C r i t i c a li li t y - B a s e d M a i n t e n a n c e Criticality-Based Maintenance (CBM) is a four-step process of identifying and addressing risk and exposure in a facility. These steps are: are: 1. Equipment Criticality Ranking (ECR) 2. Follow-up action plans 3. Implementation of approved action plans 4. Close-out of completed action plans CBM is consistent with the following industry standards: API RP 580: Risk-Based Inspection NFPA 704: 704: Standard System for the Identification of the Haz ards of Materials for Emergency Response 1910.119: Process Safety Management OSHA 29 CFR 1910.119:
Equipment Criticality Ranking Equipment criticality ranking is a qualitative assessment of potential consequences associated with specific equipment items and the likelihood that those consequences will occur. Potential consequences are evaluated for each equipment item using a causeevent-consequence process. Each failure scenario is a combination combination of a cause and event, and may have one or more potential consequences. Consequences considered for each scenario are assessed and given values for consequence severity level and likelihood of occurrence (Table (Table 1, 1, Table 2, 2, and Table 3). 3). Likelihood is based on a generic equipment case, i.e. what is typical for the specific type of equipment. The consequence and likelihood values for each consequence consequenc e are entered into a risk-rating matrix to give a risk rating value (Figure (Figure 1). 1). The risk rating for a given equipment item is the worst case rating for all consequences considered. Risk ratings are generated separately separately for hazard and process consequences and the respective process and hazard rating values are entered into a risk-ranking matrix to give equipment criticality rankings (Figure (Figure 2). 2). Risk ratings are also used to assess an order-of-magnitude level of exposure in monetary terms (Table (Table 4). 4). Exposure is only present at the equipment items where the consequences occur and must be assessed in that manner. For example, a pressure vessel protected by a relief valve has a given level of exposure. The relief valve may cause an overpressure situation in the vessel if it fails to function, but itself does not have associated exposure. Figure 1. Risk Rating Matrix e c n e u q e s n o C
VH H M L N
3 2 1 0 0
3 2 1 0
N
L
4
5 4
Figure 2. Risk Ranking Matrix
3 2 1
6 5 4
7 6 5 4
2
3
M
H
VH VH
Frequency Page 1 of 4 January 14, 2001
R C P
4-7 4 3 2 0,1
A A B C D
A A B C C
A A B B B
A A A A A
A A A A A
0,1
2
3
4
4-7
HCR
Table 1. Safety and Environmental Consequence Categories Category Very High
High
Medium
Low Negligible
Select highest category for which one criterion is satisfied Multiple fatalities of company or associated personnel. • Severe injury, illness, or fatalities of one or more members of the community. • Catastrophic environmental impact requiring a full-scale response by outside • agencies. Death of one company or associated person. • Severe injury or illness of multiple plant personnel. • Major reportable environmental incident requiring significant company resource • commitment as defined by EH&S guidelines. Notification of regulatory agencies, negative press coverage. Any hydrocarbon, produced water, or drilling fluid spill greater than 12 bbl within the facility boundaries or any spill outside the facility boundaries. Any spill of acid, caustic, or hazardous chemicals > 0.2 cubic meters regardless of location Medical treatment required for personnel. • Minor reportable environmental incident as defined by EH&S guidelines. Any • hydrocarbon, produced water, or drilling fluid spill greater than 12 bbl within the facility boundaries or any spill outside the facility boundaries. Any spill of acid, caustic, or hazardous chemicals > 0.2 cubic meters regardless of location. Minor medical treatment or first aid required for plant personnel. • Non-reportable environmental incident. • No safety or environmental consequences. •
Table 2. Process Consequence Categories Category Very High
Select highest category for which one criterion is satisfied Major production loss. • Financial impact at a corporate level. •
High
• • •
Medium
• • •
Low
•
Negligible
•
Significant loss of production capacity (50-100%) for short term (<48 hours). Loss of production capacity (<10-50%) for long term (>48 hours). Financial impact at a facility level. Loss of production capacity (10-50%) for short term (<48 hours). Minor loss of production capacity (<10%) for long term (>48 hours). Financial impact at a unit level. Minor loss of production capacity (<10%) for short term (<48 hours). Process capability not impacted.
