Extensive Corrosion Research Articles

The Influence of $\hbox{H}_{2}\hbox{S}$ Exposure on Immersion-Silver-Finished PCBs Under Mixed-Flow Gas Testing

This study focuses on the corrosion of immersion silver (ImAg)-finished copper land patterns on printed circuit boards (PCBs) under H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S exposure. Eight test conditions were examined with varying levels of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S, temperature, relative humidity, and exposure time. The results indicated both direct chemical-reaction corrosion and electrode-reaction corrosion, particularly galvanic corrosion. H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas was a stronger driving force for corrosion on ImAg-finished PCBs than SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas. Temperature had a significant influence on ImAg-finished surface PCBs. Tests found extensive corrosion on ImAg-finished PCBs at 40°C, even in very low humidity. On ImAg-finished surfaces, the corrosion was nonuniform during the early period of exposure, with the corrosion modes being mainly pitting, open mouth, and particles. The corrosion products at this early stage mainly included Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O and Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S. As time progressed, the corrosion products mainly included Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S, Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S, CuS, and CuO. These formed a passive film on the surface. ImAg-finished PCBs are vulnerable to H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas; nonuniform severe corrosion was found to occur at defects on the ImAg surfaces. The mixed-flow gas test produced creep corrosion on ImAg-finished PCBs using only H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas. Dendrite corrosion products growing from an edge with a solder mask were generally longer than those growing from an edge without a solder mask. The corrosion products of these dendrites mainly included Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S or CuS.

Treasures of Portuguese archaeology Notes towards a preventive conservation project

The permanent exhibition “Treasures of Portuguese Archaeology” of the Portuguese National Archaeological Museum is composed mainly of gold and silver artefacts which present extensive surface corrosion. The construction of the exhibition room dates from the late 1980s, and it was conceived with the highest security standards in mind. However, at that time, the importance of the choice of compatible materials and equipments for the exhibition of metal artefacts was still unknown, and the same was true for the influence in terms of corrosion development, even for gold objects, if an inappropriate material was selected. Preventive conservation directives and actions have been developed since then, and presently one is confronted with new paradigms for the exhibition and preservation of artefacts, and, moreover, of cultural heritage. A preventive conservation project, which is currently in its initial stages, was set up with the objective of identifying and understanding the pathologies observed, in order to correct the problems presented by the exhibition room. This article presents an overall view of the project, a description of the alterations observed, and a summary of the methods proposed for obtaining responses to the respective problems, with the purpose of correcting the room’s fragilities.

Increased wear of aqueous lubricated short carbon fiber reinforced polyetheretherketone (PEEK/SCF) composites due to galvanic fiber corrosion

It was previously reported that under certain conditions an electric current that transgresses the interface of a short carbon fiber (SCF)/polyetheretherketone (PEEK) composite vs. a X10CrNiMoTi1810 steel pairing causes extensive galvanic corrosion of the composite's short carbon fibers [1]. In order to elucidate the influence of this phenomenon on the wear resistance of PEEK/SCF, different PEEK/SCF composites were exposed to unidirectional sliding wear under the same environmental conditions that led to fiber corrosion. Our results indicate that there is a mutual amplification of wear and fiber corrosion. Comparing different fiber types, we found the pitch based carbon fiber investigated is much more susceptible to galvanic corrosion than the polyacrylnitrile (PAN) based one. The pitch based carbon fiber corroded so severely that one of the PEEK/pitch SCF composites exhibited even a higher specific wear rate than neat PEEK.

Corrosion analysis and treatment of two paintings on zinc supports by Frederick Preedy

