Eurocorr 2006: ‘Reliability Management of Technical Systems’ – Part 1

By Mills, Douglas J

Over 600 delegates attended the latest Eurocorr event, held on 25- 28 September In the MECC Congress Centre, Maastricht, The Netherlands. The meeting, which proved another success, followed the usual Eurocorr format of parallel oral sessions over three and a half days, and a poster session. The overall organiser on behalf of the EFC (European Federation of Corrosion) was the Netherlands Corrosion Centre (NCQ, with Professor Hans De Wit taking the main responsibility.

Some 275 papers were presented and over 50 countries were represented. Seventeen of the EFC working parties ran sessions and additionally there were joint sessions on: Inhibition/Oil and Gas; Marine/Oil and Gas/CP; Inhibition/Refineries; Coatings/CP; and Steel in Concrete/CP. Special workshops were organised by NCC on Asset Management Control including Support Management and the Aesthetics of Corrosion, and there was also a a NACE meeting.

At the opening ceremony, after a welcome by Jean Jacobs, Deputy Mayor of Maastrichtin, and an introduction to the conference by Hans De Wit, the Cavallaro medal was awarded to Professor George Thompson of the University of Manchester. He gave a very incisive talk entitled ‘New insights into the growth of porous anodic films on aluminium alloys’. Stressing the importance of porous anodic films in providing wear resistance, corrosion resistance, hardness and good appearance, he described the work of his group in understanding the growth of these films. This includes the flow model, in which the anodic oxide flows under stress in the presence of an electric field, leading to expansion of the anodic oxide relative to the oxidised metal.

Professor Thompson showed how tungsten tracers could be used to follow the anodising process in electrolytes such as sulphuric and phosphoric acid. These points were illustrated with excellent ultramicrotome TEM pictures. Although the paper is available on the proceedings CD, he has indicated his willingness to provide it electronically to anyone interested.

George Thompson delivering his Cavallaro Medal lecture

The Kurt Schwabe prize, awarded every three years to an outstanding researcher under the age of 35, was given to Tomas Prosek from the French Corrosion Institute near Paris. He gave a talk on ‘Atmospheric corrosion of carbon steel and zinc in presence of different chloride deposits’ – specifically the effect of cations, showing how for zinc, more chloride forms in the presence of magnesium than forms with calcium than forms with sodium. The order is reversed for steel and this was explained by calcium, and particularly magnesium, suppressing carbonate formation on zinc. One interesting snippet was that Kurt Schwabe had supervised over 300 PhD students!

The third plenary lecture, by Ir. Jacko Aerts from DSM, Corporate in the Netherlands, was on ‘Reliability management of technical systems at DSM’ . This was an interesting talk showing how importantly corrosion is viewed by the management of a processing facility. DSM has a materials and corrosion specialist as part of its multidisciplinary team. One slide specifically detailed corrosion failures!

The conference was generally well organised but there were a couple of weak points. The papers on the conference CD are not uniformly PDF files (most of the papers are in Word). Nonetheless, there is a very good variety among the 295 papers and posters on the CD and many of them are of a high standard. Once again, the poster session seemed to be very much the poor relation (posters were up and down very quickly!) and it would be nice to see greater emphasis on this next year.

Four of the technical sessions at Eurocorr 2006 will be reviewed below and the remainder covered in subsequent issues of CESI

Coatings

Lorenzo Fedrizzi, the Chairman of WP14, ran this session, once again the largest at EuroCorr with 28 papers presented over three days along with 12 posters. There was also a joint coatings and CP session, the two papers in which have been combined into the present review. Of these 40 or so papers, about 35 appeared on the CD and some dozen have been selected for comment below. A number of these chime with the reviewer’s research interest in organic coatings; however, important papers in other areas are also included!

