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The current paper deals with a thorough analysis of these newly recognized LHZ with Scanning Electron Microscope (SEM) and Electron Back Scattering Diffraction (EBSD) investigations through the wall thickness of pipes. Internal diameter (ID) surface, intermediate zone and bulk metal microstructures showed an increase of a strong misorientation while approaching the ID. Thus, LHZ is characterized by the presence of lath and especially lower bainite type microstructures associated to high local hardness above the NACE MR 0175 / ISO 15156 limits for sour service applications.
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Corrosion under thermal insulations namely CUI (Corrosion under insulation) is a key degradation process in hydrocarbon facilities which poses asset integrity risks. 1 CUI is reported as the reason behind 40-60% of failures of the process piping in a typical oil refining facility. Speaking smaller-sized process piping (i.e., NPS < 4”), up to 81% of reported failures are known to result from CUI. 2 Monetary spending to inspect and fix CUI-related failures cost 10% of overall maintenance budget in a typical medium-sized oil refinery. 2 CUI risk is influenced by numerous operational and environmental factors which impedes its management in a typical AIM (Asset integrity management) program. The
In natural seawater, microorganisms can fix, grow and develop on practically any surface, including stainless steels, which may cause industrial issues such as microbial induced corrosion, loss of heat transfer efficiency, or undesired colonization from macro-fouling. In particular, the presence of a biofilm on passive alloys such as stainless steels or nickel-based alloys can strongly enhance the cathodic reactions such as reduction of dissolved oxygen, and shift the open-circuit potential (OCP) to the noble direction.This results in an increase in OCP, also called cathodic depolarization or biofilm-induced ennoblement, and affects the risk of localized corrosion, since the critical pitting or crevice potential can be exceeded.
Ammonium Chloride (NH4Cl) corrosion is prevalent in the refinery and petrochemical industries and its prediction, monitoring and control has been well documented. In Chemical plants, when NH3 and HCl are present in a gas-mixture and the temperature drops, NH4Cl can desublime. In the presence of water-vapor, NH4Cl desublime within components like heat-exchanger tubes, creating saturated wet salt deposits, causing general and localized corrosion.
Localized corrosion is known as the most dangerous and unpredictable corrosion mechanisms found in hydrocarbon production and transmission systems. This mode of corrosion has the potential to cause serious financial loss, environmental damage, production interruption, and even loss of life. Over the years, corrosion engineers have made significant improvements on prediction and mitigation techniques to extend the lifespan of carbon steel pipelines, such as using of corrosion inhibitors; injection of such chemicals has proven to be effective and economic, making them a first choice over other alternatives
Corrosion failures in the oil and gas industry are dominated by localized failures in carbon steel; however, the industry has yet to develop standards for localized corrosion specifically for low alloy carbon steels (CS) such as UNS K03014 (API) 5LX65 [X65]) or UNS G10180 (C1018). The reasons for the lack of standardization are understandable as they are not trivial. The challenges are as follows: 1) CS pitting is more complex than pitting on stainless steels (SS) and can be impacted by corrosion byproducts and other forms of scales, and 2) surface finish of a test coupon or electrode has a significant impact on the three phases of pitting: initiation, propagation, and termination.
UNS N06985 is a nickel-based alloy with additions of Mo, Cu and W. Because of its high strength and high resistance to stress corrosion cracking (SCC), cold worked UNS N06985 has been extensively used for OCTG (Oil Country Tubular Goods). The SCC initiation has been studied in Cl-H2S-CO2 containing sour environments; and the SCC resistance was often evaluated using slow strain rate testing (SSRT) for screening by short-term testing and using tensile or C-ring for verification by long-term autoclave testing exposures1. UNS N06985 showed high resistance to SCC at high temperatures in elemental sulfur containing environments with moderate chlorides2.
Nickel-chromium alloys may be susceptible to ordering under certain thermal aging conditions, resulting in the formation of an Ni2Cr phase. The Ni2Cr phase is a superlattice which can result in significant changes of the physical or mechanical properties compared to those of the disordered alloy. Alloy 690, which usually contains a bit less than two nickel atoms per chrom-ium atom, could potentially be susceptible to long-range ordering (LRO) or short-range ordering (SRO). SRO implies that a Cr atom has a high probability of having a Ni nearest neighbor and that small order domains containing at most a few atoms exist. LRO implies that small Ni2Cr clusters exist, and although they may not be visible by transmission electron microscopy (TEM) dark field imaging, they lead to the detection ofadditional diffraction spots in selected area electron diffraction (SAED) patterns, contrary to SRO. Below the critical temperature for LRO, the formation of the long-range ordered structures is preceded by a period of short-range ordering.
Offshore wind farms are important contributions to the growing need for the generation of renewable energy. The number of offshore wind farms is growing, and multiple projects are under planning and construction around the world. One key element for a profitable and sustainable operation of offshore wind farms is that the installations are protected with the most cost-effective corrosion protective solution for the entire lifetime of the offshore wind farm. In practice, this means that today’s projects are planned with an estimated lifetime of a minimum of 35 years without major maintenance of the corrosion protective solution. To achieve this it is instrumental that the entire lifetime cost is considered when a corrosion protective solution is selected.