Two oil paintings on zinc supports by Frederick Preedy were examined, analysed, researched and treated in order to stabilise them and reinstate them to the original locations in the Church of St David in Little Dewchurch, Hereford. The paintings had been moved from display in the early twentieth century due to their condition. They had acquired a thick build‐up of surface dirt. In addition extensive corrosion and deterioration had resulted in structural instability and damage. Before treatment the composition of the paintings and the identity of the corrosion products were examined. With no articles about paintings on zinc apparent in the conservation literature, treatments were guided by information gathered from a variety of sources. It is hoped that this paper will generate discussion and research in the conservation of oil paintings on zinc supports. Résumé «Analyse de la corrosion et traitement de deux peintures sur support de zinc de Frederick Preedy» Deux peintures à l'huile sur support de zinc de Frederick Preedy furent examinées, analysées, étudiées et traitées afin de les stabiliser et les réinstaller sur leur lieu d'origine dans l'église Saint David à Little Dewchurch, Hereford. Les peintures ont été déplacées de leur lieu d'exposition au début du XXè siècle à cause de leur état. Une épaisse couche d'encrassement s'était accumulée sur leur surface. De plus, une corrosion et une détérioration importantes ont provoqué une instabilité structurelle et des altérations. Avant traitement, la composition des peintures et la nature des produits de corrosion furent examinées. Etant donné qu'aucun article sur les peintures sur zinc n'apparaissait dans le domaine de la conservation, les traitements furent guidés par des informations recueillies auprès de diverses sources. Il est à espérer que cet article va susciter une discussion et une recherche sur la conservation des peintures à l'huile sur support de zinc. Zusammenfassung „Analyse von Metallfraß und restauratorische Behandlung von zwei Gemälden auf Zinktafeln von Frederick Preedy” Zwei Ölgemälde auf Zinkplatten von Frederick Preedy wurden untersucht, analysiert, recherchiert und anschließend konservatorisch behandelt, um sie zu stabilisieren und an ihren ursprünglichen Standort seitlich der Retabeln in der Kirche von St David in Little Dewchurch, Herefordshire, zu reinstallieren. Die Gemälde waren im frühen 20. Jahrhundert wegen ihres schlechten Erhaltungszustandes von den Wänden der Kirche abgenommen worden. Sie wiesen eine dicke Schmutzschicht auf. Weitreichender Metallfraß und genereller Verfall hatten zu schweren Schäden an der Substanz und struktureller Instabilität der Gemälde geführt. Vor der Behandlung wurde der Aufbau der Gemälde untersucht, und die Zersetzungsprodukte identifiziert. Da bisher keine Veröffentlichungen über Gemälde auf Zink in der Restaurierungsliteratur bekannt waren, orientierte sich die restauratorische Behandlung an Informationen aus verschiedenen Quellen. Die Autoren hoffen, dass durch diesen Artikel weitere Diskussionen und Untersuchungen zum Thema Ölgemälde auf Zink angeregt werden. Resumen “Análisis de corrosión y tratamiento de dos pinturas con soportes de zinc de Frederick Preedy” Dos pinturas al óleo con soportes de zinc de Frederick Preedy han sido examinadas, analizadas, investigadas y tratadas para estabilizarlas y reinstalarlas en su localización original en la iglesia de St. David en Little Dewchurch, Hereford. Estas pinturas fueron removidas de la exhibición donde se encontraban a principios del siglo XX debido a su condición, ya que habían adquirido una densa capa de suciedad superficial. Además, la extensa corrosión y deterioración había causado inestabilidad estructural y daños a las obras. Antes del tratamiento, se examinaron la composición de las pinturas y la identidad de los productos corrosivos. Como aparentemente no hay artículos referentes a pinturas con soporte de zinc en la literatura de conservación, los tratamientos se dirigieron siguiendo la información recopilada en otras fuentes. Se espera que este artículo genere discusión e investigación en la conservación de pinturas al óleo con soportes de zinc.

Observations and analysis of a 63-year-old reinforced concrete promenade railing exposed to the North Sea

Despite being exposed to the harsh sea-spray environment of the North Sea at Arbroath, Scotland, for over 63 years, many of the reinforced concrete precast beam elements of the 1·5 km long promenade railing are still in very good condition and show little evidence of reinforcement corrosion. In contrast, railing replacements constructed in about 1968 and in 1993 are almost all badly cracked as a result of extensive corrosion of the longitudinal reinforcement. This is despite the newer concrete appearing to be of better quality than the 1943 concrete. Statistics for maximum crack width for each of the three populations, based on measurements made in 2004 and in 2006, are presented. In situ and laboratory measurements show that the 1943 concrete appears to have high permeability but it also shows high electrical resistivity. Chloride penetration measurements show the 1943 and 1993 concretes to have similar chloride profiles and similar chloride concentrations at the reinforcement bars. This is inconsistent with the 1943 beams showing much less reinforcement corrosion than their later replacements and casts doubt on the conventional practice for durability design focusing on reducing concrete permeability through denser concretes or greater cover.

