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Corrosion Behaviour of Ni-Cr Alloys in Oxygen at High Temperature

Paper Number: 68
Author/s: Y.L. Hsu, Y. Xie, J. Zhang
Organisation: School of Materials Science and Engineering, University of New South Wales, Sydney NSW 2052, Australia

Abstract

To meet an increased energy demand, it is necessary to increase steam turbine operating temperature of coal-fired power plant from conventional practice of 540°C to ultra/advanced ultra-supercritical practice over 700°C. Because of this temperature increase, traditional ferritic/martensitic and austenitic steels cannot survive. Instead, nickel- base alloys have to be used because of their superior creep strength and steam oxidation resistance at high temperatures.

In this work, oxidation behaviour of binary Ni-Cr alloys with Cr concentration from 5 to 30 wt% was investigated in 20%O2-80%Ar gas for up to 310 h reaction at 650, 700 and 800 °C. All samples were electro-polished to avoid the accelerated alloy Cr diffusion due to the effect of surface cold work. The results showed that for Cr concentration lower than 30 wt%, all alloys formed a multi-layered oxide scale, together with an internal oxidation zone. Increasing Cr concentration to 25 wt% led to the formation of a chromia band at the reaction front and a significant reduction in internal oxidation zone. When Cr concentration reached 30 wt%, a thin protective chromia scale was observed at all temperatures. The effects of chromium and temperature on oxide formation were discussed based on reaction kinetics and diffusion analysis during high temperature reaction process.

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The study of water-line corrosion in static and dynamically flowing electrolytes using multi-electrode sensor in combination with electrical resistance method

Paper Number: 34
Author/s: Yunze Xu1, 2, Mike Yongjun Tan1* and Yi Huang2
Organisation: 1School of Engineering and Institute for Frontier Materials Deakin University, 75 Pigdons Road, Waurn Ponds, VIC 3216, Australia 2School of Naval Architecture and Ocean Engineering, Dalian University of Technology, 2 LingGong Road, Dalian, Liaoning 116024, China

Abstract

In this work, a new sensor system was developed based on an integrated multi-electrode technique in conjunction with an electrical resistance (ER) method. This new method has allowed galvanic currents flowing among the multi-electrodes and the total metal loss simultaneously measured. On the basis of the new designed 10 elements sensor system, the water-line corrosion in both static and flowing electrolytes were studied. It is found that in the static 3% NaCl aqueous condition, the major anodic area is located at the bot
tom of the sensor suggesting the water-line corrosion is controlled by the oxygen differential cell. However, in the flowing condition, the major anodic areas were close to the water line and the bottom region transferred to a cathodic area, suggesting that the flowing of the electrolyte is an important influence factor of the water-line corrosion. From the comparison of the galvanic current and the ER measurement results, it is seen that galvanic corrosion is the main contribution of the water-line corrosion in both static and flowing electrolytes.

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No one cares about the paint – a specifier’s perspective

Paper Number: 45
Author/s: O. Duyvestyn & K. Wilson
Organisation: Advanced Materials & Strategic Asset Management - AECOM Australia Pty Ltd

Abstract

This presentation will light-heartedly discuss topics to specifically address issues that are of interest to protective coating manufacturers and will offer a unique insight into the inner workings of large engineering firms with respect to materials selection and the preparation of protective coating specifications. An explanation will be offered why some specifiers in large engineering firms often get it so wrong, why there is limited attention to detail and where the coating specification ranks in terms of importance within the big picture of the project at hand. The presentation also high-lights how the interaction with coating manufacturers is often perceived, if and how they can influence the independent specifier and discusses the real importance of a manufacturer having their product listed in project specifications. Finally, the presentation addresses the relationship between the specifier and their asset owner client, what drives that relationship and where coating manufacturers fit in that relationship. With this presentation, the presenters intend to provoke a debate between the different parties that need to come together to deliver an outcome that is ultimately in the interest of the end user of applied protective coating systems rather than other parties involved in a new construction or maintenance project.

