UV LED curing for OCTG pipe coating

In this article:

• • • • Liquid paint curing: characteristics and differences of the 3 main methods  
      • Water-based coating and UV LED curing compared: a realistic simulation to quantify consumption and benefits
      • A complete revamp to improve plant performance
      • A brand new UV LED coating plant for OCTG pipes

From water-based coating to UV LED curing of OCTG pipes: Movingfluid evolves with the market    

The industrial world always poses new challenges: what works today may no longer be suitable for production tomorrow, and market developments (commercial, regulatory or technical) lead to major changes within plants.

An example? Coating types and methods. Indeed, in recent years we have witnessed the introduction of innovative solutions alongside the more traditional ones: Thus, alongside the more classic water-based coatings, UV curing systems have been developed with mercury and, more recently, with LED.

A promising technology – in terms of efficiency and savings – that Movingfluid has already become acquainted with thanks to two OCTG (Oil Country Tubular Goods) pipe coating projects developed for a global steel production giant.  

Liquid paint curing: characteristics and differences of the 3 main methods

UV LED curing is the latest technological breakthrough in industry for the external coating of pipes for the oil&gas sector. An area that requires:

1. highly reliable and repeatable processes;
2. procedures compatible with high production volumes;
3. continuous operation over several shifts; stringent quality standards.

This is why many companies operating in this segment have preferred to abandon (or are preparing to abandon) traditional coating in favour of more high-performance alternatives. 

But let us see in detail what the difference is between these 3 methods: 

1. water based coating; 
2. UV coating with traditional lamps; 
3. UV LED curing. 

1. The water-based coating with hot-air ovens: a timeless classic

The industrial coating of OCTG pipes has mostly a protective and non-aesthetic function, which is especially useful for export parts.

Systems that adopt water-based solutions are rather easy to handle and therefore still very popular, but they have a lot of room for improvement:  

1. paints have a solid content typically of 40-55%: this means that only about half of the purchased product has coverage capacity (moreover, not all of the solid part is sprayed onto the pipe: most water-based paints generate overspray, i.e. some of the spray ends up in the environment and not on the pipe); 
2. the other half, i.e. the water component, must be completely evaporated for the paint to solidify; 
3. which requires the use of hot air or IR/air ovens   
4. drying times are rather long (from a few minutes to a few hours) and, consequently, the energy consumption is high  
5. the overspray generated in the paint booth is not recoverable and, on the other hand, creates waste products (sludge, contaminated liquids, etc.) which must be disposed of.  

2. UV coating with mercury lamps: a solution that risks remaining ‘on the sidelines’

Some of these critical issues have been overcome by conventional UV curing, which employs 100% solid paints, with no water part (the product yield is total and can even be recovered!), cured instantaneously via UV mercury lamps.

Unlike conventional drying, UV lamps trigger a photochemical reaction that hardens and fixes the coating to the pipes. However, there is one ‘however’, or rather three:  

1. the installed power for the system to function is rather high;  
2. the amount of waste heat is also significant and, therefore, requires treatment to make the work environment comfortable; 
3. during the process several harmful substances are released, such as ozone and mercury, which need to be managed.   

Added to this is a further legislative obstacle: According to the latest updates, from 2027 this type of lamp will be banned within the European Union. For this reason, despite possible derogations and postponements, some companies already prefer to go for the new development.   

3. UV LED curing: the top-of-the-line for coating

No longer mercury, but LED light: the lamps used in this system use a specific wavelength to cure the paints, which again are 100% solid and recoverable.

LED technology has numerous other advantages: 

1. it lasts much longer than mercury, thus reducing the cost of replacement or repair of the system;  
2. it has a low thermal load, thus imposing no excess heat management systems within the factory; 
3. it occupies much less space than the water-based paint solution: the firing booth occupies an area of approximately 3×2 m2 compared to 15×7 m2 of the air oven; 
4. it guarantees high electrical efficiency;  
5. it produces neither mercury nor ozone (but still needs fume treatment), so it has a much smaller environmental footprint (and disposal cost); 
6. the UV LED curing system can be switched on and off at any time and reaches the required temperature in seconds, without wasting energy and money.   

Water-based coating and UV LED curing compared: a realistic simulation to quantify consumption and benefits

We know that talking about savings in a generic way is not enough: those who invest in industry want precise numbers. To get a more concrete idea of the benefits generated by savings, we used actual production data from the steelworks and applied them to those of the two painting techniques. This is what came out.  