Evaluation of Environmentally Friendly Zr Based Nano Structured Conversion Coating for HRS (Hot Rolled Steel) in Powder Coating

Metals, despite their deterioration in a corrosive atmosphere, continue to dominate the automotive, agricultural, furniture, process and appliance industries and HRS (Hot Rolled Steel) plays a significant role in those areas. Powder coating on HRS is widely employed for protective and aesthetic purposes. Prior to powder coating, phosphating conversion coating is often used to increase effectiveness of protection. However, due to tightening environmental legislations, phosphating process is now problems for industry. Therefore, newly developed environmentally friendly conversion coats are introduced to industry. In this study a new environmentally friendly zirconium fluoro-based (H2ZrF6) generation of conversion coating has been introduced to replace the conventional phosphating conversion coatings process. It is deposited on the surface with a thin nanometre range, therefore shortening the process, which also has advantages such as being free of heavy metal and operating in low or ambient temperature. The present work closely examines Zr based nano structured conversion coatings for HRS. Extensive corrosion and adhesion studies are carried out on differently prepared HRS test panels, pre-treated with Zr based conversion coating in various conditions, such as different composition ratio, temperature and contact time.

Crack -Healing Behaviour of Zirconia/SiC Composite Ceramics

ZrO2/SiC composite ceramics were sintered and subjected to three-point bending. A surface crack of 100μm in diameter was made on each specimen. We studied crack-healing behavior. The main conclusions are as follows. (1) ZrO2/SiC composite ceramics could heal a crack. Then the best healing condition is 800°C × 30h in air. (2) A crack was healed even at 600°C, which was a very low temperature compared with other ceramics. (3) The ZrO2/Y2O3/SiC system ceramics caused an extensive corrosion at over 1000°C. (4) Healing temperature and the minimum -time to heal were in the good proportional relation on the Arrhenius diagram at 600–800°C.

Corrosion of dental nickel–aluminum bronze with a minor gold content‐mechanism and biological impact

To study corrosion and to evaluate biological effects in vitro of corrosion products of a copper-aluminum-nickel alloy with 2% gold. The alloy NPGtrade mark+2 with the nominal composition Cu:77.3; Al:7.8; Ni:4.3; Fe:3.0; Zn:2.7; Au:2.0; and Mn:1.7 was characterized. Static immersion in acidic saline, pH 2.2-2.4, was used to determine release of metallic elements in a milieu simulating the condition of plaque build-up in interproximal areas of the tooth. Corrosion and surface reactions in saline and artificial saliva were studied by electrochemical techniques including registration of open-circuit-potentials, polarization curves and impedance spectra. Extracts were made in cell culture media and acidic saline and used for MTT test for cytotoxicity and HET-CAM method for irritation. The mean amount of elements released in the acidic saline were in microg cm(-2) : Cu:632; Al:210; Ni:144; Fe:122; Zn:48; Mn:52. No protective film was formed on the surface of the alloy, as extensive corrosion was observed in both saline and artificial saliva. The corrosion rate was higher in saline than in artificial saliva. Acidic extracts of the alloy diluted up to 64 times reduced cell viability with 80% or more. The extract induced coagulation of the blood vessels of the CAM and was rated as moderate irritant solution. The nickel-aluminum bronze showed high corrosion rate caused by an inability to create a protective surface layer. High levels of toxic elements were found after static immersion testing, and the corrosion products had a distinct adverse effect on the biological activity.

Materials corrosion in molten LiF–NaF–KF salt

Corrosion tests of high temperature alloys, Hastelloy-N, Hastelloy-X, Haynes-230, Inconel-617, and Incoloy-800H were performed in molten fluoride salt, FLiNaK (LiF–NaF–KF:46.5–11.5–42 mol%) with the goal of understanding the corrosion mechanisms and ranking these alloys for their suitability for molten fluoride salt heat exchanger and thermal storage applications. The tests were performed at 850 °C for 500 h in sealed graphite crucibles under an argon cover gas. Corrosion was noted to occur predominantly by dealloying of Cr from the alloys, an effect that was particularly pronounced at the grain boundaries of these alloys. Weight-loss due to corrosion generally correlated with the initial Cr-content of the alloys, and was consistent with the Cr-content measured in the salts after corrosion tests. Two Cr-free alloys, Ni-201 and Nb–1Zr, were also tested. Ni-201, a nearly pure Ni alloy with minor alloying additions, exhibited good resistance to corrosion, whereas Nb–1Zr alloy exhibited extensive corrosion attack. The graphite crucible may have accelerated the corrosion process by promoting the formation of carbide phases on the walls of the test crucibles, but did not alter the basic corrosion mechanism.

