Pump station and wet well coatings: concrete and steel in H2S service

Coating a pump station or wet well exposed to H2S takes five things: removing deteriorated concrete down to sound material, repairing and preparing the surface to recognized references, applying a thick lining designed for acid attack, treating steel separately, and organizing the work with bypass pumping and a confined space protocol. Bypass and access often weigh as much as the lining. Induscoat replies to quote requests within 24 business hours.

This guide is for plant maintenance managers, infrastructure managers and buyers who need to rehabilitate a pump station, a wet well, a valve chamber or an industrial effluent lift station in Quebec and Ontario. The attack mechanism is explained in our article on wastewater concrete corrosion and H2S linings; here the focus is on execution and what drives cost.

Why do pump stations deteriorate mostly above the water line?

Because the attack happens where hydrogen sulfide is released and condenses. Drops, turbulence at the inlet and pump agitation release H2S into the air of the well. On the damp walls above the water line and under the cover slab, bacteria turn it into sulfuric acid, which dissolves the cement paste. Permanently submerged concrete generally suffers much less.

Steel lives in the same atmosphere: ladders, pump guide rails, supports, piping, valves, covers and hatches. Microbial corrosion sometimes adds localized attack; our article on microbial corrosion (MIC) describes the signs. A survey of the splash zone, the crown and the steel parts steers the rest of the project.

How should the concrete be prepared before lining?

By removing all weakened concrete, rebuilding the profile, then preparing the surface to recognized references. This step decides adhesion, and therefore service life.

• Removing deteriorated concrete: acid-softened, friable concrete must come off down to sound material. Hydro blasting is often a good fit, because it produces no dust in a confined space and exposes the aggregate without microcracking the substrate.
• Repair: rebuilding sections with a repair mortar compatible with the lining, treating exposed rebar, and crack injection of active or leaking cracks.
• Surface preparation: SSPC-SP 13 / NACE No. 6 covers concrete preparation, and the profile is checked against the CSP chips of the ICRI 310.2R guideline.
• Moisture and contamination: moisture is checked, for example to ASTM D4263, and surface pH is tested. Our article on concrete moisture before epoxy coating details these tests.

In a wet well, concrete is rarely dry. The lining choice must account for residual moisture and water pressure coming from behind the wall.

Which linings hold up in H2S service?

Thick, low-permeability linings resistant to sulfuric acid, chosen for the severity of exposure. NACE SP0892 frames linings over concrete in chemical service.

Common families are high-solids epoxies applied at high build, novolac epoxy for severe acid exposure, vinyl esters, and epoxy or filled mortars that rebuild and protect in one operation. The lining must fill bugholes and voids in the concrete (a surfacer coat is often specified), tolerate substrate moisture and resist abrasion on walls near the inlets. Thickness and number of coats are set by the manufacturer's data sheet and the owner's specification. Our concrete protection page presents the systems, and the final choice is made with our protective coatings service, the reference point for all our work.

How should steel be treated in a wet well?

Separately from the concrete, with abrasive blasting and a system designed for immersion and acidic condensate. Joints between steel and concrete (grouted bases, anchors, penetrations) are the weak points to detail carefully.

Removable parts are often better treated in the shop, with blasting and coating under controlled conditions, while the well itself is rehabilitated. Fixed parts are blasted in place under ventilation. When an element has lost too much section, replacing it with a more resistant material can be better than coating it; that choice is made with the operator.

How do you work while the station stays in service?

With bypass pumping. A pump station generally cannot stop for the time it takes to prepare, line and cure a well.

Bypass means installing temporary pumps and lines that route flow around the well or cell under work, isolating inlets with plugs, then draining and cleaning the structure. In a station with several cells, one cell can be treated at a time. The bypass must be sized for peak flows and monitored continuously, with a contingency plan for rain events or breakdowns. It stays in place for the whole cure. It is often one of the heaviest items in the project, and it is coordinated with the operator; our project management service handles this coordination.

Which confined space rules apply?

Those of the RSST in Quebec and Ontario Regulation 632/05, with CSA Z1006 practices. A wet well is a high-risk confined space because of H2S, oxygen deficiency and solvent vapours during application.

The protocol includes an entry permit, a hazard assessment, continuous gas monitoring, mechanical ventilation, an attendant outside, a rescue plan and retrieval equipment. Lockout of pumps and valves and isolation of inlets are verified before every entry. These measures slow production and must appear in the quote. Quality checks run in parallel: adhesion on concrete to ASTM D7234 and holiday testing of linings on concrete to ASTM D4787. Our coating inspection service can cover these hold points.

What drives the cost of a pump station lining project?

Bypass, access and the depth of concrete repair, more than the lining product. A shallow well with good access and sound concrete under a thin damaged layer is a very different job from a deep, narrow well where the crown has lost a significant thickness of concrete.

The main factors are:

• Bypass: number of temporary pumps, line routing, monitoring and duration.
• Concrete condition: depth of removal, volume of repair mortar, cracks to inject.
• Steel: parts to remove for shop work, parts treated in place, parts to replace.
• Lining system: number of coats, surfacer, reinforcement at inlets.
• Confined space and ventilation: size and number of openings, depth, gas monitoring.
• Season: heating and dehumidification in winter, rain risk during bypass.
• Inspection: hold points, adhesion and holiday testing, final report.

To get an accurate quote, send photos of the crown, walls, inlets and steel parts, the well dimensions, the number of cells, the flow data available and the operator's constraints.

Frequently asked questions

Can a wet well be lined without draining it?

No. The concrete must be cleaned, repaired and prepared dry or nearly dry, which requires draining and bypass. Only some localized emergency repairs are done otherwise.

How long must the station stay on bypass?

For the time of preparation, repair, application and full cure before return to service. The duration is set at quote stage according to the size of the structure, the concrete condition, the system and the season.

Does the concrete need rebuilding before lining?

At a minimum, deteriorated concrete must be removed and lost sections rebuilt. Some filled mortars repair and protect in one operation, depending on exposure severity.

Do you also line basins and clarifiers?

Yes. Our article on water treatment plant coatings covers these structures.

Our crews and qualified subcontractors work from LaSalle, Montreal, across Quebec and Ontario. To line a pump station with our protective coatings service, the price is always on consultation: send photos, wet well dimensions, concrete condition and operating constraints through the request a quote form to get a reply within 24 business hours.