Volume 41, Issue 3

Imidazoline and imidazoline derivatives are extensively employed as effective corrosion inhibitors due to their low toxicity, low cost and environmental friendliness. Their chemical structure consists of a 5-membered heterocyclic ring (C 3 N 2 H 4 ) with two nitrogen atoms that are readily adsorbed onto metal surfaces. Also, a pendant side chain or alkyl amine substituent acts as an anchor that helps to maintain its adsorption on steel surfaces. The tail portion is a long hydrocarbon chain that can form a hydrophobic film on a surface. These molecular structures make it very attractive as a starting point for several enhancements in corrosion inhibition research. Moreover, modification of an imidazoline structure can be more effective in enhancing its effectiveness in corrosion inhibition. This review compiled all information regarding imidazoline and imidazoline derivatives used as effective corrosion inhibitors in the petroleum industry. It includes their chemical structures and properties, synthesis processes, characterisation and performance evaluations. The review also gives an overview of various types of imidazoline inhibitors with their preparation processes, metal types, corrosive media and concentration range for measurements.

Corrosion under insulation (CUI) is a crucial issue in the industry. Its importance has been increasingly acknowledged because of the high cost and potential danger of causing severe losses. This review gives essential knowledge of CUI and summarizes the research from several aspects, including lab experiments, field tests, CUI prediction methods and numerical simulation research in porous materials. Insulation material, coating, substrate metallic material of the equipment, operating temperature and surroundings are some critical factors that should be considered in the CUI problem. Experimental research methods of CUI and mass transfer in insulation materials were summarized, as well as the applications of data science in CUI prediction. This review also focuses on simulation researches on heat and moisture transfer in porous insulation materials since numerical simulations are helpful for establishing validated models for CUI by modeling to describe the specific processes and predict environmental conditions of CUI for further corrosion research. Combined experimental and simulation work of CUI would be a practical and effective method for CUI research.

Hydrogen transport by blending hydrogen into natural gas transmission pipelines and by pure-hydrogen pipelines is a prospective mode of energy transmission during the transition to renewables. The risk of hydrogen embrittlement (HE) in pipeline steels must first be quantified to ensure safe pipeline operation. This review provides an overview of HE in pipeline steels. Most pipeline steels have reduced ductility when exposed to hydrogen partial pressures of 100 bar and above. Higher-strength pipeline steels (X80 and X100) have been found to undergo HE at ∼50 bar hydrogen. Hydrogen-induced subcritical crack growth in pipeline steels has not been reported in the literature. There are few articles on HE in pipeline welds, with some indications that the weld is more susceptible to HE, and some indications that it is less. The relationship between hydrogen pressure and absorbed hydrogen concentration has not been evaluated. Gaps in knowledge are identified in the conclusions.

Existing natural gas pipelines provide an economic alternative for the transport of hydrogen (H 2 ) in an envisioned hydrogen economy. Hydrogen can dissolve in the steel and cause hydrogen embrittlement (HE), compromising pipeline structural integrity. HE causes subcritical cracking, decreases ductility and fracture toughness, and increases the fatigue crack growth rate (FCGR). This work analyzes the testing standards in gaseous hydrogen used to quantify those effects. Design code ASME B31.12 applicable to hydrogen pipelines has more stringent requirements than ASME B31.8 code commonly used for constructing natural gas pipelines. Differences in materials requirements specified by those codes are summarized. ASME B31.12 pipeline code applies for H 2 at a concentration greater than 10% molar. However, recent testing programs acknowledge that H 2 degrades steel mechanical properties regardless of its percentage in the blend. This paper discusses how the hydrogen degraded mechanical properties affect pipeline integrity. Decreased mechanical properties cause a drop in the failure pressure of a flawed pipeline, calculated following a fitness for service methodology. There is an increasing risk of subcritical crack growth in H 2 as the hardness of base metal and welds increases. This paper analyzes where zones with high hardness and susceptible microstructures are expected in existing pipelines.

Corrosion of metals is considered a global dilemma that is attracting an increasing number of researchers in the scientific community. One of the fundamental solutions against corrosion is using corrosion inhibitors. Corrosion inhibitors are the substances added to the medium or the metal to inhibit corrosion through different mechanisms, most commonly by the formation of a protective layer on the metal surface. Organic corrosion inhibitors constitute most of the known and used corrosion inhibitors, however, due to the toxicity and cost of synthesis, green replacements are needed. Green nanomaterials corrosion inhibitors provide a green and sustainable solution for corrosion. The low toxicity, availability, and cost-effectiveness of green nanoparticles made them a growing research field. This review article highlights the synthesis, use, and application of green nanomaterials in corrosion inhibition. Moreover, the article provides insight into the different types of green nanomaterials inhibitors and their common characterization techniques.

An extensive database of crevice corrosion repassivation potentials ( E R,CREV ) of corrosion-resistant and high-temperature alloys was analysed with statistical tools. Repeatability of results, which considers multiple tests performed by the same team with the same experimental setup, was assessed. Evaluated variables include those that allegedly affect the outcome of testing techniques used to determine E R,CREV such as crevice formers material, applied torque, the extent of corrosion propagation before repassivation and electrochemical procedures; and environmental and metallurgical conditions that may change the corrosion susceptibility of materials such as thermal ageing, alloy composition, temperature, chloride concentration and inhibitors. Guidelines to decide on the significance of changes in crevice corrosion repassivation potentials are proposed. Analysis of collected data suggests that a sample size of 5 is appropriate for assessing any change in the environmental or metallurgical conditions on the repassivation potential.

The effect of zinc (Zn) injection on the stress corrosion cracking (SCC) initiation of an Alloy 182 weld metal and a 20% cold-worked (CW) type 316L stainless steel was investigated under simulated light water reactor conditions. Accelerated SCC initiation tests revealed that under both, boiling (BWR) and pressurized water reactor (PWR) conditions without Zn injection, Alloy 182 showed a higher SCC initiation susceptibility compared to the CW 316L stainless steel. With 40 ppb Zn injection, results indicate a tendency towards higher stress thresholds or lower crack densities for SCC initiation in both materials. In other words, Zn water chemistry seems to be able to mitigate SCC initiation. The optimized, Zn-treated oxide film is believed to be responsible for the improved SCC performance. However, no clear mitigation effects were observed when the specimens were pre-exposed to high-temperature water without Zn and then tested with Zn, which is likely related to the relatively short exposure time to the Zn-containing high-temperature water.