Corrosion Behavior of Type 304 Stainless Steel in a Simulated Seawater-Based Medium in the Presence and Absence of AerobicPseudomonasNCIMB 2021 Bacteria

A comparative study of the corrosion behavior of type 304 stainless steel (304 SS) in a nutrient-rich simulated seawater-based medium in the presence and absence of a marine aerobic Pseudomonas NCIMB 2021 bacterium was carried out. Electrochemical studies (including Tafel plots and electrochemical impedance spectroscopy) revealed that 304 SS underwent different corrosion processes under the attack of Pseudomonas bacteria. In the absence of the Pseudomonas bacterium, the passivating film on 304 SS remained relatively stable, and the anodic reaction was under diffusion control. Colonization of the Pseudomonas biofilm on the coupon surface led to the acceleration of corrosion rates and a dramatic decrease in resistance of passivating film due to localized breakdown of the film. Scanning electron microscopy (SEM) results revealed an increase in heterogeneity and coverage of the biofilms of Pseudomonas bacterium with exposure time. Extensive micropitting corrosion underneath the biofilms was also observed, in ...

Corrosion of superheater steel materials under alkali salt deposits Part 1: The effect of salt deposit composition and temperature

This paper is the first in a series of two reporting on results from an extensive laboratory-scale corrosion study where tailor-made well-characterized synthetic alkali salt deposits were used for corrosion testing of several steel materials used in or aimed for recovery boiler superheater tubing. The corrosion testing was done in temperatures ranging from 450 to 600 °C. The synthetic alkali salt deposits, containing sodium, potassium sulfates and chlorides, were composed in such a way that their first melting temperature, T 0, and the amount of melt formed at this temperature, varied for each salt mixture. The results showed on one hand that an increased amount of melt in the salt deposit increased the corrosion of the steel material markedly. The results showed, however also, that corrosion could take place at temperatures clearly below any melting of the salt deposits if the composition was suitable. This took place with salts that contained chlorine. Already a very low amount of chlorine in the salt caused corrosion at temperatures typical for superheaters in the recovery boiler. These effects are qualitatively well-known from earlier but it was surprising that already a very small amount of chlorine caused significant increase in corrosion. To stress the importance of the deposit layer on the corrosion we introduce two new terms: (1) sub- T 0 corrosion, indicating corrosion taking place below any melting of the deposit and (2) super- T 0 corrosion, indicating corrosion taking place when the deposit contains melt.

Corrosion of electrocast AZS refractories by CAS glass–ceramics melting

Extensive corrosion experiments on electrocast alumina–zirconia–silica (AZS) refractories by molten CaO–Al2O3–SiO2 (CAS) and Na2O–CaO–SiO2 (NCS) glasses were carried out at various temperatures under static condition. The features and mechanism of the corrosion were compared and analyzed. The changes of microstructure and phase composition of refractories in the course of the melt corrosion were also studied. X-ray diffraction (XRD), scanning electron microscope (SEM) and chemical analysis were used to characterize the corroded refractory materials and reacted melts. The reasons of alumina–zirconia–silica bricks corroded are the meltdown of their own composition, penetration or permeation of alkali oxide in the glass melt and scouring of the glass melt. The results show that the refractories resistance against corrosion of the oxides like Na2O, K2O or CaO is weak, and that the corrosion mechanism of NCS/AZS is different from that of CAS/AZS. In a static condition, CaO–Al2O3–SiO2 melts corroded alumina–zirconia–silica brick more severely than Na2O–CaO–SiO2. The result provides useful reference to a prospective selection of refractory materials in glass and glass–ceramics manufacture.

