Fitness for purpose of low temperature cure liquid-applied coating systems for pipeline maintenance and repair. Potential revisions to incorporate low temperature cure liquid-applied coating products into Table 1 of CSA Z245.30-14 will be presented along with commentary related to the deviations from the standard.
Chloride induced corrosion is the prime reason for the degradation of embedded rebar in reinforced concrete marine structures. The present study experimentally investigates the effectiveness of traditional two-component epoxy (EPX), and moisture-cure polyurethane coatings (MC) applied on the concrete surface in reducing the rate of chloride ingression compared to the conventional concrete with and without mineral admixtures like fly ash and GGBS. Coatings used in the present study are characterized by XRD, EDAX, FEG-SEM, water uptake, adhesion strength and contact angle tests. Rapid chloride migration tests (RCMT) were conducted on concrete with and without coatings. Resistivity offered against the chloride migration monitored during the RCMT test indicated that concrete with MC shown higher resistivity in the initial period and continued to decrease over the test duration at a faster rate, unlike EPX. The non-steady-state migration coefficients of the concrete cured for 28days and coated with MC and EPX coatings were found to be nearly 22% and 48% of that of concrete with SCM cured for 84days respectively. The study is further extended to monitor the corrosion of rebar embedded in coated concrete subjected to corrosion acceleration until the first crack appeared on an uncoated specimen. Variation in current flow, half-cell potentials recorded during the acceleration test and actual mass loss of embedded rebar estimated by gravimetric analysis are presented in this paper.
Shielding of cathodic protection (CP) by disbonded coatings is considered a “worst case scenario” for external corrosion in the pipeline industry. It has been hypothesized that if coatings were partially permeable to CP, the imbalance between cathodic and anodic reactions would induce a high pH environment under disbonded coatings and that would impede corrosion. However, direct experimental evidence of this process has been limited. Moreover, this line of reasoning is often inversed incorrectly assuming that the only reason for the presence of a high pH environment under disbonded coatings is their partial permeability to CP current.
The recent development of an electrochemical self-validating technique to measure the relatively small ionic currents that could permeate through defect free coatings has shed a new light on the topic. It has been found that most of the commercial pipeline coatings tested in unaged conditions present a CP shielding behavior. Accelerated hydrothermal ageing of fusion-bonded epoxy (FBE) coatings was performed to study the effect of water absorption. Ageing resulted in major plasticization, which increased the conduction of CP current through FBE coatings. However, FBE seems to be partially permeable to H+ and/or OH-, which reduces its ability to form and retain a high pH environment under disbonded coatings. In conjunction, these results thus indicate the extremely limited capability of commercial pipeline coatings to prevent corrosion in case of disbondment.
Splash and immersion zones on offshore installations are areas that are exposed to extremely aggressive environments due to the effects of sea water, tides, wind, waves, and/or ultraviolet radiation. Various certifications such as NORSOK(1) exist to help guide customers select a coating based on its corrosion resistance performance. Despite the necessity of these standards, it is helpful to understand that other properties such as substrate surface and cure conditions can greatly effect performance of the coatings. In this paper, we will compare adhesion of two coatings to different substrate surface conditions while both coatings will be cured in two different environments. Our goal is to investigate the effect of curing environment of coatings on adhesion to the substrate.
NEW NACE Standard Test Method for 2018! This NACE International test method describes a reliable methodology for determining the peel strength of polyolefin-based multilayer pipeline coating systems, generally for coating thickness less than 12 mm (0.47 in). This standard provides a method to measure the peel strength of polyolefin-based multilayer coating systems, such as 2-layer polyethylene coating [2LPE], 3-layer polyethylene [3LPE], 3-layer polypropylene [3LPP], and heat shrink sleeve[HSS] field joint coating. It provides essential information on the quality of the applied coating. This is particularly important for field-applied coatings, of which the application process is significantly impacted by the environmental conditions and the skill set of the field applicators. This test method is intended for use by pipeline operating companies, pipeline owners, pipeline contractors, pipeline inspection services companies, and pipeline coating mills.