Despite steel wastewater tanks and process vessels being critical infrastructure, industry guidance for confirmation of acceptable steel conditions before a maintenance recoat remains limited.

Wastewater tank linings are vital in protecting steel subject to corrosive exposures. As substrates degrade, two remediation paths typically emerge: adequate surface preparation followed by application of an appropriate lining system, or a full repair or replacement of the steel. With no defined inspection language to guide the decision, informed selection becomes difficult.

At best, there is risk of an unnecessary use of time, materials, and funds.

At worst, recoating compromised steel without addressing the underlying damage conceals a problem that may advance to the point of a catastrophic failure.

Case in point: Borrowing inspection language from the oil & gas industry

Badly degraded steel was identified when Carboline experts were asked to provide surface preparation and lining recommendations for two wastewater clarifier tanks in a major Midwestern American city’s treatment plant.

The previous coal tar epoxy lining on the tanks had deteriorated, leaving unprotected steel exposed to corrosive wastewater.

Restoring the clarifiers and then protecting against future corrosion remained top priority, but without understanding the condition of the underlying steel, it was unclear whether a straightforward recoat would be sufficient, or if a more intensive restoration or replacement of sections of steel was warranted.

The search for applicable guidance began with assessing the AWWA D102 – Coating Steel Water-Storage Tanks guidelines. But that standard is confined to potable water tanks, providing no information that could neatly apply to assessing the condition of steel in a wastewater context.

We did find applicable language from American Petroleum Institute’s API Standard 653 – Tank Inspection, Repair, Alteration and Construction. Although developed for steel petroleum tanks, the standard provides a practical framework for evaluating deteriorated steel in continued service without overlapping or conflicting with existing AWWA guidance.

The API 653 emphasis on steel corrosion severity and appropriate steel thickness provided the basis for our surface preparation and material selection guidance that eliminated the risk of coating over steel unsuitable for continued service.

The mutual conclusion between the municipality and Carboline that “good enough” wasn’t good enough was crucial to delivering the specification that was ultimately agreed upon.

Building a tailored protective lining system

Commercial abrasive blasting or SSPC-SP 11 power-tool cleaning are typically sufficient to remove active corrosion and open pit geometry.

But when corrosion results in pitting or section loss beyond acceptable limits, lining performance alone cannot arrest continued deterioration on service-aged steel. API standards state specific guidelines for determining whether to repair or replace steel sections based on thickness level, asset damages, and repair feasibility.

Where deeper pitting or section loss exceeds acceptable limits, mechanical repair—including grinding, weld buildup, or steel replacement—should be completed prior to applying a lining.

If total steel replacement is necessary, the standard outlines that no product will be sufficient in restoring lost sections or compensating for structural degradation. Attempts to do so would be a total loss functionally and financially.

In short, applying API’s standards to steel wastewater storage or process vessels provided us the technical basis for a surface preparation and lining specification we were confident in. Even if this industry crossover isn’t the end of the conversation on assessing steel condition for assets in wastewater service, it’s a great place to start.

For steel exhibiting only light to moderate pitting and retained structural integrity, Reactamine^® 760 is a good fit. The high-performance hybrid polyurethane tolerates uneven surface profiles and features good wetting properties for effective penetration of pits. It is a workhorse lining that provides excellent barrier protection in wastewater immersion service.

Substrates with more severe corrosion or localized section loss may require higher-build technologies like Hydroplate 6500. Its ability to tolerate marginal surface preparation and achieve uniform film characteristics over uneven steel makes it suitable for applications where surface variability persists following surface preparation.

Crucially, both Reactamine 760 and Hydroplate 6500 pass ASTM G210 Severe Wastewater Analysis Tests (SWAT).

Long-lived performance, standard or not

Industry standards matter for critical asset maintenance. But as this case shows, the absence of a standard was not a cause for panic.

This municipality arrived at a repair specification they were confident in because they trusted the technical expertise of a partner with decades of experience across industries.

So often, experience is what lets someone go the extra mile.