Pulp and paper mill coatings: what to apply and where

In a pulp and paper mill, coatings are chosen area by area: an epoxy and polyurethane system designed for condensation on machine room structures, high chemical resistance linings (novolac epoxy or vinyl ester, per the manufacturer's resistance tables) for bleaching and liquors, and systems suited to moisture and thermal shock on concrete. The annual shutdown is used to complete the areas that cannot be reached during operation, provided everything has been prepared beforehand.

Few plants combine so many attacks on one site: constant hot humidity, condensation on framing, chlorinated compounds, hot alkaline liquors, sulfur compounds, effluents and concrete floors exposed to spills and hot water. A standard paint system that performs well in a warehouse blisters or peels quickly here. This guide is for maintenance, reliability and project managers at mills in Quebec and Ontario who are planning an industrial painting or coating campaign.

What attacks do coatings face in a pulp and paper mill?

There are four families of attack: humidity and condensation, oxidizing chlorinated chemicals, alkaline and sulfur-bearing liquors, and mechanical and thermal stress. They often overlap on the same equipment, which means identifying them one by one before choosing.

The concentration and temperature limits for each product cannot be guessed: they are checked in the manufacturer's chemical resistance tables and written into the specification. The same goes for upset conditions: a tank that normally holds a dilute product but occasionally receives a hotter or more concentrated stream has to be lined for the worst case, not the average.

How are machine room structures protected?

Machine room structures are protected with a system designed for condensation and high-grade preparation, because the steel stays hot and damp almost all the time. The corrosivity category is set per ISO 12944-2 from actual conditions rather than from the building's generic category.

• Roof framing and purlins. Condensation forms continuously; a thick epoxy system, possibly over a zinc-rich primer, with a suitable topcoat, is the usual basis.
• Walkways, handrails and supports. Exposed to splash and washdown; edges and welds receive a stripe coat.
• Hoods and ducts. High heat and humidity; service temperature limits the choice of products.

Our article on ISO 12944 C3, C4 and C5 paint systems shows how to move from category to system. A particular watch point: spraying paint above a running machine can contaminate the sheet; containment and machine protection are planned with operations.

Which linings for tanks, chests and towers?

For tanks, the choice starts with the stored product, its concentration and its temperature, then abrasion and the cleaning method. Hot alkaline liquors, bleaching chemicals and stock do not call for the same systems.

• Alkaline liquors. Novolac epoxies and some alkali-resistant systems are often considered; temperature resistance is checked product by product.
• Chlorinated chemicals and acids. Vinyl esters are frequently selected in oxidizing service; our comparison of vinyl ester vs novolac epoxy details the differences.
• Stock chests. Abrasion and high-pressure cleaning point to thick, tough linings, sometimes to a rubber lining.

The full selection approach is described in our guide to industrial tank lining selection. This work falls under our protective coatings, our core business.

How are concrete floors and structures treated?

Concrete is treated by first checking its moisture, contamination and condition, then choosing a system that tolerates spills, hot water and thermal shock. In a pulp and paper mill, concrete is often saturated with moisture and soaked with chemicals.

• Preparation. Removal of contaminated or degraded concrete, mechanical preparation per SSPC-SP 13 / NACE 6, defect repair.
• Moisture. Measured per ASTM F2170 or the specified method; see our article on concrete moisture before epoxy coating.
• System. Epoxy or vinyl ester mortar, urethane cement for thermal shock, membranes in trenches and sumps; the choice follows the product, temperature and traffic.

The concrete protection page presents protection systems for concrete structures.

How are surfaces contaminated with fibres and chemicals prepared?

Preparation starts with washing, then blasting, then a cleanliness check: a surface covered with fibres, liquor deposits or salts will not hold any coating, even after what looks like a blast. Contamination has to be removed, not covered.

• Washing and degreasing. Per SSPC-SP 1 for oils and grease, then water washing for soluble deposits.
• Blasting. Abrasive blasting to the grade set by the specification, or SSPC-SP 3, SP 11 or SP 15 power tool cleaning when blasting is not possible during operation.
• Salts and contaminants. Soluble salt checks per ISO 8502-6 and ISO 8502-9 on surfaces exposed to chlorinated chemicals.
• Dust. Blasting in an operating plant requires containment and dust management, as explained in our article on blasting in operating plants.

How do you make the most of the annual shutdown?

You make the most of the annual shutdown by reserving its hours for areas that cannot be reached during operation, and completing everything possible beforehand: surveys, tests, procurement, scaffolding, permits. The shutdown is short and costly; it should not be the moment you discover the condition of the surfaces.

• Before the shutdown. Inspection and survey of the areas, adhesion tests on existing coatings, system selection, product orders, lifting and access plan.
• During the shutdown. Cooling, ventilation and humidity control of tanks, dehumidification if needed, blasting and application to a tight sequence.
• Cure. Time before return to service is read from the data sheet; heat-accelerated curing can be planned.
• Coordination. Coating work fits into the overall shutdown scope; our project management service handles that coordination.

Our article on planning coating work in a plant shutdown details this sequencing.

Which checks prevent failures?

Checks are required at every stage, because most failures in pulp and paper mills come from inadequate preparation or application outside the planned conditions. The same checks then form the asset's record.

• Ambient conditions. Surface temperature, relative humidity and dew point, measured and recorded.
• Thickness. Dry film thickness per SSPC-PA 2 on steel.
• Adhesion. Pull-off testing per ASTM D4541 on steel or ASTM D7234 on concrete, when the specification calls for it.
• Holidays. Holiday testing per NACE SP0188 for immersion linings.

Our article on coating failure modes helps interpret existing blistering or peeling.

How do you get a quote for your mill?

Describe the target areas, the chemicals in contact, temperatures, current condition and shutdown length. Pricing is on consultation: it depends on access, preparation, containment, systems and the shutdown window. Our crews and qualified subcontractors work in particular in Saguenay-Lac-Saint-Jean and in Mauricie and Centre-du-Québec. For our industrial painting service, send photos and surveys through the request a quote form: reply within 24 business hours.

Frequently asked questions

Can a machine room be painted during production?

Yes, for part of the work, with power tool preparation, containment and moisture-tolerant products. Areas above the machine or very hot areas are better handled during the annual shutdown.

Why does paint blister on damp framing?

Most often because of salts or contaminants left under the film, application below dew point or a system not designed for condensation. Diagnosis always comes before repainting.

Is vinyl ester suitable for every liquor?

No. Its resistance depends on the product, concentration and temperature. In some hot alkaline services another system is preferable; the manufacturer's resistance tables decide.

Does a tank have to be fully relined at every shutdown?

No. An inspection often allows the work to be limited to localized repairs. Full relining is decided when defects are widespread or adhesion is no longer assured.