The growing use of hydrojetting in ship repair is increasing demand for coating systems capable of protecting steel surfaces that can be challenging for conventional two-component paints, according to German steel protection specialist Steelpaint.
Hydrojetting, also known as water jetting or water blasting, uses ultra-high-pressure water, typically at 700–1,000 bar, to clean, descale and remove existing coatings from ship hulls, decks, cargo holds and tanks. The process is increasingly being used as an alternative to dry abrasive blasting during drydock maintenance, amid greater scrutiny of the environmental impact of spent abrasive and contaminated waste.
Unlike abrasive blasting, hydrojetting produces no dust or spent abrasive and can reduce the amount of contaminated waste generated during surface preparation. However, the process presents challenges for conventional coating systems because it does not create a new anchor profile on the steel surface. Residual moisture and flash rust can also affect coating adhesion and curing.
“These conditions can make it difficult for traditional coatings to perform reliably, particularly in hot and humid climates where relative humidity can exceed recommended application limits. If conditions are not ideal, such coatings can fail to adhere properly, blister, crack or break down,” has stated Andreas Engert, technical director at Steelpaint.
Single-component moisture-cure polyurethane coatings can offer an alternative in these conditions. The company cites its Stelpant and Stelcatec systems as examples of coatings designed to tolerate high humidity and damp substrates.
According to the company, the coatings can be applied at relative humidity levels of up to 98% without dew-point restrictions and can be used on damp steel and surfaces showing light to medium flash rust. They are also designed to maintain adhesion on partially corroded or relatively smooth steel.
“The coatings are intended in particular for onboard maintenance applications, where conventional surface-preparation requirements may be difficult to achieve. They require no mixing and can be applied by brush, roller or spray to damp or manually prepared steel,” has added Andreas Engert.
The systems can be used at temperatures ranging from -5°C to 50°C and at relative humidity levels of up to 98%. The company also says they adhere to stainless steel, galvanised steel and aluminium, allowing corrosion-protection work to be carried out during drydocking or while vessels remain in service.
The coatings can be applied to hydrojetted steel prepared to SSPC-SP WJ/NACE WJ standards, including WJ-3 to WJ-2, as well as to vapour-blasted and manually or power-tool prepared surfaces. Hydrojetting has gained particular acceptance where waste-disposal requirements, environmental controls or operational constraints make abrasive blasting less practical.
“By combining hydrojetting with moisture-cure coating technology, shipowners and offshore operators benefit from an alternative corrosion-protection method that can simplify maintenance, reduce maintenance costs and extend service life in demanding conditions,” Frank Müller, Director of Steelpaint.
The single-component nature of the coatings can further reduce material waste and packaging requirements. Unlike conventional two-component systems, they do not require mixing and have no limited pot life, reducing the amount of unused mixed coating that must be discarded.
Lastly, the combination of hydrojetting and moisture-cure coatings therefore offers potential benefits in terms of environmental impact, labour requirements and material efficiency, alongside corrosion protection in demanding marine environments.