Anti-Corrosion Industry

Ductile Cast Iron pipes being Arc Sprayed automatically with Zinc

Metal Spray for Anti-Corrosion is Not Limited to Zinc

A common oversight regarding anti-corrosive coatings is the belief that they can only be completed with Zinc, when in fact Metal Spray can offer 4 variations of anti-corrosion coatings all of which have their own identities:

Zinc 99.99%

• High corrosion resistance in alkali medium at pH7 to pH 12.
• Excellent protection against atmospheric corrosion.
• Life cycle time proportional to coating thickness- metal sprayed Zinc can be applied to whatever thickness you want as it isn’t a dipping process like galvanising.
• Inadequate in the case of higher salt content in air, as in coastal regions.
• Corrosion behaviour like that of hot dip galvanising.

Zinc Aluminium 85/15 alloy

• High Corrosion resistance also in low acid medium.
• Higher corrosion resistance against atmospheric corrosion than Zinc and aluminium.
• Higher corrosion resistance against chlorides and especially SO2 containing atmospheres than zinc.

Aluminium 99.5%

• High corrosion resistance in media from pH 4 to pH9.
• Suitable for SO2 containing industrial atmospheres.
• Protects well in marine atmosphere and in seawater.
• High heat resistance.
• Highly resistant against acidic contamination.

Aluminium Magnesium 5%

• Well suited to marine atmosphere and in sea or brackish water.
• The loss rate in these corrosive media is significantly lower than for pure Aluminium.
• AlMg5 metal sprayed coatings have a higher hardness than Aluminium and is easier to machine and can be polished. 

The Arc Spray process actually adds an extra variation to those listed above. With Arc Spray, we can mix the wires in both diameter (ability to vary the % composition of each alloy) and alloy.

 Bridges

One main area that utilise the Metal Spray process is utilised is with regards to anti-corrosive protection of bridges. The building of bridges requires a significant investment. Due to the environments in which the bridges are located, they are often susceptible to extreme conditions that result in rust and corrosion. For this reason, a high performance, proven corrosion protection coating is often required and specified. Bridges and bridge steelwork is also very large and hence metal spraying is an ideal solution as the work can be completed on-site without the need to dismantle the structure.

New Zealand has many bridge applications including the Auckland Harbour Bridge (NZ) (1958) and the Te Rewa Rewa Footbridge (NZ). Other bridges that have been coated include The Forth Road Bridge (UK) (1964), the Pierre-Laporte Suspension Bridge across the St Lawrence near Quebec, Canada (where from 1977-79 some 165,000m² was coated after failure of the original paint system over a six year period), Humber Bridge (UK), the Bosphorus Bridge (Turkey), Tsing Ma Bridge (Hong Kong) and the Clifton Suspension Bridge (UK).

For more Metal Spraying applications on Bridges, Click Here.

Rail Protection

Railway Tracks can be Metal Sprayed for Anti-Corrosion Protection.

Corrosive environments can reduce rail life vastly. Instances have shown that unprotected rails reported lifetimes of less than six months. In general, loss of rail sections can occur due to corrosion, as well as in more localised areas (e.g. around rail fastenings). It is also important to note that foot fatigue failures often occur as a result of foot corrosion. Corrosion pits (often unseen) on the bottom of the rail can initiate fatigue cracks which can then grow undetected, resulting in rail failure ¹.  

British Steel, the UK-based manufacturer of premium steel products, has launched a revolutionary new rail product, which can withstand the harsh and demanding conditions of being laid in some of the most corrosive of environments ².

¹ Extracted from: https://britishsteel.co.uk/what-we-do/rail/zinoco/

² Extracted from: https://www.industryupdate.com.au/article/british-steel-launches-revolutionary-new-rail-product

For more Metal Spraying on Railway and other Transport related applications, Click Here.

Wind Turbines - Metal Spray Protection

Descon Quimica of Spain has supplied a metal spraying system for wind turbine components to Granallados Molinero S.L. Molinero approached Descon because of its expertise in supplying automated metal spraying equipment and their industry specific expertise in relation to wind turbines. Molinero was new to the industry of thermal spraying wind turbine components and wanted to utilise the benefits of automating the process. This is in contrast to a lot of wind turbine thermal spraying which is carried out manually.

