Browsing by Author "Billingham, J."

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    An investigation into the fatigue and corrosion fatigue properties of two high strength low alloy steels and their HAZ’s.
    (1992-11) Drury, J. A.; Billingham, J.; Spurrier, J.; Hockenhull, B. S.
    Testing was performed on three point bend specimens machined from parent plate and welded samples machined such that the crack propagated down the heat affected zone. Specimens were subjected to tension-tension loading using a stress ratio of 0.6 and a testing frequency of 0.5 Hz. Tests were performed in air and in a synthetic sea water solution. Three levels of corrosion protection were investigated, freely corroding, protected at -800 mV and over protected at -1100 mV. The resulting crack growth rate data were plotted on a log scale against the log of the stress intensity range. This made comparisons between different conditions and materials easier. Both high strength steels and the heat affected zones associated with their weldments compared favourably with BS4360:50D structural steel when tested in air and with a cathodic potential of -800 mV. Using over protection conditions the materials showed a susceptibility to hydrogen concentration. A particularly sensitive technique was used to investigate the effects of heat affected zone microstructures on the crack propagation rate. This was achieved using a continuous monitoring gauge mounted onto the side of the specimen. The gauge was used to obtain the crack length and a computer was coupled to the fatigue machine to control the applied loads. The resulting data showed that there was a variation in growth rates between different weldment regions which was in turn influenced by the weld heat input used. The other finding was that when low heat inputs were used for welding there was rapid increase in crack growth rate associated with the coarse grained region, which was attributed to the aligned carbides of this region which act to stop crack blunting. This effect was only seen in the 1.5 kJ/mm weld, higher heat inputs cause a break up of these carbides and hence the crack is able to blunt.
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    Metallurgical investigation of hyperbaric welding at pressures to 250-bar for repairs to deep sea pipelines
    (Cranfield University, 2001-10) Nosal , P. E.; Billingham, J.
    Abstract not available
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    A study of fatigue crack propagation in quenched and tempered and controlled rolled HSLA steels.
    (Cranfield University, 1987-09) Callister, D. R.; Billingham, J.; Hockenhull, B. S.
    A range of HSLA steels reflecting the two major processing routes, quench and tempering and controlled rolling, have been tested in fatigue to assess their potential wider application in the offshore Industry. The six steels chosen have a wide range of yield strenghts (470 to 690Nmm-2), fracture toughness (31 to 260J at -40°C) and carbon equivalent values (0.19 to 0.33). Fatigue testing has in general been carried out at low frequency (0.5Hz) and high load ratio (0.6) however some tests have been conducted at very low frequency (0.1Hz) and low load ratio (0.1). An in-air study was first used to assess the fatigue performance of all six parent plates. Five steels were welded by the Submerged Arc Welding process at high heat input (1.5kJmm -1) to evaluate the Heat Affected Zone (HAZ) fatigue performance. A new test was devised to grow a fatigue crack through a single pass, bead on plate-, HAZ whilst maintaining a constant stress intensity range. The surface crack length was continuously monitored and recorded to an accuracy of 0.01mm. A corrosion fatigue study evaluated the performance of one controlled rolled and one quenched and tempered steel at three levels of impressed current cathodic protection. Extensive metallographic examination was made to study the influence of microstructural features and types on fatigue crack propagation. Techniques used include optical microscopy, scanning electron microscopy, fatigue crack and surface replication and crack profile digitising. These techniques give an assessment of crack path deviation and branching, the influence of precipitates and inclusions, and an indication of the mode of fatigue crack propagation. The wide range of microalloyed HSLA steels tested have shown a significant improvement in fatigue crack propagation resistance over structural steels conforming to BS 4360 grade 50D. Typically an improvement by a factor of two has been observed. Whilst the observed increase in fatigue life was slightly reduced by high heat input welding the slope of the Paris curves remained unaffected thus indicating a similar stress intensity range sensitivity in the HAZ to that shown by the parent plate. The newly developed crack monitoring system coupled to a computer controlled fatigue testing machine has shown a wide variation in fatigue crack propagation rates through a heat affected zone microstructural gradient. Growth rates have increased by a factor of ten in localised coarse grained microstructural regions compared to the adjacent weld metal and outer heat affected zone. The corrosion fatigue study has also indicated that in general HSLA steels retain their superiour fatigue resistance compared to structural steels and in particular respond more favourably to cathodic protection. Both in-air and corrosion fatigue studies have indicated that the controlled rolled steel microstructures developed mainly for line pipe application has the greatest potential for increased use offshore.