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Abstract The stress corrosion characteristics of uniaxial glass fibre reinforced thermosetting resin composites have been examined in Hydrochloric acid at room temperature and 80 T. A simple technique based on linear elastic fracture mechanics (LEFM) is presented for characterizing crack growth in these materials subjected to hostile acidic environments. The environmental stress corrosion cracking is investigated both for different types of resin and different types of glass fibre reinforcements Two matrices were used: Bis-A epoxy vinyl ester resin (based on Bisphenol-A epoxy resin) and novolac epoxy vinyl ester resin (based on epoxidised novolac resin) Two glass fibre types were employed: standard E-glass fibre and “R”, a special type of E-glass with superior acid resistance. Model experiments using a modified double cantilever beam test with static loading have been carried out on unidirectional composite specimens in 1M Hydrochloric acid solution at room temperature and 80 °C. The rate of crack growth in the specimen depends on the applied stress, the temperature and the environment Consequently, the lifetime of a component or structure made from GRP, subjected to stress corrosion conditions, could be predicted provided the dependence of crack growth rate on stress intensity at the crack tip is known. Scanning electron microscopy studies of the specimen fracture surfaces have identified the characteristic failure mechanisms. The most important findings of this work is that the selection of epoxy vinyl ester resins reinforced with “R” fibre exhibited superior resistance to crack growth at 80°C compared to similar E-glass reinforced composites at room temperatures INTRODUCTION Few construction materials can safely be used in prolonged contact with aggressive chemicals, especially at elevated temperatures, without corroding, swelling, cracking or dissolving. FRP generally perform well in this respect and materials selection has been made easier. It is not true that FRP materials are inert to chemicals, but they tend to perform well against dilute acids and alkalis and certain other, more harmful chemicals which pose severe problems for steel, brass, zinc and aluminum. Glass fibre reinforced composites (GRP) materials are finding ever increasing applications in various engineering fields e.g. as construction materials in chemical and pollution control plant. These materials provide good mechanical and economical properties, as well as improved resistance to corrosion in hostile environments. The phenomenon of acidic stress corrosion of GRP has been of interest both because of its obvious technological importance and also because of the unique mechanisms of crack growth that are involved. In contrast to metallic corrosion where electrochemical corrosion mechanisms are dominant, a variety of mechanisms playa role in degradation of GRP structures Attack may occur by physical or chemical means or by a combination of both. Chemical attack or corrosion is basically a destruction or deterioration of a material caused by reaction with its environment'' Physical corrosion is a deterioration of resin properties without breaking chemical bonds. In this case, fluid from the environment may diffuse into the plastic causing change (reduction usually) in performance.
- Europe (0.68)
- North America > United States (0.46)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Well Completion > Hydraulic Fracturing (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)
ABSTRACT This paper summarizes a part of a more comprehensive study on DCB test. The effect of specimen thickness on KISSC was evaluated. The results obtained using two different thicknesses are shown. Some considerations about the possible causes of the observed differences in KISSC values are presented. Besides, a method that allows to measure the crack growth in the DCB specimen is described. An ultrasonic technique was used for monitoring the crack extension. INTRODUCTION The presence of H2S in well fluids, that could lead to Sulfide Stress Cracking (SSC) of Oil Country Tubular Goods (OCTG), exerts restrictions on the selection of the materials for OCTG. Increasing development of deep sour wells requires high strength low alloy steels (HSLA steels) with good SSC resistance. Besides, it is well known that when the yield strength of the HSLA steel increases the SSC resistance decreases. The selection is determined by both mechanical properties and the SSC susceptibility of the material. Knowledge of the behavior of steels in presence of H2S is obtained from service experience and laboratory testing. Several test methods, such as those recommended by NACE International, have been used to characterize the SSC susceptibility of a material. For quantitative evaluation NACE TM0177-901 suggests method D, a crack arrest type of fracture mechanics test. This method, that can be traced back in the work of Heady, uses the double cantilever beam (DCB) specimen. The material resistance is measured in terms of a critical value of the stress intensity factor, KISSC.In spite of the test''s acceptability, there are some questions still not clear concerning the specimen thickness influence on KISSC. The crack propagation rate in the specimen could give information to the research point of view. This parameter is not determined by any standard test; for this reason, the development of a method to evaluate crack propagation rate was one of our objectives. In this paper, which summarizes a part of a more comprehensive study on DCB test3,4,5, the effect of specimen thickness on DCB results was evaluated. Besides, a method based on a ultrasonic technique that allows to measure the crack growth during a DCB test is presented. 1-THE EFFECT OF THE SPECIMEN THICKNESS The NACE TM0177-90 sets a value of 9.5 mm (0.375 in) as standard thickness for the DCB specimen. When the thickness of the material being tested is inadequate to meet this requirement, specimens of 6.4 mm (O.25 in) or 4.8 mm (0.15S in) may be used. The KISSC is calculated by using the Heady’s equation for all specimen thicknesses. No plain-strain requirements are included In the standard. Some authors have found out that the KISSC values obtained by using DCB specimens are affected by the specimen thickness. In the Proposed Revision to NACE standard TM0177-90 this fact is pointed out. This part of the paper summarizes the results obtained using two different DCB thicknesses. MATERIALS AND EXPERIMENTAL PROCEDURE Materials Five HSLA steels from commercial heats were used in the tests.
