Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
API 755-2-2016: Risk-Based Inspection (RBI) Methodology for Fixed Equipment and Piping in Refineries
Comprehensive Guide to Implementing API 755-2-2016 for Process Safety and Asset Integrity
Scope and Purpose of API 755-2-2016
API 755-2-2016 is a recommended practice published by the American Petroleum Institute (API) that provides a standardized methodology for implementing risk-based inspection (RBI) programs for fixed equipment and piping systems in refineries, petrochemical, and chemical process plants. It is part of the API 755 family of standards, which cover risk-based inspection across various sectors of the hydrocarbon industry. This specific part focuses on the detailed technical requirements and data analysis procedures necessary to design, execute, and maintain an effective RBI program for light hydrocarbon and chemical operations.
The primary purpose of API 755-2-2016 is to help operators prioritize inspection activities based on the risk of failure, thereby optimizing resource allocation and reducing the likelihood of catastrophic events. The standard is intended for use by engineers, inspectors, and asset integrity managers responsible for ensuring the continued safe operation of pressure vessels, storage tanks, heat exchangers, piping circuits, and other process equipment.
Technical Requirements
Risk Assessment Methodology
API 755-2-2016 requires operators to assess risk as the product of two key factors: the probability of failure (POF) and the consequence of failure (COF). The standard prescribes both qualitative and semi-quantitative approaches, enabling flexibility based on the availability of data and the complexity of the facility.
Best Practice: Use a semi-quantitative approach whenever possible to align the risk ranking with actual failure frequency data and economic impact models. This improves the defensibility of inspection interval decisions.
Data Requirements
A thorough RBI analysis under API 755-2-2016 depends on the collection and validation of a wide range of data. The table below summarizes the essential data categories and fields that must be considered during the assessment.
| Data Category | Required Fields | Importance Level |
|---|---|---|
| Equipment Design Data | Construction material, design pressure/temperature, fabrication date, code of construction | High |
| Process Conditions | Operating pressure and temperature, fluid composition, flow rates, start-up/shutdown cycles | High |
| Damage Mechanisms | Expected mechanisms (e.g., corrosion, fatigue, stress corrosion cracking, hydrogen damage) | High |
| Inspection History | Inspection dates, types (NRT, UT, PT, etc.), findings, remaining thickness measurements | Medium |
| Consequence Data | Contents (flammable/toxic), released quantity, detection/isolation systems, population density | Medium |
| Maintenance Records | Previous repairs, modifications, monitoring programs, leak history | Low |
Probability of Failure (POF) Calculation
The standard describes how to estimate the POF by combining a generic failure frequency for each equipment type with damage factors that adjust for specific degradation mechanisms, inspection effectiveness, and maintenance practices. The damage factor approach is central to API 755-2-2016, where each mechanism is assigned a factor (e.g., 1, 2, 5, 10, 20) based on the severity and the effectiveness of the inspection program in detecting the damage before it reaches a critical level.
Caution: Do not rely on generic failure frequencies without adjusting for site-specific conditions. The standard emphasizes the use of industry data (e.g., from API, OECD, or operator own databases) and regular updates to the POF values based on feedback from continuous inspection.
Consequence of Failure (COF) Evaluation
COF is assessed in terms of safety, environmental, and economic impact. API 755-2-2016 recommends using simplified consequence models that account for fluid properties (auto-ignition, toxicity), release scenarios (small leak vs. rupture), and mitigating factors such as isolation valve availability or blast walls. The standard provides default values for common process fluids but allows for refined analysis when more accurate data are available.
Implementation Highlights
Phased Approach
API 755-2-2016 advocates a phased implementation: first a screening-level assessment (qualitative) to quickly identify high-risk circuits, followed by detailed semi-quantitative analysis. This phased approach is especially useful for large facilities with hundreds of equipment items, as it focuses resources on the areas of greatest risk.
- Define risk acceptance criteria: The organization must establish its own threshold for tolerable risk, typically expressed as a risk matrix with categories such as High, Medium, and Low.
- Data gathering and validation: A multidisciplinary team (process engineer, materials engineer, inspector, operations) must review and approve all input data.
- Inspection plan generation: Based on the risk category, the standard defines recommended inspection intervals. For example, high-risk equipment may require inspection every 2–5 years, while low-risk items can be deferred to 10+ years.
