|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
Clad pipes are manufactured both with and without a thin nickel interlayer. Diffusion of carbon from the base material to the clad, which degrades the structure adjacent to the interface and increases the local embrittlement, is effectively reduced by this interlayer. However, a majority of the existing subsea clad pipes are without this interlayer, and diffusion of carbon at the bimetallic interface is an issue that still needs to be addressed. This paper presents a methodology for calculation of carbon diffusion, or any other elements, that accounts for the combined heat exposure in the production process of the clad pipes and in an eventual repair welding. In the welding simulation the local temperatures are logged and the resulting file is modified afterwards to include data, if available, from the diffusion bonding process. In the diffusion calculation temperatures are not calculated but read from this log file. Identical thermal history in the welding simulation and subsequent diffusion simulation is therefore ensured with diffusion coefficients being dependent on the temperature and on the type of microstructure. A case study, that concludes that the diffusion bonding process is the major contributor to diffusion of carbon, demonstrates the methodology.
Utilization of clad and lined pipes, where a thin layer of corrosion resistant alloy (CRA) provides corrosion resistance inside a conventional carbon steel pipe, is with increasing frequency considered as an economically viable alternative for corrosion management in many new oil and gas developments. Different production techniques are used to manufacture these pipes. While lined pipes are manufactured by mechanical expansion of a CRA pipe to the backing pipe, production of clad pipes is by metallurgical bonding of the clad to the backing material.
Microstructure and mechanical properties of such pipes are influenced by the method these are manufactured. Temperature, pressure and time are key parameters which influence on the diffusion of the atomic species. Diffusion of major alloying elements in steels like carbon that migrates from the base metal to the clad and chromium diffusion to the grain boundaries, influences on the structure and the ductility of the backing steel at the base-clad interface. Changes in the composition at and adjacent to the bimetallic interface and formation of chromium carbides at the grain boundaries in the clad, resulting in the formation of chromium-depleted zones adjacent to the grain boundaries (sensitization), is a well-known problem that can occur during welding or improper heat treatment.
Mahajanam, Sudhakar (Pinnacle Advanced Reliability Technologies) | Addington, Fred (Pinnacle Advanced Reliability Technologies) | Folse, Joanna (Pinnacle Advanced Reliability Technologies) | Sayegh, Gillian (Pinnacle Advanced Reliability Technologies) | Espinoza, Cesar (Pinnacle Advanced Reliability Technologies) | Cubides, Yenny (Texas A & M University) | Sprinkle, Scott (Hunt Refining Company) | Kornegay, Joseph (Hunt Refining Company) | Vining, Joe (Hunt Refining Company)
Corrosion Resistant Alloys (CRAs) are routinely utilized to mitigate against the complex damage mechanisms encountered in refining operations that carbon and low alloy steels are highly susceptible to. However, CRA materials can suffer similar corrosion damage when improperly manufactured or exposed to aggressive environments. In this paper, three modes of CRA failure observed at a client’s site were analyzed in a lab and mitigation strategies proposed.
Tower trays near the top of a crude tower made of UNS S41008 martensitic stainless steel (SS) failed as a result of localized under-salt corrosion due to formation of amine hydrochloride salts. Appropriate crude pre-treatment was implemented to mitigate this corrosion mechanism.
UNS N06625 flexible hoses located at the inlet of a reformer in a hydrogen plant failed upon start-up during a turnaround. It was found that these materials were heavily sensitized with embrittling phases present at the austenite grain boundaries. Improper annealing processes at the manufacturing plant likely caused the sensitization of the microstructure.
Downstream of the reformers, UNS S30403 austenitic SS tube ends of the boiler feed water heat exchanger underwent a failure. The tube to fixed tube sheet seal weld failed as a result of fatigue cracking originating at a lack of weld deposit location. Ensuring a proper weld profile in compliance with the weld procedure would reduce such stress riser concentrations.
Carbon steel has been the most common structural material used for oil and gas applications since its development around 1870. However, high susceptibility to corrosion has limited the use of carbon steel under aggressive operating conditions.1 Corrosion resistant alloys (CRAs) were developed in the 1980s as alternative materials for the extreme service conditions and corrosive produced fluids typically encountered in the oil and gas industry.1 CRAs generally refer to martensitic stainless steel (SS), duplex SS, austenitic SS, and nickel-based alloys that form a passive film on the metal surface which protects it against corrosive environments.2-4 CRAs were initially designed to prevent CO2 corrosion in pipelines but recent advances have been primarily oriented towards increasing the corrosion resistance of these materials to other corrosion mechanisms such as sulfide stress corrosion (SSC) cracking, chloride stress corrosion cracking (Cl-SCC), and hydrogen embrittlement.1 Common examples of CRAs used for oil and gas applications include austenitic SSs such as UNS S30400 and UNS S31603, martensitic SSs such as UNS S41000, duplex SSs such as UNS S31803 and UNS S32750, super austenitic SSs such as UNS N08904, and Ni-based alloys such as UNS N06625.1 Although these CRAs are expected to provide long-term corrosion resistance in oil and gas environments, they can still suffer from different corrosion issues, depending on metallurgical factors such as chemical composition, heat treatment, microstructure, and strength, and environmental conditions including temperature, chloride concentration, CO2 partial pressure, H2S partial pressure, pH of the solution, and presence of elemental sulfur.4-7 These factors can deteriorate the passive film stability, and increase the susceptibility to pitting corrosion and the likelihood of any form of environmentally assisted cracking. Thus, significant efforts have been made to implement proper material selection procedures, considering mechanical properties and corrosion resistance, to avoid premature failure of CRAs under specific service conditions.4, 6 In this study, failure of three different CRAs (UNS S41008, UNS N06625, UNS S30403) in refining operations will be investigated. A brief description of these materials and corrosion mechanisms associated with their failure are also presented.