Tomas Prosek

MECC Congress Centre, Maastricht

Mechanical properties of protective coatings are not investigated very often, hence the paper by Berend Boelen from Corus Research, Umuiden, The Netherlands on ‘Influence of deformation on the adhesion of polymer coated packaging steel’ was of interest. The authors claimed that deformation processes reduce significantly the initial very strong coating adhesion and showed how not only is the magnitude of the deformation important but also the steps leading to it. This is reflected in the adhesion, which is markedly better under the witness mark (DRD process) than above, despite the fact that the deformation is changing gradually in this area. Dr Boelen was also involved with another paper, delivered by Arjan MoI from the Technical University of Delft in The Netherlands, ‘Corrosion performance of PETG-coated packaging steel after uniaxial deformation’. PETG (glycol modified amorphous polyethylene terephthalate) coated low carbon steel and ECCS (electrolytic chromium coated steel) were studied using SEM and electrochemical impedance spectroscopy (EIS) in 3-5%NaCI solution at room temperature. The specimens were elongated by 5, 10, 15, 20 and 25%. After deformation to 25% strain the corrosion resistance of the PETG coated ECCS was found to be better than that of the PETG coated steel. Deformation appears to affect the corrosion resistance of the PETG coated steel adversely in a linear fashion.

Several papers looked at electrochemical testing. In ‘Complementary use of EIS and ENM for qualification of organic coatings’ by Tom Bos from TNO, Delft, four industrial coatings were examined in the lab using EIS and the electrochemical noise method (ENM). Also the coating on a ballast tank of a submarine was looked at in situ using a new ENM set-up discussed in a paper at EuroCorr last year (the NOCS method). The R^sub n^ and R^sub p^ values of the industrial coatings and of the coating of the ballast tank were found to be related. Transformation into the frequency domain enabled a direct comparison between Rsn and the modulus of impedance of both electrodes. The NOCS set-up appeared to be successful in the field.

In similar vein was the paper by Douglas Mills from University of Northampton, UK entitled ‘Continuing work to enable electrochemical methods to be used to monitor the performance of organic coatings in the field’. ENM’s advantages (non-intrusive, quickness in gathering data, etc., ease of interpretation) are offset in field work because two separate working electrodes are required. It was shown how either of two novel ENM experimental arrangements, viz. single substrate(SS) or no connection to the substrate (NOCS), overcomes this problem. Also described were methods of dealing with other practical considerations, e.g. dismountable non-marking cells, temporary ‘connectors’ to the substrate and light, battery operated equipment. There was also a need to know the time necessary to leave the specimen in contact with solution before measurement; it was found that for most coatings a time of about 30 min is required. Valrie Sauvant-Moynot from Institut Franais du Ptrole Vernaison (France) dealt with very thick (millimetres) coatings in her paper ‘Use of EIS for the monitoring and modelling of multi-layer anticorrosion coatings’. The durability and anticorrosion properties of three-layer polyolefin coatings exposed to water at 60C (maximum service temperature) were examined. EIS was used to characterise the water uptake and hence the long term barrier properties of coatings on industrial tubes. Gravimetric measurements were also performed during aging on FBE primer coated panels cut from industrially coated tubes to determine the water uptake kinetics using classical destructive techniques. It was shown that the combination of these techniques could effectively predict lifetimes. The intriguingly titled ‘Smart coatings as a key to upgraded life time performance’ was delivered by Amir Eliezer of Sami Shamoon College of Engineering, Beer-Sheva, Israel. This reviewer’s understanding of a smart coating, i.e. one that makes itself more effective at any point of weakness or damage, was not discussed at all; instead, the paper described and gave some results for a new kind of anodising system, ‘the electrochemical high-voltage asymmetric-impulse anodising system’, which creates microplasma coatings.

Maastricht Town Hall

Better in terms of title relating to content was ‘Corrosion protection of heat exchangers using organic coatings’ by Francesco Andreatta from University of Udine, Italy. The barrier properties of E-coating using epoxy resin and of sprayed polyurethane with addition of metallic pigments were evaluated using EIS in 3.5% NaCl solution for different times of immersion. The electrochemical behaviour of coated heat exchangerswas affected by the existence of defects in the coatings. It was observed that E-coatings had difficulty in providing uniform thickness at the fin extremities whereas polyurethane required particular care to fully cover zones with difficult accessibility. More rapid decay of the properties was observed for the polyurethane after long immersion times.

