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Examines accelerated methods for the corrosion testing of materials, coatings and surface treatments used in the aerospace and defence industries. The drawbacks with some current accelerated corrosion tests are examined, particularly the problems experienced with neutral salt spray tests. Specific examples are given which identify the acute discrepancy between salt spray and marine exposure in the corrosion testing of metallic coatings on steels. Examines some recent advances in corrosion testing of aerospace materials, pre‐treatments and organic coatings, and outlines some preliminary research conducted at DERA Farnborough in developing more accurate test methods.

The purpose of this study was to investigate the influence of doping ions Mg²⁺, Zn²⁺, Al³⁺ to the structure of hydroxyapatite (HAP; Ca₁₀(PO₄)₆(OH)₂) and subsequently to evaluate their adaptation in structure and their anticorrosive properties.

The substituted hydroxyapatite was synthesized by precipitation method that included the addition of Mg²+, Zn²⁺ and Al³⁺ containing precursors to partially replace Ca²⁺ ions in the hydroxyapatite structure. For precipitation synthesis, three ratios of Ca/P = 1; 1.67; 3 and two values of pH = 7 and 12 were selected. Samples 1 (Ca/P = 1; pH = 7), 2 (Ca/P = 1.67; pH = 7), 3 (Ca/P = 3; pH = 7) and 5 (Ca/P = 1.67; pH = 12) were chosen to monitor the influence of doping ions Mg²⁺, Zn²⁺ and Al³⁺ to the structure of hydroxyapatite and its anticorrosive properties.

The chosen synthesis conditions are appropriate for the formation of crystalline HAP substituted by elements Mg, Zn and Al. Only for one sample (1-Mg), two different phases (hydroxyapatite and whitlockite) were identified in the phase composition. On the basis of preliminary corrosion tests, pigments were divided into three groups pursuant to their anticorrosion effectivity: pigments with high corrosion-inhibition efficiency; pigments without anticorrosive properties; and pigments that promote corrosion processes.

In addition, no doping effect can be observed except for the sample 1-Mg, which consists of two phases (hydroxyapatite and whitlockite). Preliminary corrosion tests prove that some samples of HAP have extremely high anticorrosive effectivity as effectivity of the commercial pigments. The accelerated corrosion test showed that HAP samples have insufficient corrosion-inhibition properties for coating applications compared with the commercial pigment.

RESINS AT 1,000°C. A DEVELOPMENT in the field of stable, high‐temperature resins was recently announced by Dr. George Ader of Artrite Resins Ltd., Camberley, Surrey. This was the discovery of resins able to withstand 1,000°C. and more without loss of strength. As the most immediate applications of the material are likely to be in space flight and defence, such as in the manufacture of nose cones and other parts of rockets and missiles, all details connected with this research are secret.

During offshore pipe-lay, pipe lengths with anticorrosion coating are welded together, and, to facilitate the welding process, the ends of the pipe remain uncoated. A wide range of field joint coating (FJC) types is available for coating this bare section, functioning in conjunction with the pipeline cathodic protection system to provide an anti-corrosion system or package. This paper aims to relate to two-layer type heat shrink sleeves (2LHSS), which commonly are used for FJC of concrete-weighted offshore pipelines where the sleeve typically is over-coated with a solid or foam type polyurethane “infill”. Similar sleeves also are used sometimes in exposed conditions on lines without concrete over-coating. The maximum allowable soluble salt contamination prior to application of high-performance coating systems can vary, depending upon the coating type, but typically has been set at 20 mg/m2 (de la Fuente et al., 2006). The first layer of three-layer heat shrink sleeve (3LHSS) systems for pipeline FJC, liquid epoxy, falls into this category (ISO_21809-3:2008, 2008). In contrast, the 2LHSS system does not use a liquid epoxy first layer but relies instead on the bonding of a “mastic” layer directly to the pipe metal surface. The maximum acceptable concentration of salt contamination on prepared metal surfaces prior to the application of 2LHSS has been a subject of debate and was the focus of this study. International standards for FJC do not provide a maximum salt level. However, some companies have continued to specify low thresholds for the maximum allowable salt level for 2LHSS, which can result in expensive delays in production during offshore pipe-lay. In this study, salt contamination levels of up to 120 mg/m2 were found to have no effect on peeling performance after accelerated aging by hot water immersion. Furthermore, preparation for welding and the use of potable water during ultrasonic testing procedures prior to FJC, typically reduces the salt contamination level to below 50 mg/m2 providing a strong case for the deletion of salt contamination testing for 2LHSS.