The issue surrounding atmospheric corrosion of wind turbines is significant, particularly considering that many turbines are situated in coastal/saltwater environments. It is for this reason that many manufacturers of wind turbines specify thermal sprayed zinc or zinc/aluminium alloys as a method of corrosion protection, to all or part of the steel wind turbine structure. The joint areas of the columns and the components being assembled are thermal sprayed to offer corrosion resistance in areas where paints may be damaged during assembly of these large items. Thermal sprayed coatings offer a very resilient finish, which is less susceptible to damage than many paint coatings.

For many years, Descon Quimica has been supplying metal spraying equipment and materials for the protection of wind turbine parts throughout Spain, as well as other anti-corrosion and engineering applications. Descon provides anti-corrosion protection for diverse industries including, liquid gas bottles, tube manufacturers, beer tanks, silos, parts of railroad bridges and aqueducts.

The spray equipment is being used by Molinero to spray components within the assembly that support the turbine blades. The actual coating with pure zinc is only one part of the process. To ensure optimum adhesion of the coating, the surface of the turbine part is first grit blasted to a profile of around 75 microns and a cleanliness of SA3. A robot mounted arc spray system then applies an even 120 microns of Zinc at a spray rate of up to 36 kg/hr. A final coating of epoxy paint is then applied. This is an excellent way to protect wind turbines from corrosion and offers up to 20 years protection.

The adaptability, flexibility and ease of use of the Metallisation Arc Spray equipment, has made the transition into metal spraying much easier for Molinero. One of the main reasons for selecting the Metallisation ARC140 (superseded model) is that it is easily integrated with the robot cell, which then controls the spray gun to start and stop the spraying. The 20m push / pull supplies package also allows the energiser, wire and wire dispensing system to be located outside the dusty spray booth, giving the system greater reliability.

There are many advantages of automating the spraying process. Obviously, these generally apply when there are batches of identical parts to process, as is the case at Molinero. Automatic spraying will enable a very uniform coating thickness. Not only is this beneficial to the coating quality but also as a commercial value. Typically, if components are manually sprayed and the specification calls for a minimum coating thickness of 120 microns, it is very difficult to maintain a consistent coating depth. Even an experienced operator would usually coat to a minimum of 120 microns and in places, up to 180-200 microns or more. Through automation, an even 120-micron coating is achievable, offering on average, material savings in the region of 40%. The spraying environment is also noisy and dusty. Through automation, the operator can remain outside the spray booth area.

Major advantages of the Arc Spray process are:

• That the coatings are available for almost immediate use, with no drying or curing times.
• There is no risk of damaging the component.
• The deposits possess a higher degree of bond strength than most other thermally sprayed deposits.
• The use of only compressed air and electricity mean more economic coatings.

For more Metal Spraying on Turbine applications, Click Here.

Internal Steelwork with High Humidity

Reason for use: Protection of condensation corrosion in area such as swimming pools, breweries, wineries, pasteurising plants etc.

Nuclear

Nuclear power plants also benefit from thermal spray coatings. Mainly utilised for corrosion and erosion minimisation and dimensional restoration of worn parts similar to power plants along with more specialist coatings such as radiation shielding coatings to protect workers or other components.

The nuclear industry extensively use materials such as Austenitic stainless steels because of their good anti-rust performance in corrosive environments. Inconel 625 is also suitable for these anti-corrosion coatings mainly used in chlorine-containing environments. In addition to their excellent ductility, formability, toughness, and weldability properties, these steels are being used everywhere in the world for their inherent mechanical properties.

Automated Metal Spraying at Laguna Verde Nuclear Power Plant Veracruz, Mexico

Reason for use: Protection of nuclear dry steam tubes against high temperature corrosion and erosion.

Metallisation customer, Lainsa, based in Mexico and part of Grupo Dominguis, provides metal spraying for corrosion protection of pipes used to exchange and transport dry water vapour in thermoelectric, conventional and nuclear power plants.

