This paper reviews recent developments in the prediction of the likely future corrosion losses and of the maximum pit depth for steels exposed to marine environments. A robust mathematical model based on corrosion science principles and calibrated for immersion conditions to an extensive range of literature and new data is described. The model has provided explanations for the effects of steel composition, water velocity, depth of immersion and seawater salinity and also has facilitated new interpretations of data for long-term pitting corrosion. This paper briefly overviews these developments and refers to some typical applications, including marine corrosion of ship ballast tanks, corrosion of sheet piling in harbours and corrosion of offshore platform mooring chains.
Physical infrastructure plays a major role in the most modern societies. So-called whole-of-life assessments increasingly are being used for decision processes. Such algorithms require models of sufficient rigor and robustness to represent (a) the demands or loadings expected to be placed on the system; (b) the ways in which the system may respond; and (c) prediction of likely future response, including deterioration and effectiveness of repairs. Consistent with modern decision theory, the models required for (a) and (b) are probabilistic (Melchers, 1998). Until recently, models for (c) were largely ignored. Most infrastructure has expected lives of several decades. As argued previously (Melchers, 2005), the only way such predictions can be made is to invoke a combination of scientific understanding of deterioration processes and sound mathematical modeling. The present paper is concerned with the development of corrosion models, particularly for longer-term exposures. Despite good maintenance regimes, and the availability of protective coatings and of various forms of cathodic protection, field evidence shows that existing infrastructure often shows signs of corrosion, particularly in severe environments, such as for offshore facilities, along marine coastlines and in harbors.
Comanescu, Iulian (Corrosion in aggressive environments, Swerea KIMAB AB) | Melchers, Robert E. (Centre for Infrastructure Performance and Reliability, The University of Newcastle) | Taxen, Claes (Corrosion in aggressive environments, Swerea KIMAB AB)
Corrosion of water injection pipelines (WIP) in the oil and gas industry is a major issue involving potential premature life time predictions and unpredicted costs like periodic biocide treatment and pipeline pigging. This paper presents a part of a larger project concerned with improving understanding of the influence of bacterial activity on corrosion, as distinct from abiotic corrosion, in oil and gas transport systems for better management of pipeline systems. Observations are made concerning life time as a function of microbiologically influenced corrosion (MIC) risk and relationships between MIC, bacterial numbers and types, and water quality
Accurate prediction of pipeline lifetime is of major importance for operators and owners. To obtain adequate prediction of the expected lifetime for a line it is necessary to know the root causes of possible failures and how often failures occur. The main root causes how to be measured in place to mitigate problems as they arise. In order to achieve this “Classification Societies” and “Oil Companies” have invested and continue to invest a lot of time and money to obtain the necessary knowledge for preventing future failures. Reports and recommendations such as PARLOC (2001) and DNV (2006) now are available to help identifying the most common failure causes, and how to prevent future accidents. In DNV’s (2009) “Recommended Practice” document they concluded that in Gulf of Mexico corrosion represents about 40% of the total numbers of failures resulting in leakages. Internal corrosion represents 81% of the corrosion failures. For the North Sea pipelines corrosion failures represented 27% of the total number of failures and internal corrosion was the major cause. It is evident that the main problem for pipelines both in the North Sea and in the Gulf of Mexico is the result of internal corrosion (DNV 2009).
Fontaine, Emmanuel (AMOG Consulting Pty Ltd) | Potts, Andrew. E. (AMOG Consulting Pty Ltd) | Melchers, Robert E. (Centre for Infrastructure Performance and Reliability, The University of Newcastle) | Arredondo, Alberto (Vicinay Cadenas) | Ma, Kai-tung (Chevron Energy Technology Company)
The present study compares corrosion mass loss and pit depth measurements on carbon steel corrosion coupons exposed under similar operating parameters, but with different biological consortia. One set of data were obtained from standard flush disc corrosion coupons used to monitor corrosion rates in a water injection pipeline on the North Sea continental shelf. The coupons were exposed on average for 6 months over 6 years operational time. These data are compared with published corrosion data of coupons exposed in abiotic district hot water systems from several power plants situated in Europe. The exposure time for these coupons was 9 months. Both systems were anoxic and in the same temperature range and are comparable. Observations regarding relationship between MIC and bacterial consortia, bacterial numbers and type, water quality and corrosion products are also made.
The corrosion rate of the water injection pipeline is approximately 10 times higher compared with the corrosion rate in the abiotic district hot water system. It is concluded that the increased corrosion on the carbon steel coupons in the early stage is caused by MIC. This is also supported by the chemical and biological information available for the pipelines. The results reported here constitute the first step of an overall study to improve the level of understanding of the bacterial contribution to the total corrosion rates of carbon steel in water injection flowlines.
Such understanding is expected to improve management and operational decision-making for practical control of corrosion in the field, by providing predictions of expected life time as a function of control of biotic consortia (e.g. through pigging, and biocide treatments). Further, it will facilitate decisions concerning choice of pipeline construction materials for future design.
Fontaine, Emmanuel (AMOG Consulting) | Potts, Andrew (Chevron Corp.) | Ma, Kai-tung (Vicinay Cadenas S.a.C) | Arredondo, Alberto (Centre for Infrastructure Performance and Reliability) | Melchers, Robert E.
The paper describes a forensic investigation performed on severely corroded(pitted) chains recovered from a FSO mooring system in West Africa. During theinvestigation, it became apparent that a similar phenomenon had beenexperienced by JIP participants operating at other locations in West Africa,indicating that it may be a common problem deserving attention. The tentativeconclusion of the present investigation is that the large pits most likely canbe attributed to Microbiologically Influenced Corrosion (MIC). Subsequent pulltests of the chains to determine their residual strength gave surprisingly goodresults. Despite the large reduction in cross-sectional area, the effectivebreaking loads of the tested samples were found to be around 80-90% of thecatalogue minimum breaking load (MBL). The results also showed the chain linksto be resilient in strength.