How to Perform a Damage Mechanism Review
By Tazim Rehmat, ABS Group Principal Engineer of Process Safety, and Randy Montgomery, ABS Group Senior Director of Midstream and Downstream
This article was adapted from the paper, "Effectively Addressing the Results of Damage Mechanism Reviews in a Process Hazard Analysis: A Checklist Approach," which was presented at AIChE's 13th Global Congress on Process Safety in March 2017.
Performing damage mechanism reviews (DMRs) to determine credible degradation modes and susceptibilities of processing equipment has become an important step in developing effective mechanical integrity plans in the refining and chemical processing industries. DMRs aid in formulating inspection plans to mitigate risk from loss of containment and/or unplanned outages and are the subject of the corresponding API Recommended Practice (RP) 571. In addition, California OSHA's (Cal/OSHA's) recently revised Process Safety Management (PSM) for Petroleum Refineries regulation now requires that DMRs be performed and process hazard analyses (PHAs) address DMR reports that are applicable to the process unit being analyzed.
The following process for performing DMRs includes insights from our Safety, Risk and Compliance team.
How to Perform a DMR
1. Obtain Data
Data required in performing a DMR include process data, operating data, and equipment/piping
design/fabrication data. Site-specific information associated with risk-based inspection studies, preventive
maintenance inspections, results from inspections, and failure history should be available electronically for
reference during the study.
2. Develop Information
A DMR includes (1) generating a corrosion materials diagram, (2) preparing a DMR worksheet, (3)
identifying initial corrosion loops, and (4) identifying potential damage mechanisms.
Developing corrosion loops is an important step in performing a DMR. A corrosion loop is defined as a
section of a process that shares common damage mechanism susceptibilities with similar anticipated rates
of damage. A corrosion loop is typically comprised of similar materials exposed to similar
process/environmental conditions and asset characteristics (materials of construction, insulation type,
coatings, heat tracing present, buried, etc.).
Corrosion loops are developed using the following guidelines:
- Maintain a single process chemical (for example, a major indication of a loop boundary is when the service that is flowing through the piping undergoes a change that greatly affects the composition)
- Maintain a single phase
- Use the inlet/outlet of a major piece of equipment (pressure vessel, separator, heat exchanger, column, etc.) as a loop boundary
3. Conduct DMR
A DMR team typically includes a corrosion engineer/specialist, unit inspector, unit process engineer, unit operations representatives, unit mechanical/reliability engineer, unit subject matter experts for licensed technologies (if needed), and a facilitator knowledgeable in the DMR process. The team (1) conducts a
process overview, considering operating and maintenance procedures, and (2) collects unit-specific process
data and discusses mechanical failure history.
The steps in conducting a DMR include:
1. Developing color-coded process flow diagrams (PFDs) to illustrate various corrosion loops in each process. PFDs, P&IDs, piping isometric drawings, and process stream heat and material balances are normally used to generate color-coded PFDs.
2. Collecting materials of construction and fabrication records to be added to the PFDs so corrosion
materials diagrams (CMDs) can be developed. The CMD is a modified process flow diagram or
database containing relevant equipment and piping corrosion mechanisms, operating conditions,
materials of construction, and corrosion circuits.
4. Identify Damage Mechanisms
Damage mechanisms are identified from a review of established corrosion/materials literature, companyspecific
studies, and industry guidance documents such as API RP 571 .
API RP 571 classifies damage mechanisms into the following major groups:
- Mechanical and Metallurgical Failure Mechanisms
- Uniform or Localized Loss of Thickness
- High Temperature Corrosion (>400 degrees F [204 degrees C])
- Environment – Assisted Cracking
Expected damage rates, susceptible locations, and susceptibilities to damages are documented, and
recommendations are developed as needed.
5. Document DMR
A DMR report contains the information needed to understand materials damage issues in a specific type of
operating process unit at a plant site. The detailed DMR report includes corrosion loop drawings, corrosion
damage mechanism tables, and documented findings and recommendations from the DMR. It is
recommended that the report include the team member composition, the DMR approach, and data used in
performing the review.
6. Use DMR Results
Once completed, the DMR report can be used in a variety of ways, including (1) inspection plan
development, (2) corrosion monitoring location (CML) placement, (3) integrity operating window
development, (4) PHA meetings, (5) management of change reviews, and (6) incident investigations.
The Value of Conducting and Documenting DMRs
While conducting DMRs and incorporating their results in PHAs and other elements of a process safety
management framework are not currently required by most regulatory agencies, state regulators in
California have begun requiring them for refineries. As industry continues to recognize the value of conducting and documenting DMRs to enhance mechanical integrity programs and mitigate the risk of loss of containment events, the results of these DMRs can also provide additional relevant information for assisting PHA (and management of change) review teams in identifying potential hazardous scenarios for processes.