Long-term behaviour of aramid fibre

PhD ThesisAn investigation of the creep rupture of Kevlar@ 29, Twaron@ 1000, and Technora T2000 aramid fibre yams was carried out in the temperature range 25-120T in air and three other environments (Saudi/Iranian crude oil, pure water, and low pH water) at 65T with the objective of characterising the long term failure behaviour of these fibres and determine if they can be used to replace the stress rupture test conducted on RTP for qualification purposes. The standard loglo-loglo ISO 9080 extrapolation procedure, the modified lin-logio ISO 9080 extrapolation procedure and the time temperature superposition method were used to model and interpret the results. When tested in air, the different yams showed similar but not identical regression parameters. The results of the standard logio-logio ISO 9080 and the modified lin-logio methods correlated well. The standard logio-logio form, however, gave slightly higher values for the 20 year mean stress and LPL. Its use is recommended because it is consistent with the model assumed in the regression of RTP. There was no evidence of any 'knee' in the relationships after long periods or at high temperatures. This suggests that there is no change in failure mechanism, and lends confidence to both the long term use of aramid fibre in air and the recommended qualification procedures. RTP regression curve constants and those of tested aramid fibre were similar indicating the validity of aramid fibre stress rupture tests as a replacement for RTP tests. Crude oil immersion produced a small but significant reduction in behaviour. At 650C a suitable crude oil reduction factor applied to the long ten-n LPL would be 0.9. Pure water produces a marked reduction in strength after short periods, at 65C. Finally, water of low pH resulted in a large reduction in performance and considerable scatter with one fibre type. With the other, the effect appeared to be similar to that of pure water. Based on the understanding of the failure mechanism and the creep process in aramid fibres, a creep strain model is proposed for estimating the strain to failure based on the material's properties.Saudi Aramc

RELIABILITY OF DISSIMILAR METAL WELDS SUBJECTED TO SULFIDE STRESS CRACKING

Serious concerns have been raised in recent years in the Oil & Gas Industry about the reliability of Dissimilar Metal Welds (DMWs) in sour service. The primary reason for these concerns is because DMW joints exhibit small-localized hard zones that are susceptible to Sulfide Stress Cracking (SSC). In the open literature some methods such as preheating have been suggested to overcome the problem of hard zone formation. The objective of this study is to assess the effect of Sulfide Stress Cracking (SSC) on the reliability (mechanical integrity) of DMWs specimens fabricated with different preheat temperatures and electrodes exposed to sour service environment. The National Association of Corrosion Engineers (NACE) Standard Tensile Test TM 01-77-96 Method A was used to determine the influence of SSC on DMWs in a systematic manner. Test results show considerable improvement in the Time-To- Failure as a result of the preheating methods used. However, it does not appear that the hard zones can be reliably eliminated for manual welding methods, even with the nickel-base electrode, and the optimum preheat temperature. Metallographic Examination and Scanning Electron Microscope Characterization were also used to assess the susceptibility and the failure modes

RELIABILITY OF DISSIMILAR METAL WELDS SUBJECTED TO SULFIDE STRESS CRACKING

Serious concerns have been raised in recent years in the Oil & Gas Industry about the reliability of Dissimilar Metal Welds (DMWs) in sour service. The primary reason for these concerns is because DMW joints exhibit small-localized hard zones that are susceptible to Sulfide Stress Cracking (SSC). In the open literature some methods such as preheating have been suggested to overcome the problem of hard zone formation. The objective of this study is to assess the effect of Sulfide Stress Cracking (SSC) on the reliability (mechanical integrity) of DMWs specimens fabricated with different preheat temperatures and electrodes exposed to sour service environment. The National Association of Corrosion Engineers (NACE) Standard Tensile Test TM 01-77-96 Method A was used to determine the influence of SSC on DMWs in a systematic manner. Test results show considerable improvement in the Time-To- Failure as a result of the preheating methods used. However, it does not appear that the hard zones can be reliably eliminated for manual welding methods, even with the nickel-base electrode, and the optimum preheat temperature. Metallographic Examination and Scanning Electron Microscope Characterization were also used to assess the susceptibility and the failure modes