The Critical Role of Protective Coatings and Inspection in Steel Structures  

Steel remains the backbone of modern infrastructure, from bridges and high-rise buildings to pipelines, tanks, and vessels designed for marine environments. Steel’s durability and versatility make it essential, but steel’s natural vulnerability to corrosion poses a serious challenge. Protective coatings serve as the first line of defence against environmental corrosion, ensuring that steel structures achieve their designed service life safely and cost-effectively.

The Importance of Protective Coatings

Corrosion is a costly and constant threat and the World Corrosion Organisation (WCO), estimates global corrosion costs in the trillions of US dollars annually, with a significant portion of this share absorbed by infrastructure owners. This high cost highlights the critical need for effective corrosion prevention and mitigation to safeguard infrastructure and reduce risk to assets. 

New Zealand Steel structures are designed in accordance with NZS 3404 and coated in accordance with an established standards framework that includes the AS/NZS 2312 series, SNZ TS 3404:2018, AS/NZS 5131 and other relevant standards.

Protective coatings such as zinc-rich primers, epoxy intermediates, and polyurethane topcoatsfunction as engineered systems, and not just aesthetic finishes. Correctly specified and applied coatings mitigate corrosion risks, reduce total lifecycle costs, and extend service intervals, provided that proper maintenance is performed.

The Role of the Coating Coordinator

Even the best coating system will deteriorate if it is not applied or maintained correctly. This is where coating supervision/coordination and inspection plays a vital role. Coating inspectors ensure that surface preparation, environmental conditions, and application processes meet project specifications and international standards. Parameters such as surface profile, measuring and monitoring, film thickness, and adhesion must all be verified.

Through systematic inspection, critical defects such as, checking, blistering or improper curing can be identified and rectified before they lead to premature coating failure. Inspection provides the quality assurance that the protective system will perform as designed.

Certification and Quality Management Systems

AS/NZS 5131:2016 Structural steelwork – Fabrication and erection establish coating requirements as an integral part of the quality management framework for steel construction. The Standard recognises that protective coatings are not an isolated activity but a critical quality element that alongside ISO 3834 – Quality requirements for fusion welding operate in complementary areas of quality assurance for steel structures, and when integrated with coating applications, the fabricator is well positioned to enhance durability, safety, and compliance with the design life of the structure.

Clause 10.6.1 and Appendix I (Surface treatment and protective coating) specify that: Surface preparation and coating application must be carried out under competent supervision, and Inspection shall be performed by a competent person in accordance with the project’s coating specification and referenced standards (typically AS/NZS 2312 series or SNZ TS 3404).

The Standard defines “competent person” (Clause 1.5.13) as “a person who has acquired through training, qualification or experience, or a combination of these, the knowledge and skills enabling that person to perform a specified task.”

AS/NZS 5131 does not name NACE/AMPP (or any specific certification) explicitly. However, industry practice (and referenced standards such as NZTA S9, SNZ TS 3404, and AS/NZS 2312.1) often recognize NACE/AMPP Coating Inspector as an acceptable qualification demonstrating competence for coating inspection.

Conclusion

Protective coatings are engineered systems and not just paint. They preserve the integrity of steel structures, but only when applied correctly. By supporting ASNZS 5131:2016 Structural steelwork – Fabrication and erection and embedding inspection into quality management systems, coating inspectors deliver an objective technical contribution of compliance, reduce project risk, and offset inspection cost by improving service life. HERA (Heavy engineering & research association) has been actively developing expertise in this area to strengthen industry capability, and a HERA Senior Welding Engineer has recently completed the AMPP CIP Level 1 Coating Inspector course. By aligning coating inspection and fabricationprocesses with ISO 3834, fabricators can translate this fully integrated system intomeasurable value with extended service life, reduced maintenance costs, fewer unplanned outages, and improved safety and environmental protection.