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ABSTRACT Literature information concerning the effect of liquid hydrocarbons on flow-induced sweet (FIS) corrosion is limited and most of the currently available prediction models exclude the roles of liquid hydrocarbons in FIS corrosion. Results of an innovative test method, employing a rotating cylinder electrode tester and liquid hydrocarbon-brine two-phase fluids, successfully isolated the roles of hydrocarbons in FIS corrosion. It was found that the concurrent presence of liquid hydrocarbon and water phases, which were flowing but distinctively separated, promoted localized (interfacial) corrosion at the hydrocarbon/brine interface. Evidently formation of passive carbonate films was severely hampered at the liquid hydrocarbon/water interface. When both phases were in either a quiescent condition or severely mixed, however, the interfacial corrosion did not occur. The severity of the interfacial corrosion was sensitive to rotating speed, temperature, and liquid hydrocarbon type. Influencing the chemi-sorption crystallization process of protective iron carbonate films, the liquid hydrocarbon phase appears to destabilize the formation of passive iron carbonate films on a carbon steel surface under FIS corrosion environments. INTRODUCTION For the last two decades, flow-induced sweet (FIS) corrosion has been investigated from many different aspects and thus well documented. The mechanistic understanding on FIS corrosion of carbon steel has been considerably improved. Various governing factors such as temperature, flow characteristics, brine chemistry, partial pressure of carbon dioxide, pre-surface condition, etc. have been evaluated and successfully studied by lab or field corrosion engineers. Many prediction models have been then developed to predict the aggressiveness of FIS corrosion as a function of temperature, partial pressure of CO2, pH of the solution etc. Some of them include wall shear stress as well. They are effectively utilized in the industry. It is not uncommon, however, to observe discrepancies between actual and predicted corrosion rates. One of the fundamental reasons widening the discrepancy seems to be related to the limited understanding in the roles of liquid hydrocarbons (hereafter hydrocarbons) in FIS corrosion. 1-6 All in all, handling hydrocarbons is in fact cumbersome in a lab because hydrocarbons are not conducive with maintaining experimental cleanliness. As a result, most of the lab experiments as well as many prediction models exclude hydrocarbons. Even when included, as described below, hydrocarbons are generally considered only as a partitioning agent of corrosion inhibitors and many simply consider hydrocarbons as an insulating entity in the sweet corrosion reactions. This work intended to uncover and isolate the roles of hydrocarbons which would be a stepping stone to have a complete grasp on FIS corrosion. ROLES OF HYDROCARBONS IN LITERATURE One of the most intriguing phenomena in FIS corrosion is its localized form of attack to carbon steel. A CO2 containing fluid tends to form an iron carbonate film which has varying degrees of protectiveness depending upon various controlling parameters such as temperature, partial pressure of CO2, flow rate, etc. Localized FIS corrosion occurs when one or more of the following four conditions are met: · ? The presence of uneven flow (mainly washing effect) · Forming an iron carbonate film with varying degrees of protectiveness · ? The presence of uneven ferrous ion saturation rate · ? The presence of hydrocarbons It is not difficult to envision that uneven flow on a pipe surface could promote localized corrosion regardless of fluid character
- North America > United States (1.00)
- Asia > Middle East > Israel > Mediterranean Sea (0.24)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
- Facilities Design, Construction and Operation > Natural Gas Conversion and Storage > Liquified natural gas (LNG) (1.00)
ABSTRACT Insulation panels are fitted to the inner hull of LNG carriers by bonding with a load bearing epoxy mastic adhesive onto the inner steel surface of the double hull. The steel surfaces of the hull are usually protected after blast cleaning with a wash primer. The adhesion strength between the steel surface and the primer will depend on various conditions; a number of factors will affect the adhesion such as steel surface preparation, the film thickness and types of primer used. In this study we evaluated the adhesion strength and their corrosion properties at different film thickness for each of the primers used, and also the method of surface preparation used for the steel substrate. In addition we evaluated the temporary anti-corrosion properties of primers by carrying out comparative tests, which has been used for a similar purpose in the past. Adhesion strength of both primers to surfaces prepared by power tool grinding shows superior adhesion than that of blast cleaning, this is due to power tool grinding providing a more efficient anchor pattern. In case of where the coating thickness is lower than the physical roughness of steel surface, the corrosion resistance of the specimens prepared by power tool grinding is higher than those prepared by blast cleaning. Also, the microstructure and hardness of steel substrate influences the formation of the anchor pattern. Therefore, the hardness Of the steel substrate should be considered when selecting the most appropriate method of surface preparation. In case of DFT less than 75~m wash primer shows better corrosion resistance than epoxy Zn primer. However, at higher DFT epoxy Zn primer shows considerably increase in corrosion resistance. INTRODUCTION LNG(Liquefied Natural Gas) is transported at -163°C under atmospheric pressure. LNG tanks form an integrated part of the construction of the vessel and are contained within the double hull of the vessel, and will therefore be subject to a significant temperature gradient:-163°C on one side (LNG cryogenic temperature conditions) and at ambient temperature: + 20~40°C on the other side (double-hull steel plating). To maintain stability of the LNG the area surrounding the cargo tank is insulated with composite: plywood/R-PUF foam/plywood (reinforced rigid closed cell foam boards). Insulation panels are bonded to the inner hull of LNG carriers by epoxy mastic adhesive in the shape of rope as shown in Figure 1. The main element is to provide sustained long term adhesion for the weight loading of the insulation panel, relies on the adhesion of the epoxy mastic. The main purpose of wash primer in LNG carriers is primarily to protect the steel or metal surfaces. Basic vinyl butyral wash coat is sometimes referred to as wash primer. It contains carefully balanced proportions of an inhibiting chromate pigment, phosphoric acid, and a synthetic resin binder mixed in an alcohol solvent. It gives excellent adhesion, partly to chemical reaction with the substrate, and at the same time, forms a corrosion-inhibiting vinyl film that contains inhibitive pigment to help prevent rusting. Therefore, wash primer is applied for temporary corrosion protection of the steel substrate for between 3 to 6 months. The adhesion and bond strength of the wash primer could affect the adhesion between the insulation panel and the inner hull. This means the adhesion and bond strength of the primer can be correlated with the type of surface preparation method used for the steel substrate, and film thickness. In the case of thick coating films, the coating itself can fail due to a decrease in the cohesive strength as the film thickness increases. Following installation the insulation panel, nitrogen
- Transportation > Freight & Logistics Services > Shipping > Tanker (1.00)
- Energy > Oil & Gas > Midstream (1.00)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
- Facilities Design, Construction and Operation > Natural Gas Conversion and Storage > Liquified natural gas (LNG) (1.00)