Metal Spraying for Corrosion Protection of Pipes

The application of metal spraying is critical, as the circulation of dry steam at high temperatures can lead to corrosion of the carbon steel. As a consequence of this corrosion the pipes can become perforated, which can lead to an unplanned closure of the plant resulting in a costly and inconvenient loss of electricity generation. To protect against corrosion the inner walls of the pipes are protected with a coating made up of several layers of cast metal alloys. The coating is extremely hard and resistant to abrasion, protecting against corrosion and improving the tribological properties, the resistance to wear and tear by friction of the water molecules contained in the steam.

Grupo Dominguis has developed the TIRANT 3® system, a worldwide innovative automatic system used to apply metal spraying to the inner surfaces of steam pipes. TIRANT 3® system is operated from outside the pipe, which means the only human intervention is the operation of the robot positioning and to change the metal wire. As a robotic, automated system that is pre-programmed, the metal spraying process is significantly extended without the need for rest periods and the only ‘down time’ is for robot maintenance.

TIRANT 3® System

The TIRANT 3® system also provides increased coating uniformity, therefore its resistance to corrosion, by keeping the selected parameters constant and consistent. In 2010, Lainsa successfully metal sprayed the inner surfaces of Cross Under pipes at Units l and ll of the Laguna Verde Nuclear Power Plant.

Using the TIRANT 3® system and the Metallisation Arc spray 140/S350 system, 300m² of steam pipes were metal sprayed in thirty four days. The project was commissioned by Comisión Federal de Electricidad de México, and had to be completed during a routine break in the refuelling of the units. The inner surface of the steam pipes was blasted to a cleanliness SA 3 before being metal sprayed to a thickness of approximately 500 µm. The coating was applied in three layers: An anchoring layer of nickel / aluminium alloy; an intermediate layer of chrome / nickel alloy and a surface layer of chrome / nickel alloy.

The manual application of metal spraying requires a great deal of physical effort with frequent rest periods, which is mainly due to working in confined spaces, thermal stress and the need for independent and semi-independent breathing equipment and face masks.

The manual operator uses the gun to project the molten metal particles onto the surface, which can entail bending and kneeling in difficult and uncomfortable positions, while spraying pipes varying in size from 1 metre in diameter and up to 25 metres long. Due to the inaccessibility of pipes with smaller diameters, they are usually left untreated and prone to corrosion. The flexible TIRANT 3® system is the perfect solution for metal spraying small diameter pipes.

The metal spraying process also produces a large amount of fume, sparks and particles of metal dust, which means manual operators must have appropriate protection, including fireproof clothing, masks and a supply of breathing air. In certain industries additional protection must also be put in place, such as protection against ionising radiation, if the work has to be carried out in a radiological area.

Another inherent problem in manual application is the task of achieving uniformity of the coating thickness, so a reduction in thickness variations will result in greater resistance and greater surface protection. The difficulties arise due to the position of the operator inside the pipe. Movement is restricted and the visual distance or perspective of the coating application can be hampered making it more difficult to obtain a uniform layer. While working on metal spraying the inner surfaces of the Cross Under pipes of a Boiling Water Reactor at the Nuclear Power Plant, these conditions were exacerbated with the additional risk of exposure to radiation for a manual operator. Opting for an automated process to metal spray these pipes reduced the risk of radiation by 70%. This was achieved by adopting protection measures using three basic principles – distance shield and time.

The TIRANT 3® system has been developed in direct response to the need for a simple, remote tool that removes manual application of a coating, while guaranteeing a uniform coating layer. The thickness applied to the surface of the pipe depends on four factors: The wire type used; the forward speed; the rotation speed and the distance of the Arc spray 140 from the wall of the pipe. The TIRANT 3® system, used in conjunction with Arc spray 140/S350 equipment, is versatile and appropriate for different pipe diameters, projected materials and desired thicknesses. The control software enables consistent and uniform forward and rotation speeds in relation to the thickness of the wall of the pipe. The TIRANT 3® system also has an automatic folding and unfolding system making it suitable for metal spraying pipes in all shapes and sizes.