The effect of prior deformation on stress corrosion cracking growth rates of Alloy 600 materials in a simulated pressurized water reactor primary water

The effect of prior deformation on stress corrosion cracking (SCC) growth rates of Alloy 600 materials in a simulated pressurized water reactor primary water environment is studied. The prior deformation was introduced by welding procedure or by cold working. Values of Vickers hardness in the Alloy 600 weld heat-affected zone (HAZ) and in the cold worked (CW) Alloy 600 materials are higher than that in the base metal. The significantly hardened area in the HAZ is within a distance of about 2–3 mm away from the fusion line. Electron backscatter diffraction (EPSD) results show significant amounts of plastic strain in the Alloy 600 HAZ and in the cold worked Alloy 600 materials. Stress corrosion cracking growth rate tests were performed in a simulated pressurized water reactor primary water environment. Extensive intergranular stress corrosion cracking (IGSCC) was found in the Alloy 600 HAZ, 8% and 20% CW Alloy 600 specimens. The crack growth rate in the Alloy 600 HAZ is close to that in the 8% CW base metal, which is significantly lower than that in the 20% CW base metal, but much higher than that in the as-received base metal. Mixed intergranular and transgranular SCC was found in the 40% CW Alloy 600 specimen. The crack growth rate in the 40% CW Alloy 600 was lower than that in the 20% CW Alloy 600. The effect of hardening on crack growth rate can be related to the crack tip mechanics, the sub-microstructure (or subdivision of grain) after cross-rolling, and their interactions with the oxidation kinetics.

Corrosion of Pure Titanium Sternal Wire

Titanium and its alloys are considered reliable materials commonly used in heart surgeries. A patient had severe inflammation at the median sternotomy wound develop after open heart surgery. Sternal wires were removed and were found to be seriously corroded on most of the surface. Energy dispersive spectroscopy identified titanium as the only elemental component of the explanted wire with grade 2 purity, and the polarization curve showed satisfactory corrosion resistance similar to commercial pure titanium. Prolonged inflammation might have caused extensive corrosion of titanium in the present case.

Effect of corrosion on the low cycle fatigue behavior of Sn–4.0Ag–0.5Cu lead-free solder joints

Isothermal low cycle fatigue tests using Sn–4.0Ag–0.5Cu solder joints were performed according to a full factorial design of experiments in different corrosive environments. Temperature, humidity and salt solution were varied according to literature. The application of salt solution resulted in extensive corrosion of the solder joints and a decrease in fatigue life. The factor with the highest effect on the fatigue life was salt solution followed by temperature. The factor humidity was not significant for the present fatigue tests performed. The experiments performed at room temperature at different strain ranges also revealed that the application of salt decreases the fatigue life (90% confidence). The fatigue exponent α increases and C decreases when salt solution (concentration of 1 M) is applied to the solder joints. The two Coffin–Manson plots diverged from each other when decreasing the plastic strain range.

Microbiologically influenced corrosion of 304 stainless steel by aerobic Pseudomonas NCIMB 2021 bacteria: AFM and XPS study

Microbiologically influenced corrosion (MIC) of stainless steel 304 by a marine aerobic Pseudomonas bacterium in a seawater-based medium was investigated by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM was used to observe in situ the proliferation of a sessile Pseudomonas cell by binary fission. The development of a biofilm on the coupon surface and the extent of corrosion damage beneath the biofilm after various exposure times were also characterized by AFM. Results showed that the biofilm formed on the coupon surface increased in thickness and heterogeneity with time, and thus resulting in the occurrence of extensive micro-pitting corrosion; whist the depth of pits increased linearly with time. The XPS results confirmed that the colonization of Pseudomonas bacteria on the coupon surface induced subtle changes in the alloy elemental composition in the outermost layer of surface films. The most significant feature resulting from microbial colonization on the coupon surface was the depletion of iron (Fe) and the enrichment of chromium (Cr) content as compared to a control coupon exposed to the sterile medium, and the enrichment of Cr increased with time. These compositional changes in the main alloying elements may be correlated with the occurrence of extensive micropitting corrosion on the surface.

330 模擬BWR水環境中におけるSUS316L溶接金属の応力腐食割れき裂進展挙動に及ぼす水化学の影響(OS10-1 応力腐食割れ,減肉配管,OS10 エネルギー機器の経年変化に関する健全性評価手法の開発とその適用(1))

The effect of dissolved oxygen (DO) content and the resultant electrochemical potential on the stress corrosion cracking growth rate of 316L weld metals in simulated boiling water reactor environments was investigated by using fracture mechanics specimens and in-situ crack growth monitoring. The fracture surfaces show extensive interdendritic stress corrosion characteristics. The crack growth rate in 2ppm DO water is significantly higher that in 0.2ppm DO water. The effect of higher DO concentrations such as 7.5ppm or 11ppm on crack growth rate are different for 316L weld metals with different ferrite contents.

