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Collaborating Authors
He, Haiping
High Manganese Steel HMS Technology for Mooring Chains Application
Verma, Neerav (ExxonMobil Upstream Research Company) | Wasson, Andrew (ExxonMobil Upstream Research Company) | Li, Zhen (ExxonMobil Upstream Research Company) | Sidhar, Harpreet (ExxonMobil Upstream Research Company) | Yue, Xin (ExxonMobil Upstream Research Company) | He, Haiping (ExxonMobil Upstream Research Company) | Jin, HyunWoo (ExxonMobil Research and Engineering Company) | Ling, Shiun (ExxonMobil Research and Engineering Company) | Jun, HyunJo (ExxonMobil Research and Engineering Company) | Ozekcin, Adnan (ExxonMobil Research and Engineering Company)
Abstract Oil and gas industry experiences indicate mooring chain corrosion is a major challenge. Observed corrosion rates in the field can be several times higher than the design allowance. In addition, pitting corrosion is not considered in design but can be significant in service. Pre-emptive chain replacements may be required which are typically very costly. In addition to corrosion, some of the other performance factors for mooring chains include strength, wear resistance, toughness and fatigue resistance. Carbon steel is the conventional material currently employed for mooring chains. There are significant incentives to develop new material technologies with improved seawater corrosion and wear performance for mooring chain application. This paper describes one such new material technology โ High Manganese Steel (HMS), and its assessment for mooring chain application. HMS is a family of alloyed steels that, when optimized, can offer improved properties over conventional carbon steel. Several HMS chemistries were manufactured, on which small scale performance evaluation testing and weldability assessments were carried out. Based on the assessments, these custom HMS alloys show promising results in terms of the performance factors required for mooring chain application.
In this paper, the authors present a finite element analysis (FEA)-based methodology for estimating the residual strength of degraded mooring chains. The paper presents work investigating FEA modeling parameter sensitivities and selection of appropriate parameters for FEA modeling. In addition, validation against break testing of full-scale chains is presented. Introduction A typical offshore (e.g., floating production storage and offloading (FPSO)) mooring system may contain multiple components: chain stopper, fairlead or bending shoe, chain segments, wire rope, polyester rope, sockets, thimbles, anchors, and connectors or jewelry of various types. Because of its robust nature, chain is usually used at locations along the mooring line that are prone to the highest damage, such as at the top under high tension and in the touchdown or โthrash zone.โ Two types of chain may be considered for mooring systems: studded and studless. Studded chains have a stud, or brace, placed between the bars in the midsection of the chain to prevent flexure and aid in fatigue endurance. Studless chains do not contain a bracing stud.
- Europe (0.68)
- North America > United States > California (0.46)
- North America > United States > Texas (0.28)
ABSTRACT The safe operations of floating production assets rely on the integrity of the mooring system. Mooring systems are exposed to vessel motions and a seawater environment, both of which influence chain degradation. As such, mooring system designs account for a projected amount of degradation through selection of chain size, but all degradation modes may not have been foreseen and/or the actual degradation rates may be higher than anticipated in the design. In these situations, an immediate concern is understanding the integrity of the mooring system and then determining the time frame needed to safely manage the mooring system life cycle. In this paper, the authors present a finite element analysis (FEA) based methodology for estimating the residual strength of degraded mooring chains. The paper presents work investigating FEA modeling parameter sensitivities and selection of appropriate parameters for FEA modeling. In addition, validation against break testing of full-scale chains is presented. INTRODUCTION A typical offshore (e.g. Floating Production Storage and Offloading (FPSO)) mooring system may contain multiple components: chain stopper, fairlead or bending shoe, chain segments, wire rope, polyester rope, sockets, thimbles, anchors, and connectors or jewelry of various types. Due to its robust nature, chain is usually used at locations along the mooring line that are prone to the highest damage - at the top under high tension and in the touchdown or โthrash zone.โ Two types of chain may be considered for mooring systems: studded and studless. Studded chains have a stud, or brace placed between the bars in the midsection of the chain to prevent flexure and aid in fatigue endurance. Studless chains do not contain a bracing stud. During the design process, an allowance is added to the diameter of chain segments to accommodate for potential material loss due to inservice corrosion and wear. Typically, a design code e.g. API 2SK (API, 2005), or a company specific practice, provides a recommendation or requirement relating an allowed annual corrosion/wear rate. This rate is multiplied by the target design life of the mooring system to reach the total material loss allowance for the mooring chains.
- North America > United States (0.68)
- Europe (0.68)
Abstract This paper describes a methodology for the design and analysis of offshore floating systems governed by squall wind events. A clear methodology on this subject currently does not exist in industry codes and standards. A well-defined methodology is necessary because squalls govern the strength-based design of moored systems in areas such as offshore West Africa. This work focuses on the identification of load cases for time-domain analysis of wind squall events for spread and turret moored vessels. This paper also proposes a method for determining the characteristic design value of extreme line tension and presents various approaches for characterizing extreme vessel offsets. These recommendations are supported and illustrated using results from time-domain analyses of three different offshore systems: two turret-moored ships and one spread-moored ship. This work identifies the conditions that determine maximum offsets and mooring line tensions. These correspond to (1) the relative heading between the vessel and the squall, and (2) the characteristics of the squall. This paper highlights:Modeling details, sensitivity cases, and convergence studies used to establish confidence in characteristic design values that result from the analyses; The number and type of squalls to be considered and identifies topics requiring further research The recommendations in this paper can provide a basis for updates to industry codes and standards related to the design of mooring systems governed by squall events. Prior to the updating of codes and standards, the recommendations included here can be applied to future analyses of moored systems governed by squall events.
Strength Assessment of Degraded Mooring Chains
Crapps, Justin (ExxonMobil Upstream Research Company) | He, Haiping (ExxonMobil Upstream Research Company) | Baker, David (ExxonMobil Upstream Research Company) | Bhattacharjee, Subir (ExxonMobil Production Company) | Majhi, Sai (ExxonMobil Production Company) | Wilutis, Erik (ExxonMobil Development Company)
Abstract This paper presents a framework for strength assessment of degraded mooring chains, based upon laboratory break tests and finite element simulations of degraded chain. Four different modes of degradation, all observed in the field, are considered including: 1) general corrosion, 2) localized corrosion with large single and dual pits, 3) interlink wear, and 4) chain abrasion due to contact with the seabed. For each case, laser scanning was used to obtain the actual geometry of degraded chain taken from the field and the links were then loaded in tension to failure. Material properties were derived from coupon tests of adjacent links to those loaded to failure and the analytic predictions were compared with the actual break loads for each case, validating and demonstrating the robustness of the method. This paper discusses the strength capacity of mooring chains and does not discuss load or demand placed on the mooring system or fatigue endurance of degraded chains. However, mooring system demand will be an integral part of the holistic evaluation of any degraded chains. Case studies detailing the development of strength assessment curves for general corrosion, interlink wear, abrasion, and localized corrosion are presented. A comprehensive investigation covering these four degradation modes is not available to the industry at present. The assessment methodology has a strong technical basis and is expected to provide significant improvements to current industry practice.
- 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)