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Collaborating Authors
Results
Assessing Fatigue Life of Corroded Mooring Chains Through Advanced Analysis
Wang, Sue (ABS) | Zhang, XiYing (ABS) | Kwan, Tom (Kwan Engineering Service) | Ma, Kaitung (Chevron Corporation) | Li, Zhen (ExxonMobil Upstream Research Co.) | Baker, David A. (ExxonMobil Upstream Research Co.) | Izadparast, Amir (SOFEC) | Farrow, Gary H. (AMOG Consulting) | Potts, Andrew E. (AMOG Consulting) | Nair, Aravind (DNVGL) | Prabhu, Milind L. (Chevron Corporation) | Vargas, Pedro M (Chevron Corporation) | Perez, Imanol Martinez (Principia) | Luo, Meng (Shell International Exploration and Production Inc.) | Fontaine, Emmanuel (iSea Consulting)
Abstract Evaluation of corroded chain link for continued use or life extension is a challenging task for the industry. ABS, together with fifteen (15) participating organizations, initiated the Fatigue of Corroded Chains (FoCCs) Joint Industry Project (JIP) in 2016. The objective of the FoCCs JIP is to investigate methodologies for assessing remaining fatigue life of the corroded mooring chain used for floating production systems. The JIP scope includes fatigue testing in labs and finite element analysis (FEA) of corroded chain samples retrieved from six floating production facilities in West Africa and the North Sea. The participating organizations include oil majors, chain manufactures, consulting firms, and classification societies, which represent a pool of broad range of mooring knowledge and experience. Knowledge gained from the JIP will be summarized and used toward the development of guidance notes for assessing fatigue life of corroded mooring chain for the industry. Six sets of mooring chain samples with different corrosion conditions have been collected, cleaned and digitally scanned for fatigue testing and FEA. Procedures for testing and analysis have been developed with the objective of establishing commonly accepted methods. Different FEA procedures have been studied for making a better prediction of stress ranges of the corroded chain links. The findings from the fatigue testing and FEA will be utilized as basis for further development of the methods for fatigue assessment of corroded mooring chain. This paper summarizes the tests and FE analysis work for the selected chain samples. The JIP research work has found that corrosion, either general corrosion or local/pitting corrosion, can significantly reduce the chain fatigue capacity. The location and the geometry of corrosion pits have more impact on fatigue lives than the pit size. The JIP study has shown that FE analysis is an effective tool to capture the hot spot of corroded chain links and can provide insight in their fatigue performance. Different methods on the assessment of the stress range of a hot spot are compared and discussed.
- North America > United States > Texas (0.29)
- Europe > United Kingdom > North Sea (0.25)
- Europe > Norway > North Sea (0.25)
- (2 more...)
- 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)
The Buoy Supporting Risers (BSR) System: Engineering a Solution for Ultra-Deep Water Subsea Developments in Harsh Environments
Cruz, Ivan (Subsea 7) | Hepner, Gustavo (Subsea 7) | Karunakaran, Daniel (Subsea 7) | Claro, Claudia (Subsea 7) | Nicoletti, Frederico (Subsea 7) | Fontaine, Emmanuel (Subsea 7) | Hesar, Majid (Subsea 7) | de Paula, Marcus Tadeu R. (Petrobras) | Trovoado, Leandro C. (Petrobras)
Abstract The Sapinhoá and Lula North-East fields were developed through pilot systems composed of satellite wells connected to spread moored FPSOs. Each of these developments needed to connect up to 45 lines coming from the wells to a single balcony at FPSO portside, not including gas export riser and its ESDV umbilical. It was expected variable levels of CO2 and H2S, posing the challenge to find a suitable solution that endure the 27 years life of the fields in 2140m water depth in the harsher Santos Basin. To cope with these challenges, Petrobras and partners (BG E&P Brazil and Repsol Sinopec Brazil, in Sapinhoá field, BG E&P Brazil and Petrogral Brazil, in Lula Field) decided to pursue a decoupled risers' system solution and launch a "design competition process" which ended up selecting the Buoy Supporting Risers (BSR) concept solution developed by Subsea 7. This paper describes the BSR System and the needed careful physical and numerical modelling and massive analysis of a largely complex new system, backed up by prototype tank testing, all of them tackled to capture the in-place behaviour to generate the design input envelopes for all system components.
