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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.
Ngonyoza, Ntsikelelo (Oman Oil Refineries and Petroleum Industries Company (ORPIC)) | Al Hamdi, Abdulaziz (Oman Oil Refineries and Petroleum Industries Company (ORPIC)) | Al Balushi, Aliaa (Oman Oil Refineries and Petroleum Industries Company (ORPIC)) | Blakey, Robin (Oman Oil Refineries and Petroleum Industries Company (ORPIC))
This paper explores the various degradation mechanisms experienced by a refinery’s RFCC catalyst cooler aeration piping system. A detailed analysis of the most recent failure and a past failure was conducted to determine the various metallurgical and mechanical degradation mechanism(s) that led to these failures. The analysis which covered both the old UNS S30409, TP304H stainless steel, and newly upgraded UNS S34709, TP347H stainless steel catalyst cooler aeration piping system, with the same design, showed the dominant degradation mechanisms to be low cycle thermal fatigue and low cycle fatigue- creep for the TP304H and TP347H stainless steel aeration system’s header and sub header. The TP304H aeration system failed after three years in-service and the TP347H aeration system after six months in-service. The proposed solutions to prevent recurrence include a design change of the aeration piping system, stricter quality control during fabrication, installation of liquid knock-out drums to prevent water ingress resulting in thermo-mechanical strains and a return to the TP304H metallurgy for the aeration system pending a detailed investigation into the TP347H failure.
The paper also explores the technical reason(s) for the metallurgy upgrade from TP304H to TP347H and how this change affected the aeration piping’s service life.
A refinery’s Residue Fluid Catalytic Cracking Unit (RFCC) experienced repeated failures of its Regenerator Catalyst Coolers’ aeration piping system. The RFCC Catalyst Coolers are external vertical shell-and-tube type heat exchangers. In the present unit, two Catalyst Coolers, 1 and 2, are located on either side of the Regenerator. The purpose of the catalyst coolers is to reduce the temperature of the regenerated catalyst by generating of steam from the circulating boiler feed water on the tube side of the exchanger. During operation, regenerated catalyst flows over the entire cross sectional area of the tube bundle. The aeration system provides uniform air distribution on the shell side of the catalyst cooler exchangers thereby fluidizing the catalyst to allow for better catalyst flow and a uniform heat transfer coefficient. A catalyst cooler failure results in a forced refinery stoppage/shut-down for repairs. The primary location failure is at the weld joints of the aeration piping system due to various stresses and strains acting on the aeration system. The catalyst cooler failures follow a general sequence of events, as described below: