A pipe rack is repainted by treating the supports first, where the pipe rests on the beam: water stays trapped there and crevice corrosion thins the pipe out of sight. Lines are lifted or the work is done in sections to prepare and coat those areas, isolating pads are added, then an ISO 12944 system suited to the corrosivity category is applied. When the process keeps running, preparation is done with power tools or low-emission methods, under a work permit.
Pipe racks carry steam, water, compressed air and product lines between the units of a plant, refinery or mining complex. They are long, high, congested and almost always in service. This guide helps maintenance managers and project managers in Quebec and Ontario prepare a repainting program that treats corrosion where it actually does damage. It complements our steel structure painting service.
Where does a pipe rack corrode first?
It corrodes first at the contact points between pipes and their supports, then at structural connections and horizontal surfaces that hold water and deposits. The rest of the structure, better drained, often holds up much longer.
Areas to watch:
- Pipe-to-beam supports. The pipe rests directly on the beam flange, or on a shoe, and the gap holds water, dust and salts. This is where crevice corrosion develops, producing localized wall loss under the bearing point.
- U-bolts and clamps. They pinch the pipe, wear the coating through thermal movement and create an additional crevice.
- Bolted connections and gussets. Corners and bolts hold moisture.
- Top flanges of beams. Process deposits, leaks and snow accumulate there.
- Insulated piping. Corrosion under insulation advances where jacketing is damaged; see our article on corrosion under insulation.
A survey of these areas, backed by photos and thickness readings, separates what gets repainted from what gets repaired first. The survey also records which lines are hot, which carry flammable or toxic products, and which can be isolated during a shutdown, because those facts shape the preparation method and the work sequence more than the condition of the paint itself.
How should pipe-to-support contact points be treated?
Treat supports by making the contact area accessible, preparing and coating it like the rest of the pipe, then eliminating the crevice that held water. Painting around a support without lifting the pipe leaves the most corroded area untouched.
| Step | Usual method | Checkpoint |
|---|---|---|
| Access to the contact area | Local lifting of the pipe by jack or hoist, one line at a time, per a procedure approved by the operator | Allowable load and stress on the line |
| Assessment | Thickness reading under the former support | Decision: coat, reinforce or replace the section |
| Preparation | Power tools to the required grade, or local blasting | Grade achieved inside the crevice, not only around it |
| Coating | System compatible with the line's system, controlled thickness | Continuity around the full contact circumference |
| Crevice elimination | Non-metallic isolating pad, half-round support or bonded wear plate | Material compatible with service temperature |
Pipe coating relies on the same principles, whether the line is on a rack or at grade.
How is steel prepared while the process keeps running?
Steel is prepared with methods compatible with in-service equipment and site rules: power tools per SSPC-SP 3, SP 11 or SP 15, contained local blasting, or low-dust methods. The choice is made with the operator, because it affects process safety.
Typical constraints on a live rack:
- Work permits. Spark-producing tools often fall under hot work and require atmosphere monitoring, especially near flammable product lines.
- Equipment protection. Valves, instruments, flange gaskets, cables and insulation are protected before preparation.
- Hot lines. Surface temperature decides which product can be applied; some lines are only treated during a shutdown.
- Dust and waste. Containment, vacuum collection and waste recovery, especially if the old paint contains lead.
Power tool grades are detailed in our article on power tool cleaning SSPC-SP 3, SP 11 and SP 15, and dust control in our guide to blasting in operating plants.
How is access organized on a rack?
Access is organized by height, rack width, traffic underneath and the number of pipe levels. Access is often a major share of the effort; it is planned before the system is chosen, because it sets the duration and sequence of the work.
Common options:
- Aerial work platforms. Efficient when the ground is clear and load-bearing and traffic can be detoured.
- Scaffolding. Needed for long jobs, multiple levels or confined areas; it also supports containment.
- Access from the rack walkway. Possible for some light work, with fall protection.
- Work in sections. The rack is divided into sections that are fully completed (access, preparation, coating, inspection) before moving to the next.
Traffic lanes under the rack, cable trays and neighbouring lines are protected for the duration of the work.
Which ISO 12944 system suits a pipe rack?
The system is chosen from the site's corrosivity category, defined per ISO 12944-2, the target durability and the achievable preparation grade. ISO 12944-5 gives typical systems for each combination; each product's data sheet sets thicknesses.
| Situation | Generally selected category | System direction |
|---|---|---|
| Indoor rack, dry atmosphere | C2 or C3 | Epoxy or two-coat system depending on target durability |
| Outdoor rack, moderate industrial environment | C3 or C4 | Zinc-rich or epoxy primer, epoxy intermediate, polyurethane topcoat |
| Rack exposed to fumes or splash | C4 or C5 | Thick high-durability system, reinforced detailing at supports |
| Preparation limited to power tools | Depends on site | Surface-tolerant primer compatible with the achieved grade |
Zinc-rich primer needs high-grade preparation; if blasting is not possible, a surface-tolerant primer is chosen. Our article on ISO 12944 explains the categories, and our guide to C3, C4 and C5 paint systems gives examples. The system is part of our industrial protective coatings.
How is quality checked on a rack?
Quality is checked through hold points, zone by zone: preparation grade before application, ambient conditions, thickness of each coat, adhesion when recoating an old system. Supports and connections are checked separately, because they decide how long the job lasts.
- Thickness. Readings per SSPC-PA 2 or ISO 19840, as specified, with attention to edges and bolts.
- Adhesion. Testing by the specified method when recoating over an old coating.
- Supports. Photo and record per treated support: thickness measured, repair done, pad installed.
- Log. Annotated rack plan showing treated areas, useful for the next maintenance cycle.
Our article on maintenance painting of steel structures explains how to choose between touch-up, partial repainting and full repainting.
How to get a quote?
Our crews and qualified subcontractors work from LaSalle, including Montérégie and Hamilton, on pipe racks in service or during shutdowns. Send the plan or photos of the rack, its length and height, the lines in service, their temperatures and site constraints through the request a quote form: pricing on consultation, reply within 24 business hours.
Frequently asked questions
Why do pipes rust mostly at their supports?
Because the gap between pipe and support holds water and deposits, and the coating there is worn by thermal movement. The crevice corrosion that develops is localized and often invisible until the pipe is lifted.
Does the process have to stop to repaint a rack?
Not always. The structure and most lines are treated while running, with suitable preparation methods and work permits. Hot lines or areas where hot work is prohibited may wait for a shutdown.
Are isolating pads enough to stop corrosion at supports?
They eliminate metal-to-metal contact and reduce water retention, but they do not protect a pipe that is already corroded. The contact area is prepared and coated first, then the pad is installed.
Can a zinc-rich primer be applied without blasting?
Generally not. Zinc-rich primers need high-grade blasting to ensure contact between the zinc and the steel. When only power tool preparation is possible, a surface-tolerant primer is selected.
Hicham M, P Eng, PMP
Engineer and project manager (PMP) at Induscoat. Over 16 years of experience in industrial coatings, composite repairs and wear protection on mining, energy and petrochemical sites in Canada and internationally.