Risk-Based Inspection Assessment Programs

4.5.1 SCOPE

a) This section describes the basic elements, principles, and guidelines of a risk-based inspection (RBI) program. This section does not address any one method but is intended to clarify the elements asso- ciated with a RBI program. Risk assessment is a process to evaluate continued safe operation of a pressure-containing component. This process is based on sound engineering practices, proven risk assessment experience, and management principles. There are numerous risk-based assessment methods being applied throughout many industries. Details for developing and implementing risk-based inspection programs are defined in other referenced standards.

b) Implementation of a (RBI) assessment program allows an owner or user to plan inspection frequencies based on assessing probability of failure (POF) and consequence of failure (COF) (risk = POF x COF). Risk assessment programs involve a team concept based on knowledge, training, and experience be- tween engineers, inspectors, operators, analysts, financial, maintenance, and management personnel. Appropriate and responsible decisions must be made from input by all team members to ensure safe operation of systems and their components. Organizational commitment and cooperation is required to successfully implement and maintain a RBI program.

4.5.2 DEFINITIONS

COF — Consequence of failure. Outcome from a failure. There may be one or more outcomes from a single failure.

POF — Probability of failure. Extent to which a failure is likely to occur within a specific time frame.

Risk — A combination of probability of an event occurring and the consequences associated with the event.

Risk = (POF x COF).

Risk Assessment — A process of risk analysis and evaluation.

Risk Analysis — Identification and use of information such as historical data, opinions, and concerns to eval-

uate, treat, and accept risk.

Risk-Based Inspection — Inspection managed through risk assessment.

Risk Criteria — Terms used whereby the significance of risk is assessed, such as personnel safety, cost ben-

efits, legal/statutory requirements, economic/environmental aspects, stakeholders concerns, priorities, etc.

Risk Evaluation — Process to compare risk with given criteria to determine the significance of risk to assist

in accepting or mitigating the risk.

Uncertainty — A measure of confidence in the expected value. 4.5.3 GENERAL

Risk-based inspection assessment programs can provide the following benefits for organizations: a) An overall reduction in risk of equipment failure;

SECTION 4

d) Process safety improvements; by concentrating inspections, maintenance and associated expenditures on items of high risk and reducing efforts on low-risk items;

e) Improved record retention for items by retaining both historical and latest essential data and information needed for assessment;

f) Provides a management tool to continually:

1) Maintain an effective inspection and maintenance program; 2) Improve reliability and safety for operation;

3) Define staffing needs;

4) Evaluate and define funds required;

5) Adjust risk assessment program based on desired results; and 6) Manage uncertainty.

4.5.4 CONSIDERATIONS

Effective risk-based inspection programs should consider the following: a) Significance of failure to personnel safety;

b) Identifying and obtaining accurate and appropriate information on system or component;

c) Using appropriate inspection methods and types (internal, external, inservice, etc.) frequencies, and understanding limitations;

d) Design requirements; e) Installation requirements;

f) Operational requirements and limitations; g) Proper execution of plans;

h) Qualifications and training requirements for personnel; i) Use and development of procedures;

j) Sound engineering and operating judgment;

k) Effective communication among all affected areas of management and personnel; l) Jurisdictional and Inspector involvement as required;

m) Human error;

n) Consequential and secondary effects; and o) Impact of failure on personnel or operations.

4.5.5 KEY ELEMENTS OF AN RBI ASSESSMENT PROGRAM

The following key elements should be included when establishing an RBI program: a) Establish objectives and goals;

SECTION 4

b) Understand risk of operation by identifying effects of inspection, maintenance, operating parameters, and mitigating actions;

c) Defining roles, responsibilities, training, and qualifications; d) Define risk criteria;

e) Managed actions for acceptable levels of risk;

f) Understanding and meeting safety and environmental requirements; g) Optimizing expenditures;

h) Assessing mitigation alternatives; i) Data and information collection;

j) Identifying deterioration mechanisms (see NBIC Part 2, Section 3); k) Assessing POF and COF;

l) Determining an acceptable risk matrix;

m) Reassessing and updating RBI assessments; and n) Required documentation and retention.

4.5.6 RBI ASSESSMENT

Assessments provide a systematic approach to screen risk, identify areas of concern, and develop a list for needed inspections or analysis. (POF) and (COF) must first be evaluated separately. Risk is then determined as (POF x COF) to develop a risk ranking measure or estimate.

4.5.6.1 PROBABILITY OF FAILURE

Probability of failure can be expressed in terms of number of events occurring during a specific time frame. There are three main considerations when analyzing POF.

a) Evaluate deterioration mechanisms based on materials and the item’s operating environment. b) Evaluate the impact of deterioration mechanisms on the integrity of the PRI(s).

c) Determine the effectiveness of the inspection program to quantify and monitor deterioration mecha- nisms either on-or off-line, so that mitigation can be effective prior to failure.

4.5.6.2 CONSEQUENCE OF FAILURE

Consequence analysis involves logic modeling to depict combinations of events to represent effects of fail- ure. These models usually contain one or more failure scenarios. Consequence categories for consideration include the following:

a) Personnel safety;

b) Business/production effects, including cost related to downtime or collateral damage to surrounding equipment;

c) Affected area;

SECTION 4

e) Volume of fluid or gas released; f) Toxic or flammable events; and g) Maintenance/repairs/replacement. 4.5.6.3 RISK EVALUATION

Once POF and COF are assessed and assigned, categories of risk can be calculated and evaluated. A risk matrix or plot is helpful to display or present risk without using numerical values with categories such as low, medium, and high typically assigned to identify POF and COF. POF and COF categories can be presented easily to understand and manage risk. Using the risk evaluation, an inspection plan, including proposed in- spection frequencies and appropriate inspection methods, is developed and implemented.

4.5.6.4 RISK MANAGEMENT

Based on risk ranking and identifying acceptable thresholds, risk management or mitigation can proceed. When risk is considered unacceptable, the following action should be taken to minimize POF or COF. These may include, but are not limited to, the following:

a) Decommissioning;

b) Increased monitoring/inspection; c) Repair/replace/maintain;

d) De-rate equipment — needs/limits/cycles; e) Modifications/redesign;

f) Training; and

g) Enhance process control.

4.5.7 JURISDICTIONAL RELATIONSHIPS

Jurisdictions mandate specific codes/standards with rules or laws that may differ between jurisdictions. Fre- quency and types of inspections are examples of requirements that may vary. Owners and users implement- ing RBI assessment plans should understand jurisdictional requirements, so deviations from the mandated types of inspection and frequency of inspection can be requested. Methods used to develop and implement RBI assessment methods and the RBI program developed from those methods shall be acceptable to the Jurisdiction and the Inspector as required.

SECTION 5