‘Corrosion resistance of thermal sprayed aluminium coatings, in chloride medium’ given by Dayanne Outra de Menezes, Lucio Sathler Federal University of Rio de Janeiro, Brazil reported corrosion resistance of arc sprayed and flame sprayed aluminium coatings in total immersion tests in 3% NaCl solution and natural sea water, at 80C, by electrode potential measurements and surface observation. Samples were unsealed or sealed with epoxy resin or silicone. All coatings protected the steel substrate satisfactorily but there was more attack in 3% NaCl solution.

Several papers discussed pre-treatments for organic coatings. In The effect of thin PANI film on the corrosion behaviour of PANI/ epoxy coated mild steel in acid and neutral solution’ by V.B.MiSkovic-Stankovic at the University of Belgrade, Serbia, 1.5 PANI film on mild steel was electrochemically deposited from aqueous solution of 0.5M sodium benzoate plus 0.1M aniline at constant current density of 1.5 mA cm^sup -2^ and overcoated with a 30 M epoxy layer. The PANI/epoxy coating system exhibited increased corrosion protection after prolonged exposure in 0.1M H^sub 2^SO^sub 4^ and in 0-5M NaCl compared with epoxy alone. This was attributed to protonisation of the leucoemeraldine PANI form occurring in 0.5 H^sub 2^SO^sub 4^, thereby decreasing the concentration of H+ ions in the bottom of epoxy coating pores. In contrast, in 0-5M NaCl dissolved oxygen oxidised leucoemeraldine PANI, inducing an increase in local corrosion potential and consequently causing periodic doping/ dedoping of the PANI film.

Chromate replacement is an important topic at present, hence ‘Study of protection offered by a thin organic layer to galvanised steel in sodium chloride and sulphate solutions’ by Marjorie Olivier from Facult Polytechnique de Mons, Belgium was of interest. Thin organic coatings, e.g. an acrylic polymer and inorganic compounds (titanium, phosphates, …) of thickness <1 m), were tested in chloride and sulphate aqueous solutions and showed good corrosion resistance during a salt spray aging test (200 h without white rust). Potentiodynamic polarisation measurements and EIS were used to follow the aging of the coating. The results showed that the thin organic layer does not really act as a barrier but nonetheless gives a similar protection to a 'classical' conversion coating. In sodium chloride solution, the inorganic compounds seal the initial porosity and thus the active surface area decreases with immersion time. Fatima Montemor from lnstituto Superior Tcnico, Lisbon, Portugal described 'Corrosion performance of doped silane coatings as pre- treatments for multi substrate application'. EIS and the scanning vibrating electrode technique (SVET) were used to investigate galvanised steel, aluminium alloy 2024-T3 and magnesium alloys AZ31 pretreated with bis-[triethoxysilylpropyll tetrasulfide silane (BTESPT) doped with cerium nitrate. The results showed that the Ce- doped coatings provide higher corrosion protection on all the substrates, relative to the undoped coating. Wim Van Ooij from University of Cincinnati, OH, USA had a similar theme but took it further with his paper 'Novel, one-step, chromate-free coatings containing anticorrosion pigments for metals'. These are based on water-dispersed organic resins and organofunctional silanes and the corrosion protection performance of an epoxy/novolac based system for AA20242-T3, had been evaluated using electrochemical methods and performance tests. All the developed coatings survived 2000 h in ASTM B117 salt spray tests. He claimed that these 'superprimers', assure good adhesion to both the substrate and the overcoat.

Finally, the one paper in the combined session on CP and organic coatings was ‘Cathodic protection of organically coated pipelines – scaling-up from lab tests to the field’, delivered by Paul Bailes, from Northumbria University, Newcastle upon Tyne.UK, with the reviewer as co-author. Laboratory tests have been conducted using coated ductile iron pipe and wrapped steel pipe under CP using magnesium anodes and using impressed current. The effect of a break in a coating had been investigated in both 3%NaCl solution and a conducting soil. The current required to establish protection under laboratory conditions has been established for various areas of defect. The values obtained will then be used to scale up the experiments to a medium scale investigation with 3 m lengths of pipe.

