Inspection Strategy

A methodology that uses risk assessment to prioritize and plan inspection activities for pressurized and other equipment. RBI combines Probability of Failure (driven by damage mechanisms and equipment condition) with Consequence of Failure (driven by process hazards and safety impact) to rank equipment by risk and allocate inspection resources where they will have the greatest impact on risk reduction.

The time period between successive inspections of an equipment item, determined by the RBI risk ranking, the remaining life, and applicable code requirements. API 510/570 set maximum intervals but allow extension based on RBI assessments. The inspection interval must not exceed half the remaining life (for general thinning) and should be set at less than half the P-F interval for condition monitoring tasks.

A specific process or phenomenon that causes degradation of material properties, leading to eventual failure of equipment. Damage mechanisms include corrosion (uniform, localized, galvanic), erosion, fatigue, creep, hydrogen damage, stress corrosion cracking, embrittlement, and other metallurgical or environmental attack modes. API 571 catalogues over 60 damage mechanisms relevant to refining and petrochemical equipment.

A group of analysis techniques used to evaluate the condition of materials, components, and assemblies without causing damage or altering their serviceability. NDE methods detect surface and subsurface flaws, measure wall thickness, characterize material properties, and assess the integrity of welds and joints. Common NDE methods include ultrasonic testing (UT), radiographic testing (RT), magnetic particle inspection (MPI/MT), liquid penetrant testing (PT), visual testing (VT), eddy current testing (ECT), and acoustic emission testing (AE).

A qualitative rating of the probability that an inspection activity will correctly identify and characterize the damage present in the inspected equipment. Inspection effectiveness is categorized from A (Highly Effective — high probability of detecting the damage) through E (Ineffective — virtually no chance of detection). The rating depends on the inspection technique used, the skill of the inspector, the coverage area, and the damage mechanism being sought.