Mediation of Endoevaporitic Microbial Communities in Early Replacement of Gypsum by Dolomite: A Case Study from Miocene Lake Deposits of the Madrid Basin, Spain

Abstract Based on petrographic, mineralogical, isotope, and facies assemblage analysis, a microbial origin is established for the formation of dolomite associated with gypsum in Miocene evaporite lake deposits of the Madrid Basin, central Spain. In these deposits, dolomite is present as both intercalated carbonate beds, locally showing domal stromatolite structures between packages of selenite Christmas tree-like gypsum, and patches replacing macrocrystalline gypsum. Texture of the dolomite is characterized by crystal aggregates showing a variety of crystal sizes and morphologies, e.g., platelets, rhombs, micro-rods, and rings, whilst larger crystals are commonly spherical and/or wheat-grain shaped. Organic remains, in the form of filaments, shrubs, micro-fibrils, and strands, are also common and contain significant amounts of carbon. These textural features are also recognized in dolomite replacing gypsum, where Fe oxide and sulfide as well as celestite are ubiquitous mixed with the dolomite groundmass. The dolomite, whether primary or replacing gypsum, is poorly ordered and slightly Ca-rich, thus non stoichiometric. Stable-isotope compositions are characterized by negative values for both oxygen and carbon. Dolomite beds featuring domal stromatolites have δ18O values ranging from −2.99‰ and −3.79‰ and δ13C values ranging from −4.67‰ and −7.35‰, whilst δ13C values determined in the dolomite replacive of gypsum shows a small range of variation between −5.70‰ and −6.96‰. By contrast, δ18O values of replacive dolomite oscillate in a wider range (from −3.04‰ to −7.99‰). Formation of the dolomite was associated mainly with microbial mats, having taken place in relatively diluted lake water. Further evaporative concentration resulted in precipitation of gypsum crystals sealing the mats and creating endoevaporitic microenvironments in which endolithic cyanobaterial activity produced extensive boring and corrosion of the gypsum crystals. Hiatuses in gypsum growth caused an intensification of the corrosion process and favored the precipitation of dolomite mediated by microbes, resulting in pervasive replacement of the sulfate.

Stress and Strain Analysis of Pipelines with Localized Metal Loss

This paper presents the analysis of stress and strain data acquired with the finite element method and with tests that used post-yielding strain gages bonded onto the external surface of pipes that suffered thickness metal loss and that had been loaded with internal pressure. These metal loss areas were produced by three different processes: actual internal corrosion, careful machining of external patches by spark-erosion, and milling of internal or external patches to simulate limited or extensive strip corrosion defects with depths up to 70% of the pipe’s thickness. Results show that: (1) the extensive longitudinal internal or external defect areas behave as extensive strips with a high degree of freedom to deform elastically and plastically in the circumferential and thickness directions, and (2) large restraints are offered to the longitudinal strains by the non-corroded thick walls parallel to the strip. Using the above experimental observation, a simple mathematical model was developed to predict the burst pressure of pipes with longitudinal extensive and reasonably constant depths of metal loss. This model employed thin-pipe-strength-of-material equations associated to a bulging correction factor, the material’s uniaxial ultimate strength and the von Mises criterion. The onset of plastic collapse predicted by the simple model was successfully compared with results determined from actual hydrostatic tests that were carried out with full scale pipe specimens and from finite element results generated by the use of a commercial program. The developed model was also helpful in showing that the yield and burst behaviors of new or corroded pipeline specimens under laboratory test conditions can be directly compared and extended to the yield and burst behaviors of buried pipeline in field operation.

DEGRADATION OF CARBON FIBER/EPOXY COMPOSITES BY XE LAMP AND HUMIDITY

In order to understand the effect of natural environmental factors on the carbon fiber/epoxy composites, the degradation of carbon fiber/epoxy composite was studied. The specimens were exposed in a Xe lamp chamber and suffered to ultraviolet light radiation, temperature and/or humidity conditions. The results show that the radiation, temperature and/or humidity could cause extensive corrosion to the surface and interior of the carbon/epoxy composite and attack the interface between matrix and carbon fiber, resulting in an obvious reduction of the transverse tensile strength and interlaminar shear strength. On the contrary, the longitudinal transverse shear strength was not affected much by the radiation, temperature and/or humidity. The results indicate that the radiation, temperature and/or humidity can result in the corrosion of the carbon/epoxy composite and consequently affect the mechanical properties of the carbon/epoxy composite partially.