Physicochemical techniques

The session run by WP8 on Physicochemical Methods of Corrosion Testing (WP8) comprised 16 oral presentations and 8 posters. The Chairman of this WP is Hans De Wit. Eight of the papers have been selected for comment here, all of which appear on the CD. An interesting new technique was discussed by Afrooz Barnoush from Saarland University Saarbruecken, Germany, in a paper entitled ‘Probing hydrogen embrittlement by in situ electrochemical nanoindentation’. The effect of hydrogen on the nucleation and multiplication of dislocations was examined on precisely oriented Ni(111) surfaces by investigating how changes in the electrochemical potential affected the indent load-displacement curve. The experiments allowed differentiation of surface from hydrogen effects. Results showed that not only the surface films but also the local plasticity is influenced strongly by the potential. Clear evidence was provided that hydrogen atoms facilitate homogenous dislocation nucleation.

Another unusual test was discussed in ‘Advances in assessing the susceptibility to intergranular corrosion (IGC) of duplex stainless steels using the electrochemical reactivation test (ERT)’ by Anke Hempsch, Aachen University of Technology, Germany. The ERT, well established for non-destructive IGC testing of austenitic stainless steels, was shown also to be applicable to duplex stainless steels. The ratio between a time related reactivation current density i^sub R^ and a time related activation current density i^sub A^, normalised to the actual grain boundary area, allowed quantification of the degree of sensitisation. For acceptance criteria in quality assurance systems, a threshold value can be defined. The test protocol has been developed for application both in a laboratory test cell and as a mobile test unit.

‘Pitting liability testing and the risk of technical failures’ was discussed by Ivan Esih, Croatian Society for Materials Protection, Zagreb. Technical failures caused by pitting manifest themselves mostly as perforations of thin-walled structures (pipes, vessels and other hollow objects) or as cracks and fractures at the bottom of pits on structures under stress. Pitting liability is usually estimated on the basis of tests concerning the behaviour of specimens exposed to a particular electrolyte. Pitting is assessed by the number of pits n^sub p^, their depths h^sub p^ and size (orifice areas S^sub p^). For the evaluation of pitting failure risk, important quantities are: maximum pit depth h^sub max^ and number of pits per unit area n^sub p^/S. A greater value of h^sub max^ corresponds to shorter time before the first failure. Increase of n^sub p^/S indicates the probability of more frequent subsequent failures. Based on this, the reliability of failure forecasts was discussed.

Assessing an unusual form of copper corrosion was discussed by Pehkonen Antero, Helsinki University of Technology, Espoo, Finland, in ‘Formicary corrosion of copper alloys’. This type of corrosion is commonly found in heating and cooling coils. In one aspect it appears as longitudinal pits that form interconnecting microscopic tunnels, and this has been termed ‘ant’s nest corrosion’. To discover if formic acid always causes this effect, tests in 0.05 and 5% CHOOCH were carried out. No ‘ant nest’ morphology damage was found, the appearance of the corrosion failures being typical of local pits. Thus, the conclusion was that ‘ant nest’ corrosion failures are a special case of formicary corrosion, the dominant form being typical local or pitting corrosion.

Electrochemical noise is an increasingly useful technique and its application to screen inhibitors was discussed by Peter Plagemann from IFAM Bremen, Germany in his paper ‘Electrochemical current noise measurements for corrosion screening purposes’. The total amount of noise charges was analysed to look at inhibitor effects on aluminium alloy 2024 using an eight-cell multi-channel zero resistance ammeter. Noise charge was calculated and compared with results of measurements made with complementary methods, mostly polarisation curves. Good agreement was obtained. Results of measurements on coated samples with artificial defects were also discussed.