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Recent Progresses in Understanding Pipeline Coating Degradation

Paper Number: 8
Author/s: M. YJ Tan*, Fariba Mahdavi and Shyama D. Ranade
Organisation: Institute for Frontier Materials and School of Engineering Deakin University, Victoria 3220, Australia

Abstract

The durability and performance of organic coatings, which are widely used for mitigating corrosion of high pressure oil, gas and water pipelines, are known to be affected by cathodic protection (CP), mechanical stress and the corrosive environment. This paper presents our research findings on the impact of CP and the environment on organic coatings under simulated underground pipeline conditions. Coating’s corrosion resistance, disbondment and electrochemical properties have been assessed using electrochemical, surface analytical and computational modelling techniques such as the electrochemical impedance spectroscopy (EIS), optical microscopy and scanning electron microscopy, X-ray computed tomography and finite element analysis. In situ and ex situ scanning electron microscopy was employed to trace and characterise coating defects from the very early stages of micro shear bands initiation to the formation of full coating cracks. Finite element analysis has been employed to understand the influence of strain on the initiation and propagation of coating defects by modelling stress distributions. A correlation has been found between the applied strain levels and the corresponding coating resistance and coating capacitance values. The strain distribution and shear stress distribution patterns obtained using the finite element analysis were used to explain typical features observable in EIS data based on the formation of electrolytic pathways through unstrained and strained coatings. This approach has been consolidated into a two and a three dimensional model proposed to explain the electrolyte movement in a coating impacted by applied mechanical strain and environmental exposure. On the other hand, the effect of CP potential on cathodic disbondment of a defective coating has been investigated by monitoring the coating disbondment processes during the exposure of coated electrodes to a corrosive solution. The monitoring of coating disbondment was achieved by in situ measurement of local electrochemical impedance and direct current distributions over a multi-electrode array surface under various levels of CP potentials as well as under open circuit potential (OCP). The effects of CP potential and the environmental conditions on the initiation and propagation of coating disbondment have been quantified based on changes in local electrochemical impedance and current distribution maps. The rates of cathodic disbondment have been found to be highly dependent upon the applied CP potential. This result indicates that the evolution of hydrogen likely played an important role in accelerating cathodic disbondment of the coating, and that the ‘critical potential’ at which the hydrogen evolution becomes a significant and dominant electrochemical reaction is important for cathodic disbondment of coatings. It was also found that once the cathodic disbondment initiated under very negative CP potentials, the disbonded distance would spread at an almost constant rate. These results suggest that a practical method of controlling coating disbondment is to ensure that the applied CP potential is below the ‘critical potential’

 

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The role of bacteria in under-deposit corrosion in oil and gas facilities: A review of mechanisms, test methods and corrosion inhibition

Paper Number: 76
Author/s: E Suarez, L Machuca & K Lepkova
Organisation: Curtin Corrosion Engineering industry Centre (CCEIC), Curtin University, Perth, Australia

Abstract

Under deposit corrosion (UDC) has been identified as a phenomenon responsible for many operation failures, representing a threat to pipelines integrity and seawater injection systems. Despite the recent efforts to define the effects of deposits on corrosion of steel surfaces and their inhibition, the influence of microorganisms in these deposited environments have not been largely addressed. Understanding the effect of microbial activity on UDC is important because microbial cells thrive in deposits resulting in an adverse combination of microbiologically influenced corrosion (MIC) and UDC. Additionally, UDC mitigation constitutes a challenging topic since solid particles can decrease the availability of inhibitor molecules to protect the underlying steel against corrosion. Biofilms comprise a complex array of molecules and microorganisms that can act as organic deposits compromising the performance of corrosion inhibitors. Therefore, is important to evaluate the corrosion inhibitor efficiency in the presence of biofilm-deposits formed on steels surfaces. This document reviews the literature on UDC-MIC mechanisms, testing methods and prospects in the understanding and inhibition of these complex phenomena.

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Effect of Sample Preservation on the Diversity Profile Assessment of Oilfield Microbial Communities

Paper Number: 46
Author/s: S. Salgar-Chaparro & L. L. Machuca
Organisation: Curtin Corrosion Centre, Curtin University, Perth, Australia

Abstract

Microbiological surveys play a fundamental role in diagnosing and monitoring microbiologically influenced corrosion (MIC) threat in oil and gas systems. In the last decades, the microbiological characterization has been mostly carried out by the implementation of traditional growth-based techniques. However, with advances in biotechnology, molecular microbiological methods (MMMs), which are culture-independent techniques, have begun to replace the conventional methods. Currently, MMMs are being increasingly acknowledged as essential identification tools for MIC threat assessment. Diversity profile analysis based in next-generation sequencing (NGS) of the 16S rRNA gene is being used by the industry to help identify and characterize the total microbial community living in oil and gas production systems, which provides information to assess MIC risk or to predict possible MIC mechanisms. Even though MMMs have been included in the NACE standards, standardized protocols for collection, storage and preservation of oilfield samples have not been written. In this study, the effect of sample preservation on the results from 16S metagenomics analysis was investigated. Upon sample collection, microbial community structure presented significant changes as a result of the sample preservation conditions. Samples processed directly on-site showed higher diversity than samples transported to the laboratory for complete processing. Results of this research provide evidence of the importance of sample handling for an accurate microbial characterization and subsequent success in MIC prediction of oil and gas systems.