- North America > United States > Texas (0.46)
- South America > Brazil > Brazil > South Atlantic Ocean (0.24)
- South America > Brazil > São Paulo > South Atlantic Ocean (0.24)
- South America > Brazil > Brazil > South Atlantic Ocean > Santos Basin (0.99)
- North America > United States > Texas > Fort Worth Basin > Overall Field (0.99)
- South America > Brazil > São Paulo > South Atlantic Ocean > Santos Basin > Block BM-S-9 > Sapinhoa Field > Guaratiba Formation (0.94)
- (6 more...)
- 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 > Risers (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Mooring systems (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Floating production systems (1.00)
Abstract The paper presents a new subsea structure foundation concept and installation method, called the post-installed mudmat. With this new method, the thermal expansions and displacements of HP/HT flowlines are no longer limiting criteria for the subsea structures. It is applicable to the pipeline end termination (PLET), either first end or second end, and In-Line Tee structure to be laid in any mode (S, J or Reel lay). Combined with Subsea 7 experience of installing structure in all modes, the study is based on computer works to verify the installation sequence, the pipeline integrity and the geotechnical strength. The post-installed mudmat concept is applicable to the projects where the pipe laying method includes structures. In the present application, the pipeline is laid in standard S (also applicable to J or Reel lay) mode with a piping module, including valve and connectors, going through the vessel tensioners and stinger also called firing line. Generally two mudmat wings are added before reaching the stinger and then unfolded subsea. In the new method, a purposely designed mudmat and associated devices is post-installed at sea-bed level on top of a previously laid simple pipeline and module. The specific mudmat guiding and securing device allows the pipe module leveling and weight transfer before the mudmat fulfills its foundation functionality. Comprehensive computer simulations have been performed to verify the laying of pipe module and the new post-installed mudmat on the sea-bed. Calculations confirm the integrity of the pipeline at anchor point to the mudmat after installation. Geotechnical simulations also verify the piping module temporary bearing and the final foundation capacity and settlement. The post-installed mudmat design brings a significant contribution to the pipeline laying method. The mudmat size is no longer a limiting parameter for its integration in the main line. Compared to its opposite design, the pre-installed mudmat, it is not impacted by the installation tolerances which would make it larger and longer. It can also be fixed, sliding or fitted with rails to accommodate the pipeline thermal expansion without significant impact on the piping module design going through the main line. It presents an alternate to other method with separate deployment table generally retained for PLETs or In-Line Tees too large for the standard main line. This post installation process is patent pending.
Abstract Forensic investigations on severely corroded (pitted) chains recovered from the mooring systems of two FPUs in West Africa and Indonesia are described. During the course of the SCORCH JIP, it became apparent that a similar phenomenon had been experienced by other JIP participants indicating that it may be a common problem deserving attention. The conclusion of the present investigation is that the large pits most likely can be attributed to Microbiologically Influenced Corrosion (MIC). Where pitting occurred, the pit depth growth rate was found in instances to be up to 10 times the uniform corrosion rate, with pits distributed approximately uniformly but randomly around the link and the bar circumference. Destructive tensile tests of the samples indicated residual strength that was at worst 25% below as-manufactured estimated As-new Breaking Load (ABL). The correlation of loss of strength with loss of metallic area due to uniform and pitting corrosion indicated that breaking load cannot be treated simplistically, and requires more sophisticated consideration of the pit geometry and its location with respect to areas of high stress within the link.
- 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)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Mooring systems (1.00)
SCORCH JIP - Feedback from Field Recovered Mooring Wire Ropes
Rosen, Jeremy (AMOG;) | Potts, Andrew (AMOG;) | Fontaine, Emmanuel (AMOG;) | Ma, Kai-Tung (Chevron Corp;) | Chaplin, Richard (University of Reading;) | Storesund, Walther (DNV)
Abstract Forensic investigations performed as part of the SCORCH JIP on wire ropes that were recovered from FPU mooring systems from Indonesia and Thailand are described. These wire ropes were used in tropical seawater for operating periods ranging from 9 to 14 years before being replaced for various reasons, including corrosion and fatigue concerns. The observed degradation mechanisms within the wire ropes are summarised and the severity of degradation is assessed in view of the external conditions (load duty, direct environment – sea water or mud), sustained by the rope and the rope construction (6-strand and 8-strand). Residual break tests were performed on 7 of the recovered wire rope samples. Mooring design codes pertaining to the corrosion endurance of steel wire ropes are reviewed with respect to recommendations for galvanic coating thickness and lubricant/blocking compound. The results for the recovered wire ropes from tropical waters are compared with reported zinc dissolution rates from cold North Sea waters.
- Asia (1.00)
- North America > United States > Texas (0.28)
- Europe > United Kingdom > North Sea (0.25)
- (3 more...)
- 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 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)