The Metallisation Arc spray 140 system is the ultimate solution to today’s demands for high performance Arc spray equipment. The patented ‘Synchrodrive’ push/pull system provides constant, reliable and trouble free operation, utilising two gearboxes linked by a flexible drive. The drive system guarantees that the ‘push’ and ‘pull’ elements cannot be out of synchronisation, which ensures consistent wire feed over a long range, of up to 20 metres, making spraying at a distance much easier. The benefits of the Arc 140 system include a choice of coating textures, low running costs, high throughput, portable wire dispensing, safety interlocks and steel reinforced conduits. In the Metallisation Arc spray process, the raw material, a pair of metal wires, is melted by an electric arc. The molten material is atomised by a cone of compressed air and propelled towards the work piece. This spray solidifies when it hits the surface of the work piece to form a dense coating, which protects against corrosion or repairs components. Sprayed coatings may also be used to provide wear resistance, electrical and thermal conductivity or for free standing shapes.

Corrosion Under Insulation

Using TSA to Protect Pipelines from Corrosion Under Insulation (CUI)

Reason for use: Cost effective corrosion protection against aggressive corrosion under insulation (CUI).

In the petrochemical industry Corrosion Under Insulation (CUI) in pipeline systems consumes a significant percentage of the maintenance budget. A large portion of this money is spent on expensive items such as external piping inspection, insulation removal and re-installation, painting and pipe replacements. CUI prevention strategies provide long term and reliable prevention of CUI that move towards inspection-free and maintenance-free piping systems and significant maintenance cost reductions.

Coating with TSA (Thermal Sprayed Aluminium), using Metallisation flame spray equipment is one method that a number of operators within the petrochemical industry have adopted. TSA is found to be a cost effective solution compared to other systems when reviewed over the lifetime of the facility. One of Metallisation’s customers has an ongoing programme for applying TSA at a petrochemical plant, as a solution for the long term protection against atmospheric corrosion and CUI.

One specific project is a three quarter mile long marine jetty pipeline that is used for the transportation of lube oil and is exposed to the harsh marine environment. Other projects on this site have included a full range of pipes and vessels, including work on live operating plant.

To ensure the success of the thermal spraying process, the preparation of the pipeline surfaces is critical. For this project the pipeline surface was prepared by grit blasting with garnet to give a sharp angular profile for the TSA to bond to. As part of the QA/QC process, the blast profile was regularly checked using Testex tape to ensure it meets the required 75-125 micron specification.

The grit blasted surface was then given a visual inspection, using 10x magnification, to check the surface cleanliness and finish. The pipes are also given a ‘tape test’, which checks for dust contamination of the blasted surface. The tape sample is then visually inspected against white and black backgrounds for signs of dust particles. The final quality test is a salt contamination test.

Using a small flexible container a minimal amount of testing solution is applied and agitated on the surface of the blasted pipe. This solution is then checked for the presence of salt using a test kit pipette. Once all of these tests have been passed the pipelines are ready to be thermal sprayed with aluminium.

A huge advantage of the Metallisation equipment and process is the flexibility and long supplies, which provide a safe working environment and ease of use for the operators. In this project the gas bottles and compressor were situated in a remote supply area, which gave easy access to the gas cylinders and enabled manifolding for fewer cylinder changes. In elevated applications such as vessels and towers, the cylinders can remain on the floor while the spray system is elevated tens of metres.

This situation therefore requires less complex scaffolding as the heavy bottles are not scaffold mounted. The 30 metre supply package, consisting of gas, oxygen and air, was fed from the overhead supply area down to the control panel. The pistol is then a further 10m away from the control panel. This setup allows around a 60m length of piping to be sprayed without having to move the cylinders and air compressor, giving significant productivity benefits in a very difficult environment.

The contractor on this specific job site is using two Metallisation Flame Spray systems in different spray locations. Once the blasting and inspection is completed, the TSA application starts. Typically, blasting and inspection is completed in the morning taking approximately four hours.

The TSA is applied in the early afternoon for around three hours and the final sealant application at the end of the day. The TSA is applied with a methodical work pattern with the pipe topside coated first, then the underside. The long supplies package allows the sprayer and wireman to move freely around the worksite in the most efficient manner to suit the specific area.

