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Collaborating Authors
Well Completion
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. INTRODUCTION 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.
- Geology > Mineral (1.00)
- Geology > Sedimentary Geology > Depositional Environment > Marine Environment (0.61)
- Water & Waste Management > Water Management (1.00)
- Materials (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
Life Time Assessment of Offshore Water Injection Pipelines As a Function of Microbiologically Influenced Corrosion
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 INTRODUCTION 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).
- Europe > United Kingdom > North Sea (0.45)
- Europe > Norway > North Sea (0.45)
- Europe > North Sea (0.45)
- (4 more...)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Oil & Gas > Midstream (1.00)
- Water & Waste Management > Water Management > Lifecycle > Disposal/Injection (0.77)
ABSTRACT: Carbon steel pipelines are used extensively in the oil and gas industry for sub-sea applications. Usually they are cathodically protected and have exterior surface protective coatings. Where these are ineffective or not used, the evolution of weld zone corrosion with time may be of interest. Experience has shown that generally the heat-affected weld zone is more severely corroded by pitting than either the weld zone itself or the parent metal. However, quantitative data are scarce, particularly for longer-term exposures. Herein observations are reported of the pitting corrosion of API X56 Spec 5 L grade pipeline steel exposed continuously to natural Pacific Ocean seawater for 3.5 years, and extended to much longer exposure periods by comparison to similar steels exposed for up to 30 years. It is shown that the corrosion mass loss, maximum pit depth and pit depth variability are not simple linear functions of exposure time as often assumed in practice but are more complex functions. These functions are consistent with those observed previously for mild steels in various marine exposure conditions. However, considerable differences were noted in severity. The reasons for this are discussed and further work is outlined. INTRODUCTION Carbon steel pipelines are used extensively in the offshore oil and gas industry. This is important for the exterior of pipelines. Internally oil pipelines may be subject to carbon dioxide and hydrogen sulphide corrosion, depending on the condition of the oil flowing through the pipe and also to much greater local corrosion at the base of the pipe (6 o'clock position) if the water cut of the crude oil is high and flow velocities low. Water injection pipelines, on the other hand, typically have high water content but low or negligible oil content and very low oxygen levels and are often subject to microbiologically influenced corrosion (MIC).
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Piping design and simulation (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
Investigation of Severe Corrosion of Mooring Chain In West African Waters
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)
ABSTRACT Recent detailed observations of the performance of mooring chains for a floating production unit in tropical West African waters have shown severe localized corrosion (pitting) of the steel chain after only seven years of use. This paper describes the investigation of this phenomenon as part of the Joint Industry Project (JIP) research program SCORCH (Seawater Corrosion of Rope and Chain) funded by the major oil companies, most Classification Societies and various offshore operators and manufacturers. It is shown that there is a high likelihood that the chain has been subject to microbiologically influenced corrosion (MIC) as a result of the elevated levels of water pollution in the operational area. However, despite the large localized loss of steel in corrosion pits, the breaking load shows only a relatively small reduction compared to the Minimum Breaking Load specified in design guidelines. INTRODUCTION The SCORCH (Seawater Corrosion of Rope and Chain) project is a Joint Industry Project (JIP), funded by the oil industry, for research into the corrosion of steel chain and wire rope as used in the offshore industry for mooring large floating platforms used for storage, production and offloading of oil, particularly in deeper waters. The JIP also will develop improved guidelines for offshore operations involving chain and wire rope. The vessels are either specially built or can be converted oil tanker ships (often minus propellers and rudder). In many cases they are moored to the sea floor using mooring system of 5 or more lines. These are connected to the vessel at a bow-mounted turret (or similar arrangement). Disconnection is possible in the event of a tropical cyclone threatening the vessel. Each mooring line typically is a series system, commencing at the vessel with a heavy-duty high-tensile steel chain. It runs through the splash zone into the immersion zone where typically it connects to galvanized wire rope (for deep waters).
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Mooring systems (1.00)
Abstract 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.
- North America > United States > Texas (0.28)
- Europe > United Kingdom > North Sea (0.25)
- Europe > Norway > North Sea (0.25)
- (2 more...)
- Water & Waste Management > Water Management > Lifecycle > Disposal/Injection (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Abstract 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. Introduction This paper summarizes some of the on-going work by the SCORCH JIP oncorroded/pitted chain links that were recovered from a Floating StorageOffloading (FSO) system based in West Africa. Although these links were inservice for only seven years, they experienced severe pitting corrosion (Figure 1) not noted previously in any available records. In some cases the pittingcaused a reduction in cross-sectional area of 35%. The chain links, whichexhibited strong signs of corrosion, were donated by the operator to the JIPfor research. They were shipped to Vicinay Cadenas in Spain for examination andtesting. This was performed according to the SCORCH JIP examination procedure. It is designed to gather all information required to perform a scientificanalysis in order to explain the observed corrosion. The FSO and its mooring system were installed in shallow water offshore WestAfrica in 1997. The external turret mooring system used a 6-leg all-chaindesign. The mooring chains were not isolated from the vessel hull, and thusmight have had some limited coverage by the Impressed Current CathodicProtection (ICCP) system on the vessel. The mooring legs consist of foursections, provided by three different vendors (numbered 1 to 3), as illustratedin Figure 2. Initially, there were three segments, a top and a bottom sectionprovided by the same vendor, with a catenary inflection weight (CIW) insertedto increase clearance and avoid clashing with the bow. Section 2 hangs from theCIW, serving as a clump weight. Section 3 was inserted between the CIW and theground chain when the FSO was relocated to a slightly deeper water depth. Allthree types of chain are 76mm in diameter. An early hypothesis theorized thatthe dissimilarity of the three materials was the root cause of the observedsevere pitting corrosion. The present investigation disproves thishypothesis During the annual chain survey in 2005, some visible corrosion on the chainsimmediately above waterline was noted. To determine the extent of metal loss, rope men were sent down to measure those chain links in air using a caliper. The survey showed that the in-air links had lost some cross-sectional area, apparently due to the well-known splash-zone effect [5]. Their remaining areaswere still within allowable limits at that time. During inspection in 2007, pitting corrosion was observed for the first time during a diver inspectionafter heavy marine growth was removed (see Figure 3). However, the extent andseverity of the problem was not evident at the time. In 2009, a decision wasmade to change out the mooring system. When all chains were recovered to terrafirma and marine growth was removed, it was found that the condition of thesubmerged chains was as poor as the splash-zone chains, although the damage wasof a different form.
- Africa > West Africa (1.00)
- North America > United States > Texas (0.28)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Mooring systems (1.00)