Case Study Overview

Site Power plant
Location Thailand
Repair Type Corrosion protection
Defect Heavily corroded metalwork and parts inside heat exchanger water box

Repair Products

Liquid Metal Epoxy Coating

Case Study PDF

Case Study Details

A water box – also known as a plenum chamber – is found at the end of a heat exchanger. It supplies and directs the flow of water through the tubes of the heat exchanger.

Conditions inside a water box are perfect for galvanic corrosion and cavitation. Extreme temperatures, high pressure and unpurified water passing through the chamber leave the metalwork under constant attack and requiring frequent repair.

The power plant had spent many years using a standard epoxy coating to protect the water box. The rate of corrosion meant a new coating had to be applied annually.

This involved shutting down the system, disassembling the heat exchanger, applying the coating and then putting it all back together. It was a disruptive process which resulted in significant downtime for the plant.

It was therefore decided to find a more robust, effective coating to protect the water box which did not require yearly reapplication. The plant analysed conditions inside the chamber and came up with a specification for their ideal epoxy coating.

Temperature resistance had to be as a high as 149°C with long-term performance at operational temperatures of 25–40°C. It needed to be resistant to pH 8-10 and pressure up to 3 bar. Most importantly, the plant wanted a coating strong enough to last several years at least.

Taking these requirements into consideration, Sylmasta recommended using Liquid Metal Epoxy Coating to protect the inside of the water box, the tubes within the water box and its condenser faceplate.

Liquid Metal is metal-filled, meaning it offers superior corrosion resistance and enhanced durability by creating a thicker, more resilient layer. The cured material has Shore D hardness in excess of 80 and a maximum service temperature of 150°C.

Before application, the metal surface was thoroughly cleaned to remove rust, other contaminants and any traces of the previously applied standard epoxy coatings.

Liquid Metal was then painted onto the areas requiring protection using a brush. Three coatings 1mm thick were applied. Liquid Metal has a 90-minute gel and a four hour re-coat time. The entire repair was completed over two days.

Once the final coating had cured, the original metalwork inside the heat exchanger water box, tubes and the condenser faceplate were covered with a 3mm thick metallic layer, offering ultimate protection against corrosion and cavitation.

Six months after the repair, the manager of the engineering company responsible for maintenance at the plant contacted Sylmasta with an update.

“I had a good experience with Liquid Metal. We have looked at the heat exchanger and condenser again and the coating has fully performed and protected from corrosion very well.”

“We now want to use Liquid Metal on 22 blowdown tanks at this plant and more systems at other power plants in Thailand where we run maintenance.”

Products Used

Liquid Metal
Coating brush applied to create a metallic layer which protects against corrosion

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