The MK73 deflected extension is perfect for those difficult to access areas commonly found at petrochemical sites and has been designed specifically for this application area. It comes in three lengths – 150mm, 300mm and 450mm. The extension unit can spray directly forward or at a deflected angle up to 90^o by varying the deflector air pressure. The deflection nozzle can also be rotated through 180^o to allow spraying in a 360^o arc around the pistol. The long supplies system provides flexible working conditions, particularly useful when spraying the underside of the pipes.

Following the application of the TSA, the pipelines in this specific application were sealed with Intertherm 50 sealer, which was applied until full penetration was achieved. In some CUI related environments, no sealer is applied, especially where the spray area is operational and hot.

During the application of the TSA the operators periodically checked the coating thickness using a DFT gauge and made appropriate corrections along the way. The specification for this particular job was 250-500 microns. The QA/QC Inspector for the project also checked and recorded the coating thickness throughout the process. To support the QA/QC process the spray operators produced witness plates on a daily basis, which were then tested for adhesion to ensure it met the minimum 1000 psi – 6.9MPa coating thickness. Audit bond strength testing was also carried out periodically on the actual sprayed pipe sections.

Thermal spraying involves the projection of small molten metal particles onto a blast prepared surface. Upon contact, the particles flatten onto the surface, freeze and mechanically bond, firstly onto the blasted substrate and then onto each other, as the coating thickness is increased. To create the molten particles, a heat source, a spray material and an atomisation/projection method are required, in this instance the customer opted for the flame spray process.

Cathodic Protection of Steel in Concrete

For many years industrial companies have fought to protect steel reinforced concrete from corrosion. The prime causes of corrosion in concrete include salt, chloride and de-icing treatments. The salt seeps into the concrete and erodes the steel reinforcing bar (rebar) causing cracks and spalling in the concrete and eventually the potential for failure of the structure. One very effective, long-term solution is metal/thermal spraying the concrete with zinc or a variety of zinc alloys. This is a technology that protects or extends the life of a wide variety of products in the most hostile environments.

The images below show the rebar corrosion in concrete.

Re-bar Corrosion in Concrete

The majority of metallised zinc cathodic protection systems are operated in galvanic or sacrificial mode. However, metallised zinc cathodic protection systems can be, and are in many instances, operated in impressed current mode. The sprayed coating, a high purity zinc alloy, is connected to one pole of a DC power supply. The steel rebars are connected to the other pole of the power supply. The electrical circuit is completed between the rebar and the zinc by the presence of moisture in the concrete. The action of the corrosion cell causes the zinc to corrode in preference to the steel rebars, therefore protecting the rebars from corrosion.

Cathodic Protection with Zinc Coating

The process of spraying the zinc onto the substrate ensures that there is a good, even connection path between the coating and the rebars through the concrete. Prior to metal spraying damaged sections of concrete need to be repaired with rebars also repaired or replaced. The surface needs to be lightly blasted to remove any surface dirt and provide a good key to enable the coating to bond. The coating would then be applied with either a Metallisation Arc140, Arc701 or Arc170 system, depending on the size and accessibility of the structure. Typical bond strength is in the region of 3MPa for zinc and coating thickness would be between 300 and 500 microns. The above picture shows an Al-Zn-In metal spray coating being applied using the Metallisation Arc spray system.

Cathodic Protection of Steel in Concrete Bridges

The cost to apply metal sprayed coatings to large concrete structures is not insignificant, particularly when many structures are difficult to access, such as bridges.

However, the long-term benefits can make the process extremely commercially attractive. If performed correctly and depending on the coating applied, the process can offer corrosion protection for up to 20 years before the next significant maintenance is required. The protection offered can greatly prolong the life of the structure and also prevent costly accidents from cracked sections falling from the structure. Once applied, the coating requires minimal maintenance. If required for aesthetic purposes, Metal Sprayed coatings can also be painted or powder coated.

