Design of an anticorrosive weldable primer for steel protection

This development is staged into work packages to enable the primer formulation to be developed (composition, deposition methods, curing conditions), tested and validated. The project will develop a demonstrator with the best candidate primer for dissemination activities.

Current primers mainly use zinc particles

Recently there has been an increase in the use of primed steel being used in steelwork construction projects. The primer protects the steel from corrosion, but those primers generally need to be removed before welding; removal is usually performed by abrasive blasting or locally by use of an angle grinder or equivalent, which adds to the fabrication costs. That is why there is a need for the primer to be weldable and although there are already new primer products on the market which claim to provide good corrosion protection and to be weldable, these products often need to be applied in thin layers to be weldable (about 25 microns thick coating to enable an arc to strike through and reduce the chances of porosity due to their zinc content). This reduces their anti-corrosion performances; that is why they are not often used. The recommended primer thickness for adequate protection (50-75 microns) necessitates removal of the primer before welding because otherwise it can affect weld quality. Moreover the current primers mainly use zinc particles to provide a galvanic effect to prevent corrosion of the steel substrate and during welding of such coatings the zinc may lead to hazardous fumes and defects in the weld.

The project in greater detail

To provide good corrosion protection it is important that both good adhesion is achieved between the primer and the steel substrate and that the primer has good barrier properties. The "WeldaPrime" primer is looking to achieve both of these and by using nanotechnology to give good barrier properties without the need of galvanic protection by the use of zinc. Since most corrosion of coated steel structures occurs at voids or cracks within the coating, improving adhesion is also key to the success of the "WeldaPrime" project.

Hugh Williams (BCF) and Aurélie Rexach (TWI Ltd) have answered questions to explain the project in greater detail.

Who is involved in the "WeldaPrime" project?

The "WeldaPrime" project counts ten partners and is run by a group of four associations, who agree upon the scope of the work that the Research and Technical Organisations (RTOs) are to carry out in the "WeldaPrime" project:

• the European Welding Federation (EWF - Portugal; also Co-ordinating the project),
• the Croatian Chamber of Economy (CCE - Croatia),
• the Federacion Vizcaina de Empresas del Metal (FVEM - Spain)
• the British Coatings Federation (BCF - UK).

The research and development activity is undertaken by three RTOs:

• Lurederra (Spain) specialising in pyrogenic nanoparticle production and formulation of nanoparticle dispersions for further use in material formulation,
• TWI Ltd (UK) contributing in this project with their expertise in the fields of design of nanostructures applied to coating formulation on one hand and on the other hand, welding techniques and weld assessment,
• INM (Germany) focussing on coating formulation as well as testing and characterisation.

Three SMEs also take part in the project as elements of the supply chain or end-users and provide their own expertise on commercial viability and market assessment for the new primer:

• Loufakis Chemicals (Greece), a manufacturer and distributor of high quality chemical products,
• Thomas Swan & Co (UK), a manufacturer of speciality chemicals including a broad range of additives, coatings, resins and advanced materials,
• Talleres de Soldadura y Mecanizado (Spain), a machining company undertaking activities ranging from surface preparation to parts’ assembly via welding.

When did "WeldaPrime" start and how much does it cost?

The project (FP7 Project 605371) is a three-year project that started in February 2014 and will run until the end of January 2017. The EC funding for the project is EUR 2.1 million with consortium partners committed to add at least €600,000, giving a total project funding of over EUR 2.7 million.

What is different between the "WeldaPrime" product and what is currently available?

Industry is not fully satisfied by the current commercially available products that are based on a galvanic mode of action (generally using zinc). However during welding the metallic particles contained in the primer emit hazardous fumes and may cause metal fume fever. So the project is looking at both reformulating the resin matrix used in the coating to have low organic content and using an improved barrier protection mechanism rather than galvanic protection, where the incorporated nanoparticles provide enhanced barrier against moisture and oxygen and thereby provide protection against corrosion. The selection of the particles was undertaken around three main parameters:

• The particles should not result in hazardous welding fume emissions,
• The particles should not negatively impact the weld quality,
• The particles should enhance the anti-corrosion properties (either by enhancing the barrier properties of the coating or by providing a corrosion inhibition effect).

By keeping a highly inorganic content primer formulation it is expected to maintain good welding results since little combustion and degradation products and gases will be trapped in the weld pool.

How were the new criteria set?

The "WeldaPrime" project had at the time it applied for EC funding agreed upon the approach of using nanoparticles as a feasible route to develop a zinc-free primer. The EC approved FP7 funding for this novel approach to solve the problem of both reducing health risks and also saving time and money.

The project then at its outset carried out a survey of the industry to assess the criteria that users were looking for in a weldable primer. Based on the responses received, the project was able to agree on the key steps it needed to undertake during the project to develop a new primer that would satisfy the industry needs.

A major part of the initial work in the project was to evaluate a number of current products on the market to both discover their actual properties as well as their shortcomings. This involved conducting primer application trials and evaluating the mechanical properties – abrasion, impact and adhesion strength – and their corrosion resistance. The primers were then evaluated for their welding and thermal cutting performance; the welding and cutting trials included evaluation and analysis of the fume produced in these operations and the speed at which these could be carried out. These tests set a series of minimum requirements that any new primer would have to meet in order to compete in the marketplace.

The project is seeking to develop a primer that can be used as widely as possible without users having to develop new application practices and therefore it will be applicable by airless and normal spray techniques as well as being brushable or able to be applied by roller.

What sector is targeted by the "WeldaPrime" primer?

The project focussed on application to carbon steel in a wide range of industries such as the oil and gas, construction, heavy duty steel and marine industries. These industries are the principal users of weldable primers in Europe; and this project is looking to reach this large sector of users as the project output will be easier to commercially sell at a competitive price if the number of potential users is high.

At what stage is the project currently at?

Following the research experiments, two hybrid highly-inorganic primer formulations have been selected as candidate formulations to go through testing and welding assessment (currently on-going activities). Both formulations are based on a hybrid organic-inorganic resin matrix; the inorganic part of the matrix provides the barrier property, while the organic part provides enhanced mechanical properties and flexibility and durability of the coating. The barrier property of the matrix is reinforced by the incorporation of inorganic nanoparticles in the resin matrix to increase the density of the primer and reduce the pathways for humidity and hence improve the barrier properties of the system.

What are the next steps?

The research work has produced possible primer formulations that are still being refined and the successful trial products will undergo a full set of mechanical, corrosion and most importantly welding and cutting trials to ensure that they perform as required. Included in the trials are over-coating tests with existing topcoats to ensure that the primer is compatible with products currently used to coat steel in the different industries targeted by the WeldaPrime project.

The trials form a major part of the project, but in parallel of validation by the end-user partners will also start refining the commercial and health and safety (H&S) assessment of the product as well as demonstrating a proof of up-scalability from laboratory samples to the production of larger volumes. This approach aims at ensuring that the primer can be made economically on an industrial scale. The primer characteristics and specifications combined with the commercial, H&S assessment and the proof of scale-up by project partners are the three key points of the WeldaPrime work to demonstrate that the primer is a commercially viable product that could save industry time and money as well as being safer to use.

The best candidate primer will be used to prepare demonstrators for dissemination activities.

How to know more about this primer?

The "WeldaPrime" Consortium is planning to hold a major workshop in late 2016 and attend conferences at which the performance and specifications of the primer will be presented to paint manufacturers, steel producers, fabricators and regulators to ensure that as large as possible audience is aware of the novel primer developed by the WeldaPrime project.