Repainting a pressurized propane or ammonia tank means preparing and protecting the shell without affecting its integrity: preparation suited to the site, a light reflective finish, careful inspection of the saddles and wear pads where water collects, and work carried out under the site's permits and gas detection. Any repair to the shell falls under the pressure vessel code, not under the painting contractor.
Propane tanks at plants, farms and distributors, and ammonia tanks at industrial refrigeration facilities and agricultural sites, sit outdoors all year. Paint plays a double role there: it protects the steel from corrosion and limits solar heating of the contents. This guide is written for maintenance and process safety managers in Quebec and Ontario. It complements our tank and water tower painting page.
Which rules govern painting a pressure tank?
Two families of rules apply: the pressure vessel code, CSA B51, which covers the design, registration, inspection and repair of the shell, and the installation code for the product, such as CSA B149.2 for propane storage and handling. Requirements from the owner, the gas supplier and the insurer are added to these.
What this changes for painting:
- The shell is not an ordinary substrate. No grinding beyond what preparation requires, no welding, and no fitting removed without authorization.
- Findings go to the inspector. Pitting, thinning, cracks or deformation found during preparation are reported to the owner, who brings in the vessel inspector.
- Metal repairs belong to an authorized organization and the provincial authority having jurisdiction, under CSA B51.
- Regulatory markings (nameplate, product identification, hazard symbols) stay legible or are reapplied exactly.
For the logic of in-service vessel inspection, our article on API 510 offers a useful framework.
Why use a light, reflective colour?
Because a light shell absorbs less solar radiation, which limits heating of the liquefied gas and the pressure rise that comes with it. Installation codes and supplier requirements generally call for a light finish; the applicable requirement is checked before choosing the colour.
In practice:
- Polyurethane or polysiloxane topcoat with good colour and gloss retention, so the surface stays reflective over time.
- Keeping it clean. A dirty or chalked surface reflects less; periodic washing is part of maintenance.
- Contrasting markings. Product identification and hazard symbols applied over the light finish, per the requirements in force; our article on safety colours and marking covers the principles.
The complete system (primer, intermediate, topcoat) is selected for site corrosivity, as for any steel structure; it is part of our protective coatings.
Where does corrosion hide on a pressure tank?
It hides mostly where water collects and where nobody looks: under saddles and wear pads, along the bottom of the shell, around nozzles and under insulation where there is any. The table summarizes the zones to inspect.
| Zone | What to look for | Usual treatment |
|---|---|---|
| Saddle and wear pad interface | Pack rust, swelling, trapped water | Edge preparation, crevice sealing, reporting if corrosion advances under the plate |
| Bottom of the shell | Corrosion from condensation and splash | Careful preparation, full system thickness |
| Nozzles, flanges and relief valve supports | Crevice corrosion, attacked bolting | Power tool cleaning, bolting protection |
| Shell welds | Rust along beads, visible cracks | Report to the inspector before any painting |
| Under insulation (refrigerated tanks) | Corrosion under insulation | Insulation removed by zones, suitable system, insulation jacket restored |
For insulated ammonia tanks, our guide to corrosion under insulation details the inspections.
How is corrosion under saddles and wear pads treated?
It is treated by clearing and preparing the edges of the interface, assessing with the inspector how far the corrosion goes, then closing the crevice so water no longer gets in. A coat of paint over a rusted interface only hides the problem.
The gap between the saddle, the wear pad and the shell creates classic crevice corrosion, explained in our article on crevice corrosion. The steps:
- Inspection. Locate pack rust swelling and rust streaks, measure thickness around the area if the inspector requests it.
- Edge preparation. Remove accessible rust by power tool cleaning or local blasting.
- Decision. If corrosion runs deep under the pad, the owner and the inspector decide on further examination or a controlled lift; this is not a painting crew decision.
- Sealing. Penetrating product, then a compatible sealant to close the crevice, before the paint system.
- Follow-up. Photos and reference marks for comparison at the next inspection cycle.
On an ammonia tank, monitoring welds and high-stress areas matters even more because carbon steel can suffer stress corrosion cracking there.
How do crews work safely next to an installation in service?
Work proceeds under the site permit system, with continuous gas detection, no unauthorized ignition source, protection of relief valves, gauges and piping, and an emergency plan known to everyone. Propane is flammable, ammonia is toxic and can also burn: each product dictates its own measures.
Usual measures:
- Work permits. Cold or hot work depending on the preparation method, issued by the site after a hazard analysis.
- Gas detection. Portable detectors for propane (explosive limit) and ammonia (toxicity), with stop thresholds known to crews.
- Spark and static control. Grounding of blasting equipment, electrical equipment suited to the area, and a preparation method that limits sparks when required.
- Fitting protection. Relief valves, vents, level gauges, pressure gauges and nameplates masked; never paint over a relief valve outlet.
- Protective equipment. Respiratory protection and escape respirators suited to ammonia when the site requires them.
- Coordination. No product transfer during certain phases, as decided by the operator.
Abrasive blasting is not always allowed nearby; power tool cleaning or hydro blasting are then reviewed with the site.
How does a typical repainting project run?
It runs in sequence: site visit and assessment with the operator, work plan and permits, preparation, inspection of critical zones, system application, inspection, then markings and records handed over. Repainting frequency is aligned with the vessel's periodic inspections.
Aligning the two saves time and gives better information: the inspector sees the bare shell during preparation, and the painting crew knows before starting which areas need a decision. When several tanks share a site, they are often treated in sequence so that only one is surrounded by work at a time, which keeps permits, gas detection and access simpler for the operator.
- Before. Assessment of paint condition, identification of risk zones, preparation method chosen to suit site constraints.
- During. Ambient conditions measured, thicknesses checked, findings passed on as they arise.
- After. Markings reapplied, work record (preparation, products, thicknesses, photos) handed to the owner.
Our coating inspection service can produce the initial assessment and the final check. For maintenance of neighbouring structures, see our article on maintenance painting of steel structures.
Where do we work and how do you get a quote?
Our crews and qualified subcontractors work from LaSalle across Quebec and Ontario, including Drummondville and Ontario, on industrial, agricultural and refrigeration tanks.
Pricing is on consultation: it depends on the number and size of tanks, paint condition, the preparation method allowed on site, the areas to treat under saddles, safety requirements and the work window. Send photos, dimensions and the stored product through the quote request: reply within 24 business hours.
Frequently asked questions
Does the tank have to be emptied for repainting?
Not necessarily. External painting is often done with the tank in service, under permit and with gas detection. The owner decides based on the preparation method, shell condition and the site hazard analysis.
Can a propane tank be painted a colour other than white?
It depends on the requirements that apply to the site and the supplier. A light reflective colour is generally required; the requirement is checked before choosing.
What if deep pitting is found during preparation?
Work stops on that area, it is marked and the owner is informed, who has the vessel inspector assess the pit. The painting crew does not fill it without a decision.
Does the external coating protect against ammonia cracking?
No. Stress corrosion cracking in ammonia service is managed through design, product control and inspection. Paint protects only the external surface.
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.