Al-Zn-In Application of San Luis Pass Bridge, USA

A recently developed alloy of aluminium, zinc and indium has been used in a small number of applications. This material is more active than zinc and it is claimed to not require an impressed current to provide adequate levels of corrosion protection. A significant application of the Al-Zn-In alloy in the US is the San Luis Pass Bridge near Galveston, Texas. More than 30,000m² of concrete beams and caps are protected with this alloy, installed using Metallisation ARC 700 units by Corrosion Restoration Technologies of Jupiter, Florida.

Oregon Department of Transportation (ODOT) demonstrates another success story for cathodic protection on concrete. In a bid to reduce the high costs of bridge reconstruction, ODOT has applied a system of metallised zinc anodes and impressed current cathodic protection. This process has been used to protect its Cape Creek Bridge from corrosion and subsequent reconstruction. The bridge is exposed to a coastal environment and is subject to attack by chloride from the salty air. Prior to the cathodic protection project on the bridge, it had suffered substantial concrete spalling on its columns and under deck. By selecting to protect the bridge in this way ODOT saved over $13 million by not having to reconstruct the bridge. The cost of cathodic protection is quite expensive. This is due to the requirement of a movable work platform, which is enclosed to contain the abrasive blasting and zinc spraying residues. These measures are critical when spraying zinc to protect the environment. However, when compared to the cost of reconstructing a bridge the size of Cape Creek Bridge – the savings are phenomenal.

Dave Wixson, Metallisation distributor in the US says: “Cathodic protection is a cost effective way to stop rebar corrosion in existing structurally sound structures. Re-bars in dry alkaline concrete are protected by a passive ferric oxide film, however, when the rebar is hit with 250 ppm chloride solution, generally from salt, the protection breaks down. The protective ferric oxide film is converted to red rust and corrosion begins.

Concrete thickness >4cm (>1.5 in), will prevent chloride penetration. For exposed rebar and thin concrete, where there is chloride concentration in excess of about 250 ppm, rebar corrosion will be initiated with the red rust spalling adjacent concrete. Protecting the re-bar with a barrier using an impressed or passive cathodic protection system, counters the corrosion.”

Cape Creek Bridge, Oregon (USA)

Oregon Department of Transportation (ODOT) demonstrates another success story for cathodic protection on concrete. In a bid to reduce the high costs of bridge reconstruction, ODOT has applied a system of metallised zinc anodes and impressed current cathodic protection. This process has been used to protect its Cape Creek Bridge from corrosion and subsequent reconstruction. The bridge is exposed to a coastal environment and is subject to attack by chloride from the salty air.

Prior to the cathodic protection project on the bridge, it had suffered substantial concrete spalling on its columns and under deck. By selecting to protect the bridge in this way ODOT saved over $13 million by not having to reconstruct the bridge. The cost of cathodic protection is quite expensive. This is due to the requirement of a movable work platform, which is enclosed to contain the abrasive blasting and zinc spraying residues. These measures are critical when spraying zinc to protect the environment. However, when compared to the cost of reconstructing a bridge the size of Cape Creek Bridge – the savings are phenomenal.

Dave Wixson, Metallisation distributor in the US says: “Cathodic protection is a cost effective way to stop rebar corrosion in existing structurally sound structures. Rebars in dry alkaline concrete are protected by a passive ferric oxide film, however, when the rebar is hit with 250 ppm chloride solution, generally from salt, the protection breaks down. The protective ferric oxide film is converted to red rust and corrosion begins.

Concrete thickness >4cm (>1.5 in), will prevent chloride penetration. For exposed rebar and thin concrete, where there is chloride concentration in excess of about 250 ppm, rebar corrosion will be initiated with the red rust spalling adjacent concrete. Protecting the rebar with a barrier using an impressed or passive cathodic protection system, counters the corrosion.”

Many thanks to Palmer Consulting of France, TMS of the USA and Corrosion Restoration Technologies Inc (now part of Structural Group, Inc.) of the USA for information supplied.

Laser Cladding for Continuous Caster Rolls

Reason for Use: Increase wear resistance and provide an effective corrosion resistant barrier.