ABSTRACT Because of the local hardening, welded joints in ferritic steels are susceptible to hydrogen-induced stress corrosion cracking. The problem is severe in H2S media, and hardness limits are normally imposed to avoid failure, exemplified by the NACE MR0175 criteria. Such limits have been derived from field experience and laboratory tests under static loading. In practice, most plant undergoes load fluctuation, and the present study examined the effect of a small fluctuating load component on sulphide stress cracking (SSC) behaviour. Weld metals were produced in C–Mn steel using the submerged arc and shielded metal arc processes, to give deposit hardness from 180HV to 245HV. Precracked samples were tested in the NACE TM-0l-77 Method A environment, both statically and with load variations of 5% or 10% of the nominal value, at frequencies of 0.15 and 0.015Hz. Imposition of fluctuating load was found to promote SSC at 245HV, the threshold stress intensity was reduced by up to 60%.The effect of cyclic load was slightly increased at higher load variation and with reduced frequency of application. INTRODUCTION The presence of H2S in a ferritic steel system, such as oil and gas transmission lines, introduces the potential problem of hydrogen-assisted stress corrosion cracking (SCC). Dissolved H2S in aqueous solutions “poisons” the hydrogen atom combination reaction on the steel surface: this encourages the hydrogen to diffuse into the steel rather than allowing recombination to occur, with gaseous hydrogen evolution. Once within the steel, the hydrogen can embrittle the material, and, if a tensile stress is applied, the embrittlement may be sufficient to initiate “sulphide stress cracking” (SSC). The embrittling effect of hydrogen in ferritic steels is more marked in high hardness microstructures, and hence a hardness criterion is commonly stipulated to avoid cracking in “sour” H2S media. For example, NACE standard MR0175–96 recommends a maximum hardness of 22HRC for carbon and allied steels. The NACE MR0175 standard was derived from field studies and laboratory trials using conventional SSC test procedures involving mainly constant load or displacement methods. However, under real service conditions, loading is seldom truly static, and there is considerable evidence from other alloy/environment systems that a small cyclic component (10% maximum load or less) imposed on a structure can have a significant effect on the threshold stress (or stress intensity) to cause failure by a stress corrosion mechanism. The influence. of small-amplitude cyclic loading on SCC in alloys was reviewed by Crooker and Hauser in 1986. This survey covered a wide range of alloys and environments and clearly illustrated the concern that thresholds developed under static loading may be unconservative. However, only one of the papers in this review described work which was carried out on steel under environmental conditions likely to cause hydrogen–assisted SCC.In this work, the threshold stress intensity factor (KISCC) for a 5NiCrMoV steel in 3.5%NaCl solution was reduced by around 40% for 10% cyclic load (ie, a minimum: maximum stress ratio, R, of 0.9), but no effect was observed for AISI 4340 steel.
Abstract A sour burst test of a pressure vessel k described and the results given. The vessel was inspected for existing defects, material properties tested, integrity analyzed and artificial defects introduced before the vessel was subjected to a worst-case environment causing hydrogen charging. The vessel had existing hydrogen-induced cracking (I+IC) and some vertical weld defects. Laboratory materials testing in the hydrogen-charging environment showed the vessel was susceptible to HIC damage, showed no yield strength reduction, reduced plastic ductility in rising load but exhibited brittleness under high plastic strain. No existing or artificial defect initiated the final burst, Sulfide stress cracking (SSC) initiated at a weld produced with temper-bead capping passes but no post weld heat treatment. The vessel survived to 1.2 times actual yield or more than four times its license pressure but the vessel did exhibit a decrease in plastic ductility. Monitoring during the burst test showed that the vessel had been significantly charged with hydrogen. INTRODUCTION To show the conservatism of existing engineering critical assessment (ECA) methodologies in predicting failure of a damaged pressure vessel under wet sour gas conditions; and To validate, if possible, the accuracy of inspection and monitoring techniques for pressure vessels; and To promote the acceptance of ECA for service-damaged pressure vessels in process plant equipment by the various code and regulatory bodies in Canada. The burst test described here is a continuation of a program to validate the methodologies used to predict burst pressure of damaged vessels in various types of service. The initial phase or Phase 1 featured the hydrostatic burst of a damaged vessel under sweet Conditions. The second phase, entitled “ECA of a Hydrogen-Charged Service Damaged Vessel”, features the hydrostatic burst of a damage pressure vessel under wet sour gas conditions. The objectives of Phase 2 are as follows:Phase 2 is sponsored by Canada Centre for Mineral and Energy Technology (CANMET), Shell International Oil Products, Amoco Corporation, Powertech Laboratories, Mobil Oil Canada, Petro-Canada, Syncrude and Suncor/Sun Oil. CANMET managed the program and the Centre for Engineering Research (CFER) conducted the burst. The results of the hydrostatic burst test carried out in Phase 1 showed that the test vessel failed at about 5 times the design pressure in spite of the presence of extensive imperfections. The fracture mechanics analyses, both simple and complex, gave a conservative prediction of burst pressure, A factor of safety of at least 1.5 on the predictions was achieved. The manual ultrasonic testing (UT) tended to conservatively overestimate flaw sizes. The automated methods with pulse-echo techniques gave an improvement in estimating flaw sizes, being less conservative. The automated time of flight diffraction (TOFD) technique was identified as providing the closest estimate of actual flaw sizes. At the time of writing, Phase 2 is not complete. The burst test was executed and post-burst activities begun, Significant results are available and are discussed below. PROJECT STEPS Phase 2 was organized and executed in a similar manner to Phase 1.