Koo, J.Y. (ExxonMobil Research and Engineering Company) | Luton, M.J. (ExxonMobil Research and Engineering Company) | Bangaru, N.V. (ExxonMobil Research and Engineering Company) | Petkovic, R.A. (ExxonMobil Research and Engineering Company) | Fairchild, D.P. (ExxonMobil Upstream Research Company) | Petersen, C.W. (ExxonMobil Upstream Research Company) | Asahi, H. (Nippon Steel Corporation) | Hara, T. (Nippon Steel Corporation) | Terada, Y. (Nippon Steel Corporation) | Sugiyama, M. (Nippon Steel Corporation) | Tamehiro, H. (Nippon Steel Corporation) | Komizo, Y. (Sumitomo Metal Industries Ltd.) | Okaguchi, S. (Sumitomo Metal Industries Ltd.) | Hamada, M. (Sumitomo Metal Industries Ltd.) | Yamamoto, A. (Sumitomo Metal Industries Ltd.) | Takeuchi, I. (Sumitomo Metal Industries Ltd.)
This paper describes the metallurgical science used to develop a new, weldable, high-strength linepipe (X120) for the transport of natural gas. A domain-based microstructure design has been used to ensure ductile fracture behavior at temperatures down to −20°C. Ultra refinement involving careful chemistry design and thermomechanical controlled processing (TMCP) produced fine domains below about 2 μm within prior austenite pancakes below about 6 μm in thickness. To achieve the target properties in the pipe body, seam weld and girth weld heat-affected zones (HAZ), 3 low-carbon microstructure designs have been produced. Low-carbon chemistry and Nb/V micro-alloying combined with boron additions were used to impart sufficient HAZ cold cracking resistance and to limit softening in the seam weld HAZ. Both the lower bainite and the dual-phase microstructures provided superior property combinations. INTRODUCTION Natural gas is an increasingly attractive energy source, but major reserves are often remotely located from potential markets. While high operating pressures and/or thin-wall pipes are a means to reduce gas transmission costs, conventional steels typically lack sufficient strength. To address these challenges, a significant advance in steel-making and plate-manufacturing technology is necessary. This paper describes the metallurgical design basis for X120-grade pipeline steel for low-temperature service, including Arctic environments. Over the past 30 years, the trend toward increased transportation efficiency has largely been achieved by increasing the diameter of pipelines. Currently, large systems that are installed on land consist of 1420-mm–diameter (56-in) pipe operating at pressures in the range between 70 and 100 bar (1015−1450 psi). In such cases, the pipelines are typically constructed from X65or X70 API grades. At the present time, the highest-strength linepipe that has been applied in sufficient quantities to be considered commercial is the X80 grade, which has a yield strength of 560 MPa (80 ksi).
Koo, J.Y. (Corporate Strategic Research, ExxonMobil Research and Engineering Company) | Luton, M.J. (Corporate Strategic Research, ExxonMobil Research and Engineering Company) | Bangaru, N.V. (Corporate Strategic Research, ExxonMobil Research and Engineering Company) | Petkovic, R.A. (Corporate Strategic Research, ExxonMobil Research and Engineering Company) | Fairchild, D.P. (ExxonMobil Upstream Research Company) | Petersen, C.W. (ExxonMobil Upstream Research Company) | Asahi, H. (Technical Development Bureau, Nippon Steel Corporation, Chiba Institute of Technology) | Hara, T. (Technical Development Bureau, Nippon Steel Corporation, Chiba Institute of Technology) | Terada, Y. (Technical Development Bureau, Nippon Steel Corporation, Chiba Institute of Technology) | Sugiyama, M. (Technical Development Bureau, Nippon Steel Corporation, Chiba Institute of Technology) | Tamehiro, H. (Technical Development Bureau, Nippon Steel Corporation, Chiba Institute of Technology) | Komizo, Y. (Corporate Research Laboratories) | Okaguchi, S. (Corporate Research Laboratories) | Hamada, M. (Corporate Research Laboratories) | Yamamoto, A. (Kashima Steel Works) | Takeuchi, I. (Tokyo Head Office, Sumitomo Metal Industries Ltd)