This paper is the first of three describing the monitoring of filament wound cylinders using Bragg grating sensors. Part I describes the technological issues and the development of specimens instrumented with embedded gratings and thermocouples. The aim is to monitor the temperature and strain changes during cylinder manufacture (see Part II) and in-service behaviour (see Part III). Specimens are filament wound glass reinforced epoxy composites, so two technological problems have to be solved: one is to collect data during fabrication and the second is to remove the specimen from the mandrel without damaging the sensors. These were accomplished by design of a specially adapted split mandrel and a rotating interface between the filament winding machine and the composite cylinder in fabrication. Immediately after sensor insertion it was possible to monitor the fabrication process, by collecting Bragg grating wavelength and temperature response, using this specially adapted tooling.
The precipitation characterization of Al-4 mass% Cu-0.3 mass% Mg alloy with additions of 0.5 and 2 mass% Ag during aging treatments was carried out by transmission electron microscopy (TEM) and microhardness measurements. TEM observation of aged samples showed that the phase is the dominant phase and it is in coexistence with the 0 phase. Additionally, the phase has the morphology of polygonal prism (almost hexagonal) with flat interfaces and a thin thickness. The variation of the cube of mean radius of precipitates, r 3 , followed a linear relationship, as predicted by the Lifshitz, Slyosov and Wagner (LSW) theory for diffusion-controlled coarsening in both alloys. The coarsening process of the phase was slower in the aged Al-4 mass% Cu-0.3 mass% Mg-2 mass% Ag alloy. The decrease in hardness seems to be related to the coarsening of the phase and the loss of coherency.
This paper presents the results of experimental and in-service observations of the nucleation and growth of hydrogen-induced cracking (HIC) in hydrocarbon transport pipelines made of type API 5L steel. The experimental work was done by inducing HIC on steel plates by electrochemical cathodic hydrogen charging and using a straight beam ultrasonic inspection technique to observe the crack growth behavior. Scanning electron microscopy was also used to observe the crack nucleation and propagation mechanisms. The study was complemented by the fractographic analysis of a pipe segment removed from a sour gas pipeline after an in-service rupture caused by HIC, so the pipe segment contained a significant group of blisters and laminations caused by HIC. The results of the cathodic charging indicated that HIC cracks nucleated in less than one hour of hydrogen charging at specific non-metallic inclusions and not necessarily the largest ones as commonly thought. It is observed that the HIC cracks propagated by a quasi-cleavage mechanism in transgranular paths, linking to other cracks by ductile tearing. However, after a few hours of hydrogen charging, the crack growth rate dropped to almost zero, and the overall HIC growth was due almost solely to the interconnection of previously formed individual cracks. The examination of the in-service failed pipe showed similar fractographic and growth characteristics as compared to the laboratory-induced ones. It showed that HIC was little affected by the primary stresses and the proximity of other defects and structural discontinuities.
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