In ‘A novel approach to determination of threshold for stress corrosion cracking (K^sub ISCC^)’ by Raman Singh Raman from Monash University, Melbourne, Australia, circumferential notch tensile (CNT) mild steel specimens were used to generate K^sub Iscc^ data, at the free corrosion potential E^sub corr^, in 12-5M NaOH at 150C; K^sub Iscc^ was determined to be 27-7 MPa m^sup 1/2^. To establish the applicability of the CNT technique to mechanistic analysis of caustic cracking, tests were also performed under imposed electrochemical potentials. When the test was performed at a controlled potential in the active-passive transition region, the specimen failed extremely quickly relative to specimens tested at E^sub corr^, employing similar K^sub I^. Experimental CNT testing was shown to be a simple, relatively fast and cost-effective approach to generating K^sub Iscc^ data. ‘Copper com\position influence on pitting and intergranular corrosion of model AIMgSi (Cu) alloys’ was given by Hetian Zhan from the Netherlands Institute for Metals Research (NIMR), Delft; the work was done in conjunction with Vrije Universiteit Brussel, Belgium. To achieve higher strength, 6xxx alloys often contain copper and hence become susceptible to pitting and intergranular corrosion (IGC). Alloys with 0.03, 0-15 and 0.80%Cu were subjected to the IGC test (ASTM G110). It was found that the average surface density of pitting/IGC sites increased with Cu content, indicating that the lower the Cu content the better the resistance to localised corrosion. FE-SEM- EDX and FE-Auger measurements suggest that the Cu is concentrated in a small area and at a depth of just a few nanometres.

There were also a couple of posters of interest. Adrian Hozoi et al, from TNO Science and Industry, Delft, The Netherlands presented ‘Corrosion monitoring by a wireless sensor network and ultrasonic measurements for pipe corrosion monitoring’. A measurement concept based on the transmission of ultrasonic waves using transducer arrays was developed to allow the coverage of relatively large pipe sections with a limited number of sensors. A wireless sensor network (WSN) controls the ultrasonic measurements, pre-processes the data and routes this information to a central monitoring station (CMS) where tomographic reconstruction to calculate a wall thickness profile can be performed. Corrosion on the brazed joints in absorption refrigeration systems is an important problem. ‘Galvanic corrosion of copper-brassbrazed joints in aqueous lithium bromide solutions from A. ValeroGomez, Universidad Politcnica de Valencia, Spain studied the galvanic effect on joints using electrochemical measurements in 400, 700, 850 g L^sup -1^ LiBr with 4.3 g L^sup -1^ lithium chromate (Li^sub 2^CrO^sub 4^) as inhibitor at 25C. Copper and brass were brazed with a 74.75Cu-7.25P-18Ag ternary filler metal. Corrosion resistance was estimated from the polarisation curves, comparing the values of the open circuit potential, calculating the corrosion potentials and corrosion current densities from Tafel analysis, and establishing the critical potential for each individual material. The inhibitive influence of chromate was analysed. Corrosion galvanic resistance was estimated applying the mixed potential theory. The same techniques will be used to assess non-chromate containing formulations.

Tribocorrosion

Dieter Landholt is the Chair of WP18, which is relatively new. It was good to see a programme of 13 papers and three posters, half a dozen of which have been selected for comment. The first paper to catch this reviewer’s eye related to fretting corrosion work he was involved with at Trent Polytechnic some 20 years previously! ‘Competition between tribo-oxidational and abrasive wear during sliding’ delivered by Abdenacer Berradja from Katholieke Universiteit Leuven, Belgium, investigated depassivationrepassivation behaviour in the corrosion-wear system. Electrochemical open-circuit potential and potentiodynamic polarisation measurements were performed on 304L stainless steel discs sliding against a corundum counterbody in Ringer’s solution. A mechanism involving mechanical depassivation during sliding and subsequent electrochemical repassivation during the latency time between successive contact events was found in both unidirectional and bidirectional sliding. The wear mechanism identified seemed to be a competition between tribo-oxidational and abrasive wear Relevant to coatings for offshore wind turbines was ‘Abrasive effect of beach and desert sands on an organic coating system’, delivered by Flavio Deflorian from University of Trento, Italy. Using electrochemical tests and a modified Taber test apparatus, the effect of different natural sands chosen in function of the dimension of the particles, their morphology and chemical composition on organic coatings had been investigated. The aggressiveness of the sand was found to increase with the grain dimensions and with reduction of the content of calcite in the sand. Desert sands, which had rounded grains, led to a progressive reduction of the protective properties, and were less abrasive than sands having grains with sharp edges. On the other hand, the more abrasive sands tended to create non-uniform tracks with larger defects.