The potential risk of failure of the coating due to poor surface cleanliness/contamination was assessed by testing the adhesion between the coating and the steel substrate to which the coating is adhering, following a period of hot water immersion. Compliance with ISO 21809-3 “Annex I” requires 28 days’ immersion at maximum operating temperature. For this study, to create a severe situation, the test rings were subjected to accelerated aging by water immersion at the HSS upper specified temperature of 65°C for more than twice the specified period (ISO_21809-3:2008, 2008). Two HSS were tested; one was widely used in applications where exposure to moderate mechanical stress is required, having a high shear strength type mastic “hybrid” adhesive containing a significant proportion of amorphous polypropylene blended with tackifiers and ethylene vinyl acetate (EVA), Andrenacci et al. (2009) referred to as “Type A”. The second, referred to as “Type B”, is widely used in applications where it is covered by a layer of “infill”, typically consisting of polyurethane foam or solid polyurethane elastomer, i.e. typical design methodology for concrete coated pipelines. “Type B” HSS had a more moderate strength traditional type mastic than “Type A” containing a significant percentage of butyl rubber with asphalt, activation agents and tackifying resins. To determine how to apply the salt contamination without causing flash rust, a mini-study was completed on the steel substrate. After numerous trials, it was found impossible to not to form visible rust on the pipe surface. The extent of rusting was minimised by heating the pipe immediately after the application of the salt solution.

High levels of sea salt on power tool prepared pipe surfaces were investigated by peel testing of 2LHSS after hot water immersion and compared against peel tests undertaken prior to hot water immersion. The test conditions were considered severe: salt contamination levels of up to 120 mg/m2 applied on power tool cleaned pipe surfaces that had been aged for one year without prior grit blasting. The accelerated ageing procedure had twice the specified (ISO_21809-3:2008, 2008) water immersion duration, and the test samples had exposed edges providing the possibility for moisture to creep under the coating. The test results showed that there were no noticeable deleterious effects on the performance of the two most commonly used FJCs, 2LHSS. Therefore, it was concluded that, as the level of salt contamination on prepared pipe surfaces after wet non-destructive testing typically is much lower than the levels tested in this study, pipe surfaces prepared for the application of 2LHSS type do not require specific additional measures to further reduce salt contamination, provided that care is taken to ensure that these conditions are maintained consistently during pipe laying operations.

The frequency of salt contamination testing of power tool cleaned surfaces prior to mastic type heat shrink sleeves can be minimised, and perhaps omitted entirely, provided the above criteria are satisfied.

A literature review revealed there was little published information on the testing of 2LHSS and nothing related to hot water immersion testing. Hence, the results of this investigation have provided useful industrial data regarding the effect of hot water ageing and the influence of surface salt contamination on field joint corrosion prevention capabilities.

Probably because the atmospheric corrosion of metals is always associated with the presence of water, the idea of using water‐borne coatings to give protection against corrosion has still not achieved general acceptance. Despite the considerable quantities of aqueous solution primers used in car body dip tanks, there remains a fairly deep‐rooted suspicion of aqueous primers. This may be due to the fact that with all other anti‐corrosive coatings the metal surface must be clean and dry, while aqueous systems inevitably wet the surface.

Broadside Attack. Generally accepted corrosion theories, testing and anti‐corrosion practices had their backs to the wall last month under attack from Dr. J. B. Harrison of Goodlass Wall at the Oil and Colour Chemists' Association meeting in London. Most heavily under fire was the current accelerated corrosion salt‐spray testing practice. No wonder, says Dr. Harrison, there is such widespread discrepancy between results from accelerated tests and the actual long‐term corrosion results. The devil, apparently, is ammonium sulphate contamination, and ammonium sulphate has no place in existing accelerated testing. The accelerated testing conducted by Dr. Harrison in the light of the new theories had both borne out the theories and proved the need for different tests.

