical, chemical, physical, or other process that results in equipment or material degradation. Table 2 provide examples of different types of damage mechanisms. Damage mechanisms may cause the failure of process equipment resulting in loss of containment or impaired operability of equipment. They may cause damage to equipment and materials that contain process fluids such as piping, pumps, and valves; equipment and materials that provide safeguards against process incidents, such as fireproofing, dikes, and deluge systems; and equipment and materials in utilities and support systems whose failure may impact on or result in a process safety incident. Damage mechanisms can arise internally or externally such as from internal or external corrosion.
Damage mechanisms may influence not only the equipment that contains hazardous materials, such as tanks and reactors, or through which hazardous materials flow, such as piping, valves and pumps, but also safeguards for a process, such as deluge systems. Some safeguards may be in contact with process fluids, such as flame arresters, while other are not, such as barriers and fireproofing. Damage mechanisms can exist for either case.
Damage mechanisms can affect not only equipment or materials made from metals, including alloys, but also others, such as polymers, including plastics; ceramics, including refractories; composites, including concrete; and glasses. DMR reviews must consider all materials of construction that may be subject to damage mechanisms, for example, not just piping but also fittings, connectors, and welds.
Damage mechanisms may apply to a particular part of a process or throughout a process, that is, they may be local or global. For example, one particular vessel may be susceptible to low temperature embrittlement but piping throughout a process may be susceptible to corrosion.
A DMR involves identifying damage mechanisms that exist for a process and examining all parts of a process for their susceptibility to the damage mechanisms. It is performed before a PHA study to identify those damage mechanisms that are believed possible for a process. This information is provided to the PHA team for their consideration during a study. The results of DMRs help to provide more comprehensive identification of hazard scenarios in PHA studies. DMRs are valuable not only for petroleum refineries but also for any facility where equipment failures may result in catastrophic accidents.
Table 1. Examples of Incidents Involving Damage Mechanisms.
| Incident | Consequences | Damage Mechanism |
| Esso Gas Plant, Longford, Australia, 1998 | Explosion and fire. 2 fatalities, 8 injuries. Destruction of one plant and shutdown of two others. Loss of gas supplies to businesses. | Low temperature metal embrittlement |
| Bethune Point Wastewater Treatment Plant, City of Daytona Beach, FL, 2006 | Explosion and fire. 2 fatalities, 1 critical injury. The aluminum flame arrester on a methanol tank had corroded to the point that it no longer functioned. | Corrosion of aluminum by methanol |
| Silver Eagle Refinery, Woods Cross, UT, 2009 | Explosion that damaged nearby homes. | Sulfidation corrosion |
| NDK Crystal, Inc., Belvidere, IL, 2009 | High-pressure vessel rupture. One public fatality, one public injury. | Stress corrosion cracking. Temper embrittlement, or some other form of heat treatment embrittlement, may have been a contributing factor. |
| Tesoro Petroleum Refinery, Anacortes, WA, 2010 | Explosion and fire. 7 fatalities. | High temperature hydrogen attack |
| Millard Refrigerated Services, Theodore, AL, 2010. | One employee and 152 offsite workers sustained injuries. 32 workers were admitted to the hospital, and four were placed in intensive care. | Hydraulic shock |
| Chevron Refinery, Richmond, CA, 2012 | 15,000 members of the public sought treatment for various ailments including breathing problems. Approximately 20 people were admitted to local hospitals as inpatients for treatment. | Sulfidation corrosion |
Table 2. Damage Mechanisms.
| Type | Examples |
| Mechanical loading failures | Ductile fracture, brittle fracture, mechanical fatigue and buckling |
| Erosion | Abrasive wear, adhesive wear and fretting |
| Corrosion | Uniform corrosion, localized corrosion and pitting, sulfidation corrosion |
| Thermal-related failures | Creep, metallurgical transformation and thermal fatigue |
| Cracking | Stress-corrosion cracking |
| Embrittlement | High-temperature hydrogen attack, low temperature metal embrittlement |