A paper relevant to the important area of corrosion and health was ‘Studies on tribo-corrosion explain low nickel release from Euro coins’ by Lisbeth Hubert from the Technical University of Denmark, Lyngby. Patch tests of euro1 and euro2 coins on the skin has shown eczematous reactions. Nickel release is facilitated by corrosion of the coinage metal and as such is influenced by humidity, temperature and sweat composition. Furthermore it is known that combined corrosion and wear can be synergistic effect, accelerating degradation. Results from electrochemical and tribocorrosion tests surprisingly showed a decrease in anodic current when combining corrosion and wear. A possible explanation for this finding is a change in transport kinetics and the formation of a passivating layer of atacamite (CuCl^sub 2^.SCu(OH)^sub 2^) and malachite (CuCO^sub 3^.Cu(OH)^sub 2^) smeared over the surface by the mechanical rubbing with washable leather during the wear test. ‘Comparative corrosion-wear behaviour of cast iron and aluminium’ was delivered by Amaya lgartua from Centra Technolgico Teknicker, Eibar, Spain. Open circuit potential, electrochemical impedance spectroscopy, and linear sweep voltammetry measurements were carried out on aluminium and cast iron mechanised discs made from a pump wheel in 0-5M H^sub 2^SO^sub 4^, 3-5 %NaCl, and 10% NaCIO. Tribocorrosion tests were performed on pump wheel discs disposed in a ‘ball on disc’ configuration and immersed in 3,5 %NaCl solution (pH 6.1). All the tests were carried out at room temperature under aerated conditions. The lowest corrosion rate was obtained for the aluminium disc immersed in NaCI. Cast iron dissolved quicker than aluminium in acid but showed better behaviour in alkaline solutions, where a thin protective layer of iron hydroxide formed on the disc surface. After friction testing, the corrosion rate increases and the surface state does not recover its initial properties on either material.

1 Changes in antioxidant concentration and carbonyl index for polyolefin pipes (after Brll). This figure has been reproduced with permission from Robert Brll

Finally there was an interesting poster, The study of wear- corrosion resistance properties of ultra-thin diamond-like carbon (DLC) nitride films’, by C. K. Lee from Ching Yun University in Jung- Li, Taiwan. Ion beam assisted deposited films of thickness 1.5, 2.0, 2.5 and 3.0 nm were investigated by electrochemical and weight loss techniques in 1M NaCl+ 1M H^sub 2^SO^sub 4^ solution. The results showed that all the nitrogen containing DLC films provided corrosion protection to the 5088 Al-Mg alloy substrate (with an electroless Ni- P interlayer), and the degree of protection increased with film thickness. Further, the wear-corrosion resistance of all the nitrogen containing DLC films was found to increase with increasing film thickness.

Corrosion of polymer materials

Corrosion of Polymer Materials (WP19) is a relatively new working party (inaugural meeting in Nice in 2004), chaired by Dr Rudolf Morach. All 17 papers from these sessions appear on the CD and about half have been selected for comment.

In Alina Adams Buda’s paper from RWTH Aachen, Germany on ‘Non- destructive testing of PE pipes and welding lines by mobile NMR’, a NMR-MOUSE (nuclear magnetic resonance mobile universal surface explorer) was used to gather morphological data from a section of fresh pipe, deformed according to a pressure test with an external point load, before and after annealing at 8O0C. sections from LDPE coatings of steel pipes that had been in use for 20-30 years were also investigated. With these pipes it was found that the elongation at break rose dramatically after annealing, which assists healing of point deformation. The results raised questions about the validity of the accepted lifetime prediction protocols based on tests at elevated temperatures.

