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Build an asset integrity programme that connects corrosion threats, inspection findings, maintenance priorities, and major-incident risk.

Asset Integrity for Aging Plants: Corrosion, Inspection and Risk

A storage tank can pass a visual inspection and still contain a thinning floor plate. A pipe can look sound under insulation while chloride stress corrosion attacks the metal. A pressure vessel can remain within its statutory inspection date while a changed operating regime accelerates damage.
Asset integrity management keeps hazardous material inside equipment throughout its intended life. It brings design information, degradation mechanisms, inspection, maintenance, operating limits, and risk decisions into one system.
For an MHI or other high-hazard facility, this work protects the first preventive barrier: containment.

Start with the major-incident scenarios

Many integrity programmes begin with an equipment list. Start one step earlier. Review the HAZOP, BowTie, MHI assessment, and QRA to identify equipment whose failure can cause or worsen a major incident.
This may include:

  • pressure vessels, tanks, reactors, and process piping;
  • relief valves, rupture discs, flare headers, and scrubbers;
  • emergency shutdown valves and remotely operated isolation;
  • firewater pumps, deluge valves, gas detection, and emergency power;
  • instrumented protection systems and critical alarms;
  • bunds, drainage, supports, and passive fire protection.
    Link each item to the hazard scenario and required function. A generic criticality score tells maintenance that a pump matters. A scenario link tells the team that pump failure can disable firewater during an LPG release.
    Our guide to BowTie barrier health explains how to map equipment to preventive and mitigative barriers.

Identify credible degradation mechanisms

Inspection only works when the method can find the damage you expect.
For each equipment class, consider:

  • general and local corrosion;
  • corrosion under insulation;
  • erosion, vibration, and fatigue;
  • cracking from stress, hydrogen, chloride, or caustic service;
  • high-temperature damage and creep;
  • embrittlement, ageing seals, and polymer degradation;
  • settlement, foundation movement, and support failure;
  • fouling, blockage, coating breakdown, and loss of fireproofing.
    Use process chemistry, temperature, pressure, materials, contaminants, past findings, and failure history to select credible mechanisms. A thickness survey will not give adequate assurance for every cracking mechanism.

Define integrity operating windows

Equipment life depends on how the plant runs it. Define limits that protect the material and the safeguard function, then monitor excursions.
Examples include:

  • maximum temperature to prevent accelerated corrosion or creep;
  • minimum flow to avoid dead legs and deposition;
  • water, oxygen, chloride, sulphur, or pH limits;
  • vibration and bearing-temperature limits;
  • maximum duration for a bypassed or impaired protective system.
    When operations exceed an integrity limit, require technical review. Repeated excursions can invalidate inspection intervals and remaining-life estimates. Route changes to operating envelopes through Management of Change.

Build a risk-based inspection plan

Risk-based inspection combines the likelihood of failure with the consequence of failure. It helps the facility put specialist inspection effort where loss of containment would cause the most harm.
A defensible plan records:

  1. equipment and circuit boundaries;
  2. credible damage mechanisms;
  3. consequence and likelihood basis;
  4. inspection method, location, extent, and interval;
  5. acceptance criteria and responsible competent person;
  6. action rules for defects, overdue work, and changed service.
    Do not use risk-based inspection to stretch intervals without evidence. The method should improve knowledge and targeting, not hide a maintenance backlog.

Turn inspection data into decisions

An inspection report needs a decision owner. Define how the team will:

  • compare results with minimum allowable thickness or fitness-for-service criteria;
  • calculate corrosion rates and remaining life;
  • investigate unexpected or accelerating damage;
  • repair, replace, derate, monitor, or temporarily control the equipment;
  • update drawings, data files, inspection locations, and future intervals;
  • review whether similar equipment carries the same defect.
    Record the technical basis for continued operation. "Monitor condition" needs a measurement, frequency, limit, and person who acts when the limit is reached.

Control overdue inspections and maintenance

High-hazard sites often carry overdue work because access is difficult or shutdown windows move. Treat deferral as a risk decision.
Before extending an interval, review:

  • the equipment's barrier function and failure consequence;
  • past inspection results and data quality;
  • current operating conditions and excursions;
  • degradation rate and remaining-life uncertainty;
  • temporary controls, monitoring, and revised due date;
  • approval from competent engineering and operations personnel.
    Track overdue work on safety-critical equipment separately from routine backlog. Senior leaders need visibility of impaired barriers, not one combined maintenance percentage.

Aging plant includes people and information

Equipment ages alongside drawings, procedures, software, and workforce knowledge. Retiring specialists can take failure history and inspection judgment with them. Old drawings may not reflect decades of modifications.
Use walkdowns, structured handovers, equipment histories, photographs, damage maps, and mentoring to retain knowledge. Reconcile the plant with P&IDs during PHA revalidation and major shutdown planning.

Connect integrity to the MHI risk picture

The frequency assumptions in a QRA rely on containment and protection systems remaining fit for service. A corroded pipe, unavailable deluge valve, or overdue relief test can change the risk even if the original model remains untouched.
Review the risk assessment when:

  • inspection finds an unexpected widespread mechanism;
  • equipment operates outside its design basis;
  • a critical safeguard remains impaired;
  • the plant extends service beyond design life;
  • incidents or near misses challenge failure-frequency assumptions.
    The Department of Employment and Labour's March 2026 MHI workshop focused on plants being fit for purpose and on tools for monitoring sector performance. Integrity records give duty holders evidence that the controls described in their safety documentation exist in the field.
    MMRisk supports hazard studies, barrier reviews, MHI risk assessments, and process-safety audits that connect integrity findings to major-incident risk. Contact our team when inspection results affect a critical scenario or operating decision.

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