Corroded contaminated metals: what’s the solution? By Levente Bazsanyi
One of the major challenges faced by maintenance engineers across many industries is the extremely limited amount of time in which an urgent repair, such as a pipe or tank leak, must be carried out. In the real world, when a rapid repair is required, ideal surface preparation is not always an option. However, many available polymer repair solutions are not compatible with minimal surface preparation, and therefore, can often lead to failure. This article focuses on the latest epoxy technology of a new two-component paste grade material which achieves a quick, durable repair also in oil contaminated, cold, wet and underwater areas. This cold curing system achieves excellent adhesion to manually prepared substrates where grit blasting is not possible. Due to its low temperature cure and capability of being applied underwater, this product is ideal for the long-term repair of offshore structures, splash zones and marine vessels.
Producing faster curing epoxy materials and those curing at lower temperatures have long been goals of protective coatings and repair composites manufacturers. Improved production rates, reduced time, as well as the ability to apply materials at lower temperatures and extend equipment life are attractive benefits to the coating supplier, applicator, end-user and owner alike.
A critical aspect of any coating or repair material is its ability to adhere to the substrate. Common standards for coatings and repair materials require at least a 75 micron angular profile and SA 2.5/NACE No. 2 /SSPC-SP 10 near white metal surface cleanliness. In addition, it is critical that the substrate be clean, dry and free of any contaminants. Unfortunately, meeting all these requirements in the field can often be difficult, if not impossible.
New technology in polymeric materials has led to the development of an epoxy-based paste grade product that can be applied onto oily, wet and even underwater surfaces, which eases some of the typical surface preparation requirements. This material is effective at displacing contaminants from the substrate via a strong electronic affinity with the metallic substrate, which allows the epoxy to penetrate the profile and create a strong mechanical bond even without grit-blasting. Surfaces only need to be prepared to SSPC-SP 11 (power tool cleaning to bare metal).
Alternative solutions and their limitations
Adhesives currently available on the market do not tend to perform well when bonding to oil-contaminated surfaces and substrates in wet or aquatic environments, especially at low temperatures. Commercial surface-tolerant bonding adhesives are slow to cure and have relatively low bond strengths compared to adhesives formulated for dry applications. Traditional acrylic adhesives have longer set times that slow assembly processes and lower impact resistance, resulting in brittle bonds. These materials also have a limited shelf life and high odour levels that can cause Health and Safety concerns.
Adhesives fall short for use in adverse conditions for a variety of reasons. In two-component adhesive systems, the chemically reactive components needed for curing generally react low in the presence of water and oil and create poor quality bonds. Light curable adhesives generally require external energy sources; this makes them less desirable from a logistical standpoint. Few thermally cured adhesives result in rapid, high-strength adhesion, and even fewer function in high-moisture environments. Moisture reduces adhesion and low water temperatures reduce exothermic cure for underwater adhesives. As a result, underwater adhesives either cure poorly or require long cure times to obtain sufficient adhesive properties.
Latest technology development
Several market-driven requirements have been identified for a fast curing product with surface tolerance. There are instances where surface preparation is an issue and contamination is common, therefore the substrate cannot be fully cleaned or ideally profiled as required for many repair materials. The desire to minimise downtime and deal with adverse application conditions creates a need for a fast curing, surface tolerant repair material.
New technology in polymeric materials has led to the development of the first fast curing epoxy-based, surface tolerant emergency repair metal, called Belzona 1212. This material opens new opportunities when ideal surface preparation of the metallic substrate cannot be achieved due to lack of time or resources and can reinstate equipment for years of service. With a high level of tolerance to surface contamination and excellent adhesion to manually prepared substrates, Belzona 1212 is set to become a preferred choice for emergency repair applications. After mixing of the two components, this material will cure rapidly as low as at 5°C (41°F).
Surface tolerance
Belzona 1212 provides excellent adhesion to surfaces contaminated with an extensive range of oils and fuels. It can also be applied to damp and wet surfaces as well as underwater. When applied to contaminated ground mild steel surfaces prepared in accordance with SSPC-SP11/ISO 8501-01 St3, the material demonstrates excellent adhesion. Fig.1. shows the dolly pull off adhesion of the system when applied to oil contaminated, wet and underwater surfaces, tested in accordance with ASTM D4541.
Adhesive performance is maintained on ground steel when the surface is contaminated. Fig.2. shows the tensile shear adhesion of the system when applied to both grit blasted steel, shown in blue, and ground steel as shown, in orange, when tested in accordance with ASTM D1002. The adhesive strength of the system to ground and grit blasted steel is similar regardless of levels of immersion, contamination and surface preparation.
Cure and return to service
To minimise downtime, it is important that a repair material cures and develops mechanical strength quickly. This system will cure rapidly after mixing of the two components, even in low temperatures without compromising on durability or strength. At low ambient temperatures, this repair system will still exhibit the same robust, hard-wearing properties synonymous with Belzona epoxy technology. Fig.3. shows the development of adhesive strength with time at variable temperatures.
To demonstrate the speed of cure and strength of the system, following a 90 minute cure at 20°C (68°F), a 1in square bracket bonded with Belzona 1212 will be able to support a tensile load of greater than 200kg (440lbs). After a four hour cure at 20°C (68°F), the same bracket will be able to support a load of greater than 1000kg (2204lbs). The material will continue to develop mechanical strength and once fully cured, the bracket will be able to support a load in excess of 1,800kg (3,968lbs).
To cope with harsh operating conditions, the material must be strong, durable and robust, where one of the most important characteristics is compressive strength, i.e. the ability of the material to resist failure when stressed axially under compressive load. When tested in accordance with ASTM D695, the compressive strength of the ambient cured system is typically 12375 psi (85.3 MPa), highlighting its high mechanical performance.
Product suppliers, applicators, end-users and owners alike have long faced the challenge of reducing the level of surface preparation without degrading performance of the repair material. To overcome this apparent disparity between levels of cleanliness and product performance, many new products are being developed.
New technology in polymeric materials has led to the development of a fast cure epoxy-based product, which opens new opportunities when ideal surface preparation of the metallic substrate cannot be achieved due to lack of time or resources. Where conventional repair composites would be ineffective and perform poorly, Belzona 1212 bonds tenaciously onto steel substrates even when surface preparation is minimal or if the substrate is heavily contaminated with oil or water. Belzona 1212 provides a cost-effective repair that can reinstate equipment for years of service.
Levente Bazsanyi is product manager at Belzona Polymerics.
