Abstract

A team assembled by a major oil company designed a test program to assess the difference in coating performance between dry abrasive blasting and Waterjetting as surface preparation methods. They were also interested in determining whether using flash rust preventing, decontamination chemical in conjunction with various applications had any effect on coating performance. A glass flake epoxy was used. Panels were treated with 262 MPa (38,000 PSI) Waterjetting, Dry Garnet Blast + Power wash, in both cases with and without a decontamination chemical. Another set of panels was sprayed with ASTM D11413 seawater salt spray after treatment and then coated.

The 300 mm X 600 mm coated panels were saw cut into smaller panels. Some were subjected to per ISO 203401 Ageing Procedure Annex A and ISO 2812-25 Seawater Immersion. Others were submitted to ASTM G 504 long-term field exposure test over 5 years. In both cases, when the decontamination chemical was used, no significant difference in coating performance was detected, including in panels exposed to light seawater mist spray before coating application. The scribed waterjetted panels exhibited more undercreep than abrasive blasted panels, but this undercreep only began to develop after two years.

Introduction

The Problem

Offshore assets such as drilling rigs, production platforms, and wind turbines present challenges for corrosion prevention maintenance. The primary defense against atmospheric corrosion on structural steel in offshore saltwater environments is a protective coating system.

Several factors cause protective coatings to degrade rapidly: besides wearing and damage encountered in installation and use, ultraviolet light breaks down the organic resins and corrosive seawater causes under creep at any breaks in the coating. Maintenance coating for offshore atmospheric systems can therefore be necessary as early as the second year.

However, a practical challenge occurs in the maintenance process. On offshore structures space is limited and very expensive. Priority goes to crews operating and maintaining drilling or production equipment, and providing housing, food, living, and working space for them. There is little extra space for personnel or equipment that perform occasional maintenance activities like painting. Thus, procedures that reduce the amount of equipment or supplies required, or otherwise reduce the strain on the limited space on offshore structures provide a benefit to operators.

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