Process plant inspection: seeing equipment that cannot stop, without scaffolding

Plant deterioration falls into metal loss (external corrosion, corrosion under insulation (CUI), internal wall thinning), heat and pressure damage (creep, thermal fatigue, refractory breakdown) and structural deterioration (corroded steel frames, spalled fireproofing, cracked foundations). All of them advance where rainwater, salt, thermal cycling and repeated operation meet.

Japanese plants fall under several laws depending on what they handle: the High Pressure Gas Safety Act (safety inspections and periodic self-inspections of gas equipment), the Fire Service Act (hazardous materials facilities and tanks), the Industrial Safety and Health Act (performance inspection of boilers and pressure vessels), and for large complexes the Act on the Prevention of Disasters in Petroleum Industrial Complexes. Much of the inspection is timed to turnarounds, planned shutdowns every few years.

The means of access become the cost and the length of the outage. Tall columns and flares need scaffolding, rope access or aerial lifts. Vessel interiors must be shut down, cooled, purged and gas-tested before anyone enters. Scaffolding often takes a large share of turnaround cost.

The other pain is people. Many Japanese plants were built during the high-growth era and are ageing, while veteran engineers keep retiring. Fewer people must inspect more equipment in shorter outages.

Drone use in plants splits into looking at the outside while running and looking inside during shutdowns. Imaging a live flare tip is something only drones can easily do.

In Japan, a trial flew drones inside an idle heavy-oil tank to see whether imagery could replace the legally required visual inspection. The finding: drones work for first-pass screening of corrosion and scale but cannot replace quantitative assessment such as depth. Scouting and narrowing down during a shutdown is where they sit today.

A plant is one of the most demanding places for a drone: areas where flammable gas may be present, hot equipment, spaces surrounded by steel, and GNSS-dead vessel interiors. Miss any one and the accident will not stop at the aircraft.

• Explosive atmospheres: off-the-shelf drones are not explosion-proof. In hazardous areas, fly only when the unit is shut down and gas-free, or from outside the zone. Certified explosion-proof drones remain rare worldwide. Explosive atmospheres
• Heat: flares, furnaces and stacks radiate heat and send hot exhaust upward. Keep distance and zoom in; watch the aircraft’s temperature. Heat
• GNSS-denied: inside vessels and columns and under pipe racks there is no GNSS. Choose aircraft that localise with cameras or LiDAR. GNSS-denied environments
• Confined spaces: vessels and manholes are cramped and dark. You need caged, collision-tolerant drones and lighting. Confined spaces
• Magnetic disturbance: compasses lie near steel columns and frames. Be ready to fly in modes that do not rely on magnetic heading. Magnetic disturbance

Images are useful only once they connect to the equipment register and inspection plan. If you cannot tell which column, at what elevation and facing which direction a photo shows, you cannot compare it with last time or decide where to inspect next.

In March 2019 Japan’s METI, the Fire and Disaster Management Agency and the Ministry of Health, Labour and Welfare, through their joint liaison conference, issued guidelines for the safe operation of drones in plants, revised as version 2.0 in March 2020. They set out conditions for using drones in hazardous areas and safety measures near operating equipment. How far drone imagery can count toward statutory inspection depends on the inspection type and the competent authority, so check beforehand.

Abroad, the US OSHA Process Safety Management (PSM) standard requires mechanical integrity inspection, typically carried out to industry codes such as API 510 (pressure vessels), API 570 (piping) and API 653 (tanks). Regimes such as the UK’s COMAH cover major-hazard sites. Explosion-proof equipment is certified under the EU’s ATEX or the international IECEx scheme.

Flight rules apply separately. Outdoor plant areas fall under aviation law, and flights within 30 m of people or property need permission or approval. Fully enclosed indoor spaces are generally outside the aviation rules, but buildings with large openings need judgement. Compare countries in world regulations.

• Under insulation: CUI can only be found by removing insulation or by other NDT (radiography, guided waves and so on). Thermal images give clues, not answers.
• Quantitative assessment: corrosion depth and wall thickness cannot be measured from photos. Contact ultrasonic drones exist but cannot reach everywhere.
• Flying in live hazardous areas: never fly an ordinary drone where flammable gas may be present.
• Eliminating human entry: people will still need to go in for final checks and repairs.
• Rating and accountability: judging remaining life and whether to keep running belongs to the person responsible for the equipment.

In a corner of the petrochemical complex sits a drone in an explosion-protected dock. Every morning it traces the columns and frames on a fixed route, images the flare tip, logs insulation hot spots and returns. Before each turnaround it scouts the vessel interiors and produces a list of where scaffolding is actually needed. That is the picture our editors expect.

People climb only where it is worth confirming. They read corrosion rates, set operating limits and plan the next turnaround. Inspection shifts from entering dangerous places to caring for the whole life of the plant.