Protecting steel structures in a demanding environment

By Simon Daly 

Corrosion is a destructive force that will cause significant disruption to any steel structure left unprotected and so the need to protect assets when the stakes are high is vitally important. Perhaps none more so than in the potentially dangerous environments that exist in the oil and gas sector. In 2000, the Khazzan natural gas field was discovered in the Omani Governorate of Ad Dhahirah and is now the largest new upstream project in the Sultanate. Located around 350 km south-west of Muscat, construction began on the site in 2014 and this year will see production begin to deliver an expected one billion cubic feet of gas each day. The project is operated by BP Oman and jointly owned by that organisation and the Oman Oil Company Exploration and Production (OOCEP). More than $16 billion has been invested in the project, which will involve a15-year drilling programme and 300 wells in total. 

BP has given the design, build and operating responsibility to sector specialist, Petrofac who, in turn, have subcontracted much of the engineering and fabrication work to Elco. A wholly owned subsidiary of the Zubair Corporation, Elco is one of the world’s leading heavy engineering and fabrication companies located in Oman. Since its foundation in 1976, Elco has established a solid reputation for offering complex manufacturing solutions including design, engineering, fabrication, supply and construction services to the oil and gas sectors.

Selecting the optimum solution

Part of Elco’s work is to construct the onshore processing facility for the gas field. To ensure it is adequately protected in what has proven to be an extremely corrosive environment, Elco has selected Hempel to provide the anti-corrosive coatings for the structural steel pipe racks. The system that Elco has chosen includes Hempadur Avantguard 750 as a primer combined with Hempadur MIO 47950 and Hempadur HS 55610.

In this environment, it is important that the primer delivers the best anti-corrosion protection available and retains its performance for extended periods and in extremes of temperature. In this case, these rigorous demands are being met by Hempel’s Avantguard technology.

Silicates or epoxies?
Before Avantguard was introduced to the market, fabricators would be faced with the choice of opting for a zinc silicate or a zinc epoxy coating. Zinc silicates, whilst offering enhanced anti-corrosive properties, are generally low in mechanical strength and require specific conditions for application. Historically, however, Zinc epoxies have been considered inferior in terms of corrosion protection but with the advent of our Avantguard technology, we are changing that perception.

In both types of coating, the zinc is the sacrificial element and corrodes instead of the iron to leave the underlying steel intact. But this process, known as the galvanic effect, is only effective if the zinc primer is able to transfer the galvanic current. Normally it is only the first 20-30 microns of a 60-80 micron zinc epoxy paint layer that are able to give this protection. This is because the epoxy resin acts as an insulator to the zinc particles causing them to lose their galvanic properties. Even with a high zinc content, around 80 percent of the zinc will be too far away from the point of corrosion to be of any use.

Avantguard technology solves this problem by activating more of the zinc throughout the coating to enhance its effectiveness. It does this through the introduction of hollow glass spheres and a proprietary activator, which are combined with a mix of binders, pigments, fillers and additives. The result is significantly greater protection over longer periods.

Enhanced protection
Once the zinc becomes more active, the process causes a layer of insoluble salts to form on the surface of the coating, and within the film, which acts as an effective barrier against water permeation. This is a significant advantage as traditional zinc epoxies generally exhibit a low level of water resistance. Increasing the barrier against water penetration enhances the lifespan of the coating.

Chloride ions found in marine or coastal environments will cause pitting corrosion to steel structures. Avantguard technology effectively captures these ions by forming chloride-containing salts around the hollow glass spheres. This delays the corrosion process as the chloride ions are trapped within the coating and prevented from reaching the steel surface.

Fluctuations in temperature together with potential mechanical stress is a consideration for Elco and it is important that the chosen coating can manage these impacts without cracking or flaking. Fortunately, Avantguard technology compensates for this through its unique self-healing properties. The hollow glass spheres within the primer absorb much of the energy should micro-cracking occur thereby preventing initial cracks from widening and developing. In addition, the subproducts formed by the zinc activation process tend to occupy the space left by micro-cracks and prevent them from developing into something more serious. This significantly reduces rust creep and ensures that the coating maintains its anti-corrosive performance for much longer. 

Easy applicationElco was keen that its chosen coating was easy to apply in high levels of temperature and humidity. It found that Hempadur Avantguard did not blister in the extremes of temperature found at the application facility and that the re-coat interval was much shorter than traditional zinc rich epoxy primers. Additionally, its high dry film thickness is not susceptible to cracking which means that Elco’s operators needn’t be overly concerned when applying to welds or in corners where over-application tends to occur.

For the companies working in the aggressive environment of the Khazzan gas field, the advantages of utilising Hempel’s innovative Avantguard technology can be significant. In general, the enhanced anti-corrosion protection should increase the lifetime of the onsite assets and reduce maintenance requirements and costs. Avantguard’s wide tolerance gives Elco the option to touch-up and repairs a coating on site and, since it is easier to apply than other primers and enjoys a shorter recoat interval, application speed and efficiency is improved.

Through Hempel’s work in redefining anti-corrosion paint technology, Elco is now able to reduce rust creep, enhance resistance to corrosion, improve crack resistance and heighten the tolerance of the steelwork it has installed in this extremely demanding environment.

Author: Simon Daly is Oil and Gas Segment Manager at Hempel A/S.

© Chemical Today Magazine

Read More: Protecting steel structures in a demanding environment