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The objective of surface preparation is to create proper adhesion of a coating over the substrate. Proper surface preparation is vital to the long life and effectiveness of a coating applied in corrosive service. In some projects, the owners ask for the additional water jet cleaning prior to blasting work.
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Application of inhibitors is an established and cost effective method to mitigate corrosion of mild steel. Conventionally surfactant-type organic inhibitors are frequently applied based on their critical micelle concentration (CMC) values and their adsorption were evaluated based on reduction in corrosion rate. In this work the relationship between CMC and inhibitor adsorption was explored using a quartz crystal microbalance (EQCM); two quaternary ammonium model compounds with different alkyl tail lengths introduced at concentrations above and below their CMC. The quaternary ammonium model compounds were synthesized in-house and characterized by 1H NMR prior to their use. Their CMCs were determined using surface tension measurements. It was found that at concentrations above and below CMC adsorption of the inhibitors is approximately identical and corresponds to their existing as multilayers on the substrate.
Offshore oil production facilities are subject to internal corrosion, potentially leading to human and environmental risk and significant economic losses. Microbiologically influenced corrosion (MIC) and reservoir souring are important factors for corrosion-related maintenance costs in the petroleum industry.1 MIC is caused by sulfate-reducing prokaryotes (SRP), which can be Bacteria (SRB) or Archaea (SRA), with the main focus in literature being on SRB.2–5 The microorganisms most frequently reported in literature to be responsible for MIC are the SRB; Desulfovibrio, Desulfobacter, Desulfomonas, Desulfotomaculum, Desulfobacterium, Desulfobotulus, and Desulfotignum, and methanogens.2,5
The NACE Standard DCB test Method D provides a measure of resistance to crack propagation in sour environment; expressed in terms of a critical intensity factor for Sulfide Stress Cracking. Testing conditions must be such to ensure crack initiation since is a crack arrest type of fracture mechanics test. To ensure crack initiation the formation of a sharp crack tip by fatigue precracking is permitted by the mentioned standard; however the conditions in which precracking procedure must be performed are not so well established and were modified over the years. Definition of pre-cracking load is crucial for obtaining the true value of since excessive load will produce an increment of the plastic zone at the crack tip that will delay crack initiation generating overestimation of that could not be otherwise noticeable. Despite the selection of pre-cracking load and procedure has a clear impact on Method D result criterion of NACE TM0177 has changed over the yearsand nowadays differs in the maximum precracking intensity factor defined for C110 in API 5CT. The main objective of this work is to quantify the effect of pre-cracking load on sour resistance for the High Strength Steel grades tested with different arm displacement. Tests were performed NACE A solution and SR39.3 solution for C110 and in NACE A for the future C125 grade at 24°C.
Alloy 600 is known to be susceptible to intergranular attack (IGA) and stress corrosion cracking (SCC) under pressurized water reactor (PWR) primary water conditions, leading to the replacement of some steam generator components with the more SCC-resistant Alloy 690.3 Despite this shift many Alloy 600 components are still found in service today. A substantial body of research has identified many underlying processes leading to the degradation of Alloy 600.
Wire ropes with a sheathed spiral strand are commonly used for mooring applications in offshore oil and gas production. Each strand comprises a bundle of galvanized steel wires with a blocking compound applied to the outer layer of the wire bundle to prevent seawater from contacting the internal strands of wire if there is a breach in the urethane cover. The blocking compound and a sacrificial zinc layer on each strand of wire are designed to protect the carbon steel.
Depending on the water depth where the wire rope is being used offshore, it can experience a wide range of temperatures—from 22°C at the surface to 4°C at the seabed. Corrosion behavior of wires at these temperatures is critical, in case of breach in the urethane cover.
Immersion and electrochemical corrosion testing was performed on subsea mooring line wire rope with and without blocking compound in synthetic seawater at 4°C, 13°C, and 22°C. Samples of galvanized wire with and without blocking compound at the lowest temperature (4°C) did not exhibit any iron corrosion products even after 160 days of exposure to synthetic seawater. The corrosion rate of galvanized steel with blocking compound remained less than 2 mpy, while that for galvanized steel without blocking compound remained less than 5 mpy.
Calcium ions are usually present at high concentrations in brines produced with oil and gas. Such brines are typically saturated with respect to CaCO3. Consequently precipitation of CaCO3 as scale on the internal wall of the pipeline can readily occur due to changes in operational and environmental parameters when produced fluids are transmitted from downhole to surface facilities. Despite its importance there is minimal research in the literature addressing the effect of calcium ions and specifically CaCO3 scale on the CO2 corrosion mechanism. Moreover the available literature on this topic is contradictory with undefined water chemistry and flow characteristics of the employed experimental setups. This highlights the need for further systematic experimental studies in this frequently ignored area of corrosion research. The main objectives of this work were to further broaden the mechanistic understanding of CO2 corrosion of mild steel (pH from 5.5 to 6.2 with [Ca2+] from 160 to 6000 ppm to simulate CaCO3 saturation) and evaluate the protectiveness of CaCO3 (without the interference of ferrous ions) against further corrosion; a novel experimental methodology was developed and utilized. The corrosion behavior was studied in situ by electrochemical methods including linear polarization resistance (LPR) electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) along with weight loss (WL) methods for a UNS G10180 with ferritic-pearlitic microstructure. Surface characterization of the scale and corrosion product was performed using scanning electron microscopy (SEM) energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) techniques. Unprotective CaCO3 scale was observed to act as a mass transfer barrier that can promote surface conditions favoring FeCO3 precipitation. Contrary to previous reported research the presence of CaCO3 scale did not result in onset of localized corrosion at the conducted experimental conditions.
Steel components in refineries and petrochemical plants are exposed to conditions of temperatures higher than 200°C with high pressures of hydrogen. Such conditions avail the driving force needed for the hydrogen to dissociate and penetrate the steel surface. Once the atomic or nascent hydrogen is within the steel microstructure, it can react with the carbon present, usually in carbides, to form methane gas within the steel structure as suggested by the below reactions:[C]α + 4[H]α → [CH4]gas (1)where α refers to ferrite.
Polythionic Acid Stress Corrosion Cracking (PASCC) of conventional austenitic stainless steel is serious problem at desulfurization units in petroleum refinery.Post Weld Heat Treatment after welding and/or neutralization treatment using alkaline solution are required during each turn around to prevent PASCC according to NACE SP0170-2012.It has been known that proprietary version Type 347LN has superior PASCC resistance even if without Post Weld Heat Treatment (PWHT) compared with Type 347(H) or Type 321(H). Although the proprietary version Type 347LN is lower C content compare with standardized C content range (0.02%) to suppress precipitation of M23C6 carbide it is not reported that the effect of the slight variation of C content to PASCC resistance.Therefore the relationship between C content and PASCC resistance was investigated by using long term aged samples with simulated welding Heat Affected Zone. As the result it was clarified that the strict control of C content less than 0.015% was effective to keep superior PASCC resistance under extra low C content range less than 0.02%.Key words: Polythionic acid stress corrosion cracking Sensitization Proprietary version Type 347LN Hydroprocessing C content matching filler weld metalBest regardsTakahiro Osuki from NSSMC