Laser cladding is a cost effective method of applying a relatively thin layer of an expensive, high performance alloy, which increases wear resistance and provides an effective corrosion resistant barrier.

Continuous caster rolls are used in the steel industry to cast continuous solid forms from liquid steel. The rolls are exposed to thermal fatigue, high temperatures, bending stresses, corrosion oxidation and abrasion.

The standard method of protecting caster rolls is by submerged arc welding with a 400 series stainless steel, which can suffer heat affected zone cracking between weld runs. Laser cladding the caster rolls is a cost effective method of applying a thin layer of a high performance alloy, in this case nickel based super alloys, to improve wear and corrosion resistance.

Laser cladding is a process that falls into the range of hard-facing solutions, which can be used to increase corrosion resistance, wear resistance or impact performance of metallic components, using a method of applying a fully dense, metallurgically bonded and virtually pure coating. Rolls that have been laser clad have been proven to last up to five times longer than the standard submerged arc welded rolls.

Materials - Main Deposit: Nickel based super-alloy

Method

Preparation

1. Old or worn rolls may need to be repaired prior to laser cladding using weld repair.
2. The rolls are pre machined to a size about 2mm smaller than the finished diameter.
3. The surface of the rolls must be clean and unoxidised and can be presented straight from the lathe.
4. If the rolls need to be cleaned prior to laser cladding, this can be done through degreasing or blasting.

Equipment: Metallisation MET-CLAD System

Application of Laser Cladding

The surface of the roll is laser clad with a nickel based super-alloy using a fine, accurately controlled laser beam, which results in an extremely strong wear and impact resistant coating.

The rolls are then stress relieved to reduce residual stress and finish machined to the required size. The laser cladding process utilises a precisely focused high power laser beam to create a tightly controlled weld pool into which a metallic powder is applied.

The powder is carried by a stream of inert shielding gas, which is blown coaxially through the laser beam. The highly controllable nature of the laser beam allows fully dense cladding with minimal dilution and a perfect metallurgical bond. The very low heat input, associated with a laser, minimises distortion and results in a refined microstructure. Due to the high level of accuracy and control, laser cladding enables the cost effective application of high performance alloys to tackle a wide range of engineering issues.

Typical deposition rates are between 60 and 100 g/min around 3-6 kilograms per hour, depending on the material being deposited and the geometry of the work piece. To apply a laser clad coating the cladding head has to be fed the appropriate with four key things; a laser beam, process gasses, the metallic powder and cooling water.

The Metallisation MET-CLAD laser cladding control console provides integration and control of the complex component parts. The MET-CLAD system is a simple to use control system with touch screen HMI and is based on the Metallisation HVOF and Plasma control concept.

The control console offers mass-flow control of the laser shielding and powder feed gas for repeatable cladding. The laser can also be housed and controlled within the cladding console up to 3kW or as a separate enclosure for larger laser sizes. The control interface for production operations is simple, but it can be drilled down to a great level of complexity for coating development. Repeatable operations are easily programmed or they can be linked to a barcode system for even simpler programming.

The process gases are mass flow controlled for repeatability of the coating process. Comparison of Coatings The image on the left, shows a laser clad surface after 118 ktonnes. The image in the middle, shows a sub arc welded surface after 63 ktonnes. In the right hand image, the top roll is sub arc welded and the lower roll is laser clad.

Comparison of Coating Processes

The above table gives a broad comparison of coating processes. The data shown is based on typical applications and parameters. There can be exceptions to this data, dependent on the specific applications and parameters, MSSA will be happy to offer advice for specific applications.

Conclusion

Laser cladding is a cost effective method of applying a relatively thin layer of an expensive, high performance alloy, which increases wear resistance and provides an effective corrosion resistant barrier. The minimal heat affected zone removes problems associated with weld decay. This means that laser clad continuous caster rolls can last up to five times longer than traditional submerged arc welded rolls.

Anti Corrosive Coating of Foot Bridge 

Flame Spray TSA used on an Offshore Platform

The Battle Against Rust - Metal Spray Applications

For more information on Metal Spray equipment or consumables, call us on (07) 3823 1004, or email using our contact form.

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