400,000 – 4,000,000+ BBL 7 8 $10 - $10 + USD 40,000 – 400,000 BBL 6 7 $10 - $10 USD 4,000 – 40,000 BBL 5 6 $10 - $10 USD
400 – 4,000 BBL 4 5 $10 - $10 USD < 400 BBL 4 < $10 USD
Table 3. Likelihood Categories Category Very High High Medium Low Negligible
Likelihood of Consequence
One or more occurrences are credible annually Several occurrences are credible in the facility lifetime One occurrence is credible in the facility lifetime Not expected to occur in the facility lifetime but not outside the realm of possibility Practically impossible
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Table 4. Exposure Matrix (Consequence x Likelihood) e c n e u q e s n o C
VH H M L N
1.00E+08 1.00E+07 1.00E+06 1.00E+05 1.00E+04
$1,000 $10,000 $100,000 $1,000,000 $10,000,000 $100 $1,000 $10,000 $100,000 $1,000,000 $10 $100 $1,000 $10,000 $100,000 $1 $10 $100 $1,000 $10,000 $0 $1 $10 $100 $1,000 1.00E-05 1.00E-04 1.00E-03 1.00E-02 1.00E-01
N Total Exposure
=
L
M
H
VH
Frequency/Probability Σ(Hazard & Process Risk Amounts)
Furthermore, due to the qualitative nature of the ECR assessment, careful consideration must be given as to whether the sum of the exposure of subsets of systems equals the total exposure for the system. For example, the Mainline Pipeline has been evaluated by piping segments between valve stations. The maximum consequence level associated with each segment leak was very high. The likelihood of such a consequence was considered as “Medium: one occurrence is credible in the facility lifetime,” based on that fact that such failures are known to occur in industry. It would be inaccurate to state that the level of exposure of the Mainline Pipeline is the sum of the exposure level determined for each segment. Exposure level for this item would instead be the maximum exposure level of its components.
Follow-up Action Plans Follow-up is a process of reviewing high-risk equipment items and preparing and implementing action plans for risk reduction. Figures 1 and 2 identify “Red,” “Gray,” and “White” zones associated with criticality ratings for each equipment item. Action plans should be brought forward for items in the red and gray zones; no action is required for white-zone items as they are at acceptable risk levels. In general, all red zone items should be reduced to a minimum of gray zone. Gray zone items should all be evaluated for risk reduction, but in some cases risk cannot be feasibly reduced. Preparation of Action Plans Action plans are used to identify a course of action for reducing risk; they do not include a design package for recommended changes, but rather bring forward a plan for risk reduction for approval by management. The action plan is prepared as a document that identifies the current situation and level of risk, proposed a ction, and residual risk once the action has been implemented. Actions plans should be prepared with the low-cost solution in mind. The first step is to do more detailed analyses of equipment items in question to see if action is warranted. Some review questions might be: Were assumptions too conservative? What is the specific versus generic case likelihood of the consequence? Is the design basis adequate where it was assumed inadequate in the ECR study? Are spare parts inventory levels adequate? Page 3 of 4 January 14, 2001
If analyses show that action is warranted, low cost solutions should be reviewed first. These might include: Implementation of procedures Implementation or improvement of predictive or preventive maintenanc e. Adjustment of spare parts inventory levels Exhausting these possibilities, facilities changes should be evaluated. Approval of Action Plans Action plans are presented to a management forum for approval in a “sign-off meeting.” Typical attendees at a sign-off meeting include engineering, production, and maintenance managers.
As a rule-of-thumb, a minimum of 100 actions plans should be presented at each meeting. These should be grouped for expeditious presentation, typically by type of action. Signoffs are generally done by groups of action types once management is comfortable with the basis and rationale for the respective types. As part of the approval process, action plans should be assigned to specific people and given completion dates.
Implementation of Action Plans Once action plans are assigned to the appropriate people, implementation becomes the responsibility of the assignee. However, the CBM Lead Engineer has responsibility for monitoring the status of all action plans. When risk for a given equipment item is reduced by implementing new procedures, inspections, by taking credit for protective equipment, etc., the following considerations must be taken: 1. Effectiveness of risk reduction measure. Use as a guideline the procedures outlined in API Recommended Practice 580, Risk-Based Inspection. 2. Risk reduction via procedure or inspection requires that the procedure or inspection assume the criticality of the risk that it reduced p rior to implementation of that procedure or inspection. Management of Change procedures must accompany any facilities changes.
Close-Out of Completed Action Plans After disposition of approved action plans, process safet y information (PSI) must be finalized and confirmed. Confirmation is documented by attaching appropriate copies of process safety information to an Action Plan Resolution Form. The Action Plan Resolution Form gives a statement of the initial condition, the action taken, and a summary of before and after risk. The CBM Lead Engineer signs off the Action Plan Resolution Form when the action has been satisfactorily implemented and applicable PSI updated.
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