Protecting steel structures in the oil and gas industry from corrosion

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1 Protecting steel structures in the oil and gas industry from corrosion Developing new galvanic protective coatings to limit impact upon project coating schedules. Oil and gas asset owners are increasingly looking for longer performance from their corrosion protection methods, but at the same time wish to reduce their overall capital expenditure budget in all areas. Protective coatings offer a viable solution to many corrosion challenges found in the oil and gas industry and millions of litres of paints are used to protect these assets globally. However, the protective coatings industry has been faced with many challenges in recent years and has had to wrestle with: how to reduce impact on project schedules brought about by late-stage painting activities, how to minimise delays due to painting rework and in-service failures, and, how to maximise the cost effectiveness of time spent on painting activities. Galvanic coatings are coatings containing metal particles that are non-noble relative to the ferrous substrate. These coatings form a physical barrier and act as a sacrificial anode when the barrier is damaged. Zinc-containing paints may be considered galvanic coatings. New galvanic coatings based around organic zinc epoxy resins can significantly improve the productivity of painting activities during project construction. As galvanic coatings often represent part of the largest painting scope on onshore capital projects, savings made here can offer significant benefits in terms of improved productivity and subsequent reduced painting costs. Historically, zinc-containing paints or protective coatings have been divided into two types; inorganic zinc coatings based around ethyl silicates, and organic zinc coatings based around epoxy resins

2 In both cases the zinc is present in the form of zinc dust particles. The amount of zinc present plays a key role in determining the degree of corrosion protection provided, with more zinc dust present in the final coating film generally leading to reduced corrosion creep when tested in simulated corrosion-inducing environments (although other factors also play a part). The level of zinc present is prescribed in a number of standards such as ISO : 2018 and Steel Structures Painting Council document SP 20. The two types of paint also differ in their intended uses. Whist inorganic coatings, due to the presence of their silicate backbone, can be used to provide corrosion protection across a wider range of temperatures (typically up to 400 C), epoxy zinc coatings are limited to providing corrosion protection across a more limited temperature range (usually no more than 120 C) due to their organic backbone. On the face of it, inorganic zinc-based paints offer a better option and indeed have historically been found to offer the best level of corrosion protection of the two categories when comparing products with like-for-like zinc content. However, inorganic zinc coatings have some significant drawbacks when used for steel protection. 1 Ideal application conditions for a solvent borne inorganic zinc galvanic coating is C (68 to 77 F) with a relative humidity (%RH) between 50 and 90%. Painting in conditions outside of this can significantly increase drying time and reduce productivity. 2 Solvent borne inorganic zinc silicates have a tendency to mud-crack when applied too thickly, leading to rework costs. Minor mud-cracking that is tightly adherent may not necessarily be detrimental, however visible mud-cracking may be cause for alarm. This may further hinder drying due to the thicker film. 3 The porous nature of the zinc in an inorganic silicate binder may cause gassing or pin-holing of subsequent coats. Techniques to minimise this involve the use of a mist coat which may lead to longer application times. Failure to address the issue proactively, however, may lead to subsequent repainting activities and incurred costs.

3 Given all of the drawbacks, why are inorganic solvent borne zinc-based coatings so widely specified and used? The answer lies in their excellent corrosion protection and their ability to protect ferrous substrates, which traditionally has been considered superior to organic equivalents when comparing products with similar levels of zinc dust present. However, recent advances in organic zinc epoxy galvanic coatings offer significant construction benefits, whilst offering comparable corrosion protection. In the case of these improved organic zinc epoxy galvanic coatings, the contribution to the galvanic effect is believed to be not simply restricted to the substrate, as the coatings have a higher ability to release electrons, creating a more efficient anode. X-ray section after 1000 hours simulated corrosion testing (salt spray, 35 C, NaCl 50 g/litre). Insoluble zinc salts are coloured green. The performance advantages can be clearly seen when looking at the zinc containing galvanic coating when used as a primer only (overleaf).

4 Inorganic zinc silicate galvanic coating New organic zinc epoxy galvanic coating Traditional organic zinc epoxy galvanic coating Above: Simulated corrosion testing using salt fog exposure for 5 months (3600 hours). Coatings are all applied at a dry film thickness of microns. Further performance advantages in terms of higher resistance to cracking of the paint film can also be seen. New organic zinc epoxy galvanic coating Inorganic zinc silicate galvanic coating Evaluation of cracking resistance according to National Association of Corrosion Engineers (NACE) standard TM thermal cycling resistance test. Both samples were tested at 160 microns. The new coating shows significantly improved crack resistance.

5 Improving paint productivity Paint productivity can be significantly increased by switching to the new type of organic zinc epoxy galvanic coatings by: elimination of interim mist coat operation faster drying times across a wider range of climatic conditions shorter minimum overcoating intervals no need for additional wetting or accelerator components which require additional mixing and control in the case of low humidity construction locations 5 hours of time savings to apply a typical 3-coat paint scheme can be realised by switching to the new organic zinc epoxy galvanic coatings when compared to typical inorganic zinc silicate coatings in the market. Hempel coating system based on Hempadur Avantguard 860* Typical IOZ based system in the market** Time saving up to 5 hrs Primer Mid-coat Topcoat st Shift 2nd Shift Primer *Based on Hempel System Avantguard 860 / Hempaprime Multi 500 / Hempathane HS **Based on generic 3-coat system with fast curing IOZ as primer under optimum curing conditions (25 C / 77 F and RH > 50%. Increased overcoating intervals for lower temperatures and humidities may occur) Conclusion Recent advances in organic zinc epoxy galvanic coatings offer significant construction benefits over inorganic zinc silicates, such as reduced repair work due to a higher resistance to cracking, as well as comparable corrosion protection. Hempadur Avantguard 860 represents a new organic zinc epoxy type of galvanic coating available from Hempel A/S. It is part of the Avantguard range of activated zinc epoxy primers. For further details please contact lamu@hempel.com Hempel A/S 2018 The Hempel Group Head Office Hempel A/S, Lundtoftegaardsvej 91, 2800 Kgs. Lyngby, Denmark Tel: lamu@hempel.com hempel.com