Introduction The ever increasing demands made on materials by advanced technology has led, in recent years, to a greater awareness of the importance of mechano‐chemical behaviour. These may be defined as the synergistic effect of mechanical forces and chemical reactions on the material. Although possibly interrelated, three classes of mechano‐chemical reactions have been identified as; stress‐corrosion (SCC), corrosion fatigue (CF) and hydrogen embrittlement. SCC has become one of the ‘in’ subjects of corrosion science during the last decade, while the importance of CF has emerged comparatively recently. In a review of the national corrosion and protection scene in 1970, it was revealed that 62 postgraduate research workers, representing 21% of the total effort in the corrosion and protection field, were involved in mechano‐chemical corrosion studies1. The bulk of these were working on SCC. This large research effort has not resulted in a standardisation of test methods nor, despite several attempts, in a unifying theory for SCC2. The newcomer to the field is faced with a bewildering variety of tests of varying complexity and validity. The supporters of each type of test tend to make exaggerated claims particularly when the test they are advocating is the only one which has caused a particular alloy‐environment system to exhibit SCC.

U.S.S.R. Effect of pH value on iron corrosion. The solubility of iron in media of sufficiently high acidity proceeds mainly through hydrogen depolarisation and without formation of compounds soluble only with difficulty; and the role of pH should be determined chiefly through its effect on hydrogen separation. In work on the nature of the pH effect on corrosion of iron in the presence of inhibitors, tests were made with both pure hydrochloric acid (HCl) and also in the presence of additives: anthranilic acid and tetrabutyl‐ammonium sulphate (TAS). The corrosion rate was determined as usual by loss in weight and expressed in units of current density (amp./sq. cm.). Preliminary tests showed that only in weak solutions (pH 0.61 and 1.06) containing TAS was any divergence noticeable—in connection with the increased role of oxygen depolarisation — between results of quantitative and volumetric methods. Therefore in the present case the corrosion rate is calculated from the volume of separated hydrogen. The pH value was measured with a glass electrode and amplifier, and controlled both before and after test. The tests were made in an aero‐thermostat at 20° ±0.5° and each lasted 24 hr.

In the first part of this article in our September issue, DR. SELLEI dealt with the practical side of engine preservative oil evaluation. In this contribution, she discusses the most important papers covering the theoretical considerations. Engine preservative oils, used for the double purpose of preservation and lubrication, are evaluated as rust preventives and also as lubricants. By carrying the accelerated rusting tests, such as the humidity test, beyond specification limits a method was found which shows the merit of the oils tested and rates them according to their potential rust preventive performance. For evaluating the lubricating performance, engine tests are necessary. Preliminary screening with the Underwood machine and the one cylinder Lauson engine is recommended. A brief summary of the theoretical background of corrosion prevention is presented, with reference to correlation between theoretical considerations and humidity protection.

Admixtures are materials that are added to concrete at some stage in its production to give concrete new properties whether in fluid or plastic conditions. The admixtures used in the construction industry are broadly classified into Mineral and Chemical admixtures. In recent years, the use of mineral and chemical admixtures in producing high performance concrete has increased significantly. The chemical reaction of cement with admixtures differs from material to material. Calcium nitrite based corrosion inhibiting admixtures have gained popularity for protection of reinforced and pre‐stressed concrete structures but calcium nitrite is not commercialized indigenously in India due to manufacturing difficulties. Hence, the objective of the present investigation was to study a novel corrosion inhibiting admixture system and to compare its effectiveness with sodium nitrite.

Di‐sodium phthalate, sodium orthophosphate and sodium nitrite‐based corrosion inhibiting admixtures were selected for the present investigation. The critical quantities of corrosion inhibiting additives were determined by accelerated laboratory tests. The following types of tests were conducted to evaluate the efficiency of the corrosion inhibiting admixtures: compressive strength of 100 × 100 × 100 mm concrete cubes after 3,7,14 and 28 days of curing, linear polarization resistance measurements, electrochemical impedance spectroscopy measurements, an accelerated 12 V controlled potential test.

From the above tests, the inhibitor admixtured concrete not only improved in compressive strength but also increased its corrosion resistance properties. Of the inhibitors studied, di‐sodium phthalate showed superior corrosion resistance properties, compared to sodium nitrite.

Di‐sodium phthalate may be considered a better substitute for calcium nitrite‐based corrosion inhibiting admixtures for durable concrete structures. This fulfils the objective of the investigation.