- Documentation and review: The entire RBI analysis process must be documented, including assumptions, data sources, and risk calculations. A formal review is required at least every 5 years, or upon significant change.
Compliance Tip: To align with the standard, maintain a living RBI database that captures all inspection results and updates risk values accordingly. This is critical for demonstrating due diligence during audits.
Team Competency
The standard requires that the RBI team members have demonstrated experience in process safety, materials science, and non-destructive testing (NDT). At least one member must be a certified RBI specialist (e.g., API 580/581 certified) to ensure the methodology is correctly applied.
Compliance Notes
Auditing and Reporting
API 755-2-2016 is a recommended practice (RP), not a mandatory code; however, many regulatory bodies (e.g., OSHA PSM, EU SEVESO) consider adherence to such practices as evidence of compliance with process safety management requirements. A clear audit trail is essential, including:
- Risk assessment matrices for all assets
- Inspection records with results and corrective actions taken
- Quarterly performance indicators (e.g., number of overdue inspections, risk reduction actions)
Integration with Other Standards
API 755-2-2016 is designed to work seamlessly with API 581 (Risk-Based Inspection Technology) and API 580 (Risk-Based Inspection). Operators should also consider complementing the RBI program with API 571 (Damage Mechanisms), API 510 (Pressure Vessel Inspection Code), and API 570 (Piping Inspection Code).
Critical: Failure to integrate API 755-2-2016 with an existing management of change (MOC) system can lead to outdated risk assessments. Any process change, equipment substitution, or significant inspection finding must trigger a review of the RBI analysis. Not doing so is a frequent cause of audit findings.
Lifecycle Management
The standard emphasizes that RBI is not a one-time project but a continuous improvement process. The final compliance requirement is to establish a system for periodic revalidation—typically every 3 to 5 years—where the entire risk assessment is updated with the latest operational data and inspection results.
Operators who have fully implemented API 755-2-2016 report an average 30–50% reduction in unnecessary intrusive inspections, while focusing on the 10–15% of equipment that contributes to 90% of the process safety risk. This aligns with the primary goal of API 755-2-2016: safer, more efficient asset management.
Q: What is the difference between API 755-2-2016 and API 581?
A: API 581 is the underlying technology standard that provides detailed equations and damage factor definitions for RBI analysis. API 755-2-2016 is the recommended practice that guides how to implement RBI specifically for light hydrocarbon and chemical operations—it references API 581 and adds industry-specific guidance for data collection, team composition, and compliance documentation.
A: API 581 is the underlying technology standard that provides detailed equations and damage factor definitions for RBI analysis. API 755-2-2016 is the recommended practice that guides how to implement RBI specifically for light hydrocarbon and chemical operations—it references API 581 and adds industry-specific guidance for data collection, team composition, and compliance documentation.
Q: Can API 755-2-2016 be used for offshore facilities?
A: The standard is explicitly written for onshore refining and petrochemical plants. Offshore facilities should refer to API 2RB or other relevant industry standards, though some of the risk assessment principles in API 755-2-2016 can be adapted if proper adjustments are made for marine environments and mobilization logistics.
A: The standard is explicitly written for onshore refining and petrochemical plants. Offshore facilities should refer to API 2RB or other relevant industry standards, though some of the risk assessment principles in API 755-2-2016 can be adapted if proper adjustments are made for marine environments and mobilization logistics.
Q: Does API 755-2-2016 prescribe specific inspection intervals?
A: The standard provides default intervals based on risk categories: High risk (2–5 years), Medium (5–10 years), Low (10+ years). However, it allows for deviation if the operator can justify using a semi-quantitative POF/COF calculation that produces a different interval based on actual damage rates.
A: The standard provides default intervals based on risk categories: High risk (2–5 years), Medium (5–10 years), Low (10+ years). However, it allows for deviation if the operator can justify using a semi-quantitative POF/COF calculation that produces a different interval based on actual damage rates.
Q: Is revalidation mandatory under API 755-2-2016?
A: Yes, the standard requires a full revalidation of the RBI analysis at least every 5 years. Additionally, a partial revalidation must be performed within 6 months of any significant change in process conditions, equipment modifications, or after a near-miss/incident involving the equipment.
A: Yes, the standard requires a full revalidation of the RBI analysis at least every 5 years. Additionally, a partial revalidation must be performed within 6 months of any significant change in process conditions, equipment modifications, or after a near-miss/incident involving the equipment.