Production parameters considered

• Average pipe diameter: approx. 220 mm; 
• Average length: 10 m; 
• Dry paint thickness: 45 microns; 
• Production: 60-120 pipes/hour (average 90 pipes/hour) 
• Operability: 3 shifts, 24h/day, 330 days/year 
• Average surface area per pipe: approx. 6.9 m², 
• Estimated annual output: about 712,800 pipes approximately 4,920,000 m² coated/year.  

Paint consumption

Industrial space

• Air oven + handling: ≈ 200 m² 
• Complete UV LED tunnel: ≈ 60 m² 
• Average industrial cost considered: 120 €/m²/year 

Annual operating costs (OPEX)

*Assuming 24 h/day operation for 330 days/year at an average cost of 0.06 €/kWhₜₕ.

In summary, a UV LED system (as opposed to one using water-based coatings) guarantees: 

• operational savings of approximately 844,000 euros per year; 
• payback time for the purchase of 16 months.  

Unrivalled operability and economy

In the high-productivity OCTG context such as that of the company examined here, the real cost is not the price of the paint, but that per cured useful m². Industrial space, on the other hand, is immobilised capital.

If we follow this reasoning and take up the simulation results, it becomes clear that UV LED technology transforms the coating process from a cost centre to a margin lever. When the final quality of the coating is equal, the comparison between the two methods is overwhelming. A few key points are enough to summarise it:  

1. the air oven dries mainly water; 
2. the UV LED system drastically reduces operating expenses; 
3. the investment costs for UV LED are higher, but the payback is rather quick; 
4. the environmental impact it is significantly lower in UV technology; 
5. productive flexibility and speed are unmatched. 

In production-intensive industrial environments, the UV LED option is not just an incremental technological development, but a structural change in the economic model of the coating process. 

A complete revamp to improve plant performance

For this reason, too, some companies have already turned to UV over the past decade, abandoning water-based coating altogether or in part.

This included the multinational company that, on a couple of occasions, requested the support of Movingfluid: in the first instance, to completely renovate the existing mercury UV curing plant in use; and then a second time to develop an entirely new solution with UV LED technology.  

An unreliable system that caused downtime and massive waste

At its plant in Saudi Arabia, the customer used a machine for coating pipes with mercury lamps: a choice that turned out to be rather unfortunate, not so much because of the system itself, but because of the inefficiency of the system, which was built by another supplier.

The main problems included: 

1. extended downtime 
2. low paint utilisation 
3. poor process and quality control.  

The areas most in need of improvement were spraying, lamp cooling and paint recovery. Critical issues attributed to a faulty design, which also resulted in frequent clogging of the recirculation system and several manual setup points, such as adjusting atomisation and fan pressure, and nozzle position.

The result: unstable production and long cycle change times, with a much lower than expected paint utilisation rate (only 61.81%). 

Intervening upstream to solve downstream problems

Thanks to our experience in the field of industrial coating, we were able to propose a series of improvements that went to the root of the issues reported by the company.

First, we focused on everything that caused downtime and dispersion, starting with the guns. A challenge within the challenge was the variety of part sizes, which can range from 5-6 m up to 15 m in length, and from 100 mm up to 350-400 mm in diameter, depending on production requirements. The solution proposed by Movingfluid eliminates the need for manual control of the guns, which automatically adjust themselves based on the pipe measurements.

The flow of paint can also be controlled by an autonomous system by means of an electric pump that adapts the flow of product to the diameter of the pipe. As a result, filters will no longer clog because the paint quantities will always be calibrated to the actual size of each part. for Correctly handling the spraying – a phase often overlooked both during design and in the investigation of problems – all subsequent issues are therefore solved in a chain.

A distinctive approach of our Problem solvers who, in addition to being able to act on existing machines for their optimisation or conversion, know how to develop plants from scratch, even with the latest UV LED curing system. 

A brand new UV LED coating plant for OCTG pipes

This is highlighted by the second project developed for the steel company, which has decided to introduce the UV LED method at its Saudi Arabian site. The solution proposed by Movingfluid makes it possible to manage the wide range of pipes handled without difficulty, including the shortest ones. These, passing in line from the coating station to the drying stations, are in fact in danger of tipping forward, but inserting a central support would cause a gap in the coating. Thanks to a system (already popular in other similar plants) of blocking and counterweighting at the inlet, even short pipes can be painted flawlessly.

After painting, the parts continuously pass through a double curing area, which is connected to both the fume extraction apparatus and the overspray recovery area. The latter, in particular, is one of the winning aspects of UV coatings: Inside the spray booth, two automated cones scrape the unused product from the surface and convey it to the designated area, where it is purified for reuse. An almost total recovery resulting in for real savings.  

Change can be extremely positive if you know how to manage it and which solutions to choose to improve productivity. Have no doubt: Movingfluid is the ideal partner for growth!

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