Testing plastics for their susceptibility to environmental stress cracking’ by Thomas Arndt, Rohm GmbH, Darmstadt, Germany, provided an overview of ESC test methods, classified by particular characteristics: number of stages, type of mechanical loading, crack development phase investigated, technique for crack detection, and standardisation of test method. These characteristics were explained using actual examples from a manufacturer of moulding compounds and semi-finished parts made of PMMA and other plastics; the influence of molecular weight and impact modification on the ESC behaviour of PMMA was marked. The examples also shed light on the difficulties and limitations of the methods. The actual test methods were well covered by A. S. Maxwell, National Physical Laboratory, Teddington, UK, in his paper ‘Review of ESC testing and accelerated test methods’. There was a good paper by Michael Rudschuck from DKI Darmstadt, Germany on ‘Testing the sensitivity of plastics parts to environmental crazing for quality assurance and failure analysis’. He said that 30% of all failures are due to environmental crazing initiated by the combination of inner stress and chemicals as lubricants, solvents, etc. It is essential to have a versatile testing fluid which can form crazes in most common plastics types. Current fluids are highly inflammable, volatile and toxic. Hence a test fluid which is non toxic, less volatile and can be applied to polymers such as PC, PS, ABS, SB, PMMA, PSU, PES had been developed. Applications presented demonstrated the capabilities of the new fluid.

An interesting scientific paper was ‘Innovative methods to monitor the media-inf\luence on polyolefins’ by Robert Brll from Deutsches Kunststoff-Institut, Darmstadt, Germany. The life expectancy of pipes was determined by measuring their burst behaviour at a range of pressures and temperatures. The variation of antioxidant concentration and the carbonyl index through the pipe thickness was found to exert an important influence (carbonyl index is an indication of damage of the polyolefin by oxygen) (Fig. 1). The classic approach is sequential analysis of samples following mechanical abrasion of successive layers from the aged pipe, which is labour-intensive and the reproducibility of the abrasion cannot be guaranteed. In this work infrared imaging and X-ray microscopy were successfully used to characterise a PP-R pipe, which had been in use for 10 years.

Hartmut F. Schroeder, BAM, Berlin, Germany discussed ‘A new method for testing the resistance to oxidation application and evaluation: polyolefinic products’. He described an oxidation test in an autoclave, in which acceleration of degradation is realised by elevated oxygen pressure and the specimens are tested immersed in an aqueous medium. The advantage over the standard oven test is lower testing temperatures and the capability of extraction by various liquids (different pH, etc.). A useful general paper was given by Karin Jacobson, from KIMAB, Stockholm, Sweden on Techniques for creating relevant corrosion and diffusion data for polymeric materials’. The author claimed there is a lack of relevant corrosion and diffusion data available for polymeric materials and set out to describe some of the techniques available. Depth of penetration had been measured on cross-sections of plastic materials exposed to corrosive environments, enabling both corrosion and diffusion rates to be calculated. Sometimes the results have to be ‘developed’ by using staining techniques and a number of specific analytical measuring techniques were described. ‘Degradation of recycled polyethylene’ from A. S. Maxwell, National Physical Laboratory, Teddington, UK, was relevant in the context of end of life issues. Sections from two identical HDPE mouldings, one exposed to natural weathering for several years, the other kept in a controlled indoor environment, were examined. Material removed from these mouldings was reprocessed and moulded. Specimens were then subjected to accelerated weathering in a xenon arc chamber. Characterisation revealed that although the properties of each batch were similar immediately after reprocessing, those subjected to outdoor exposure before reprocessing degraded more rapidly. Finally, ‘Qualification of composite material lined downhole tubing for gas production’ by Kevin Waterton from CAPCIS Ltd, UK, reported work done in conjunction with Statoil ASA, Norway. A test programme had been performed to verify the suitability of glass fibre reinforced epoxy composite lined tubing for use in a typical Middle East gas production situation. Material coupons were exposed in Hastelloy autoclaves to three phases: brine, liquid hydrocarbon and a gas mixture (methane, H^sub 2^S, CO2) at 320 bar pressure for up to 2000 h at 110, 130 and 150C. The mechanical properties determined were used to estimate temperature limits, which were clearly above the service temperature of 110C. The results obtained from the test programme indicate that the GRE liner material will retain adequate properties for a 25 year service life.

Copyright Institute of Materials Mar 2007

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