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Long-term corrosion of steel chains on pacific ocean beach sand

Paper Number: 22
Author/s: M A Watt, R E Melchers & R Jeffrey
Organisation: Centre for Infrastructure Performance and Reliability, The University of Newcastle, Australia

Abstract

The corrosion of steel exposed to seawater and sand is of interest to the offshore industry for oil production and wind farm caisson or platform mooring systems, and also for assessing the deterioration of shipwrecks. Very few data are available, particularly for long-term exposures. The present paper reports observations made recently at Catherine Hill Bay of the corrosion losses for 70mm diam. steel chain exposed since 1913 to immersion, tidal and splash zone corrosion largely whilst lying on local beach sand. The site, on the Pacific Ocean south of Newcastle, was once a coal loading facility and the chains were used to moor vessels while being loaded with coal. Observations show that, except for immersion corrosion, the rate of corrosion is not high. Corrosion tended to be uniform and there was no obvious signs of large pitting as has been observed in some cases elsewhere for mooring chains. The observations are compared with some classical data available for steels buried in sands for up to 17 years, and examined at regular intervals, that show that most corrosion tended to occur in the first 10-15 years after which the corrosion rate declined. There also are some very short-term (5 month) observations that suggest initial corrosion of metals occurs by crevice corrosion immediately adjacent to the sand particles. These observations allow for an interpretation of the new data.

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New NZ Steel Durability Standard

Paper Number: 3
Author/s: W Mandeno1 & R El Sarraf2
Organisation: WSP Opus Wellington, New Zealand1, & WSP Opus Auckland, New Zealand2

Abstract

This new Technical Specification, ‘Durability requirements for steel structures and components’ (SNZ TS 3404:2018) was prepared by Standards New Zealand to give a means of compliance with the durability requirements of the NZ Building Code Clause B2 and the NZ Transport Agency’s Bridge manual.  It both updates and supersedes the corrosion protection requirements in the Steel structures Standard, NZS 3401.1:2009.  It also complements the new structural steel fabrication and bridge design standards, AS/NZS 5131 and AS/NZS 5100.6 respectively, and should be used with the relevant parts of the protective coatings guide, AS/NZS 2312.

 

TS 3404 mostly covers the corrosion protection of structural steelwork exposed to New Zealand’s different atmospheric environments and includes seven corrosivity zone maps with alternative systems for different corrosivity categories according to the designer’s required life to first major maintenance.  Also covered is the protection of structural steel in common non-atmospheric environments.

 

This paper discusses the development and details of this specification.

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Formulation of VOCs Free Surface Tolerant Anti-corrosion Coatings by Epoxy-Thiokol Copolymer

Paper Number: 10
Author/s: Y Li, F Wang, E Tan, X Yin & Y Zhen
Organisation: Advanced Materials Technology Centre, Department for Technology, Innovation and Enterprise, Singapore Polytechnic, Singapore

Abstract

Common commercial epoxy resin diglycidyl ether of bisphenol A or DGEBA was modified by liquid Thiokol with various ratio under different reaction conditions. A series of epoxy-thiokol copolymers were synthesized and applied as main binder in formulation of VOCs free or solvent free anti-corrosion coatings. The effect of resins, curing agent, adhesion promoter, diluents, pigments, fillers, additives, rust inhibitors, anti-rust penetrant were investigated in this work. The adhesive strength, flexibility, 720 hours neutral salt spray, water immersion test were carried out, the result showed this new VOCs free anti-corrosion coating exhibited good adhesion, flexibility, water resistance, and anti-corrosion property, even on not well prepared steel surface. This environmental-friendly anti-corrosion coatings will have prospective application in maritime industry.

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Atmospheric Corrosion of Mild Steel in a Desert Environment

Paper Number: 5
Author/s: R. Jeffrey
Organisation: Centre for Infrastructure Performance and Reliability, The University of Newcastle, Australia

Abstract

Atmospheric corrosion surveys have been extensively conducted and published for urbanised and rural conditions but relatively few results have been reported for moderate terms in desert environments. This paper describes results from a site in far-western Queensland for over seven years. Corrosion loss was between one and two microns / year. Unlike other more corrosive environments there was no noticeable effect of size or orientation of coupons. Of interest was the fact that akaganéite (usually associated with marine conditions) was identified albeit in very small quantities. Trace amounts of SOx, NOx and Cl were detected. Time-of wetness was recorded as 3.3%, rainfall average is 163 mm/y although this can vary substantially, and exposed temperatures range from freezing to almost 60° C. Results are compared with rural and severe environments.