Electron-beam powder-bed-fusion additive manufacturing was used to build Ti6Al4V blocks. Postfabrication thermal treatments were applied to modify the mechanical properties. The postfabrication treatments included hot isostatic pressing and solution treatment and ageing. The microstructure and mechanical properties of the as-built and postthermally treated material were characterised. The postfabrication treatments were found to be effective in homogenising the microstructure and reducing the number of defects/pores, which improved the material Charpy impact toughness and fatigue life with some reduction in the material's strength. Based on the present results, as well as data from previous literature studies, the reduction in material strength after the postthermal treatment is likely to be caused by the combined effect of α-lath coarsening and the low oxygen content of the powder feedstock.

No abstract

No abstract

Pipes that experience sour service need to resist that corrosive environment. One method for achieving corrosion resistance is by lining the inside of the pipe with a corrosion resistant alloy (CRA), such as stainless steel or a nickel based alloy. This has the advantage of being much cheaper than either making the pipe from the CRA or metallurgically bonding CRA to the pipe (ie clad pipe). Lined pipe is gaining popularity, and has so far been used successfully in applications where applied strain levels are low, however more data is needed on its fatigue strength and its behavior when subjected to high levels of applied strain. A Joint Industry Project (JIP), funded by Petrobras, BG Group, Saipem, Tenaris, Technip, Cladtek and HMC, was run by TWI Ltd and INTECSEA to investigate and generate data on CRA lined pipe. The JIP included full scale resonance fatigue testing, allowing the failure location of lined pipes to be investigated, development of an ultrasonic inspection procedure for lined pipe, small scale mechanical tests to generate materials data and calculation of stress intensity factors specific to the lined pipe geometry. This paper presents a summary of the work carried out. The significance of the paper is that it describes a body of work carried out in the field of CRA lined pipe, helping operators and those at the front-end engineering design (FEED) stage to choose lined pipe, with the resulting cost savings.

Now that bolted flanges rather than grouted connections are used to join the transition piece to the monopile in offshore wind turbine towers, many large bolts are being used in applications which subject them to fatigue loads. The bolts in these ring flanges are typically M64 or M72 in size (ie 64mm of 72mm nominal diameter). The fatigue design codes, BS 7608, DNVGL-RP-C203 and Eurocode 3 do provide S-N curves for threaded fasteners, but the reference diameter in those documents is 25mm or 30mm. A thickness correction is provided, to account for larger diameter bolts, but this was originally derived by analysis of the performance of welded joints. It is unclear whether the S-N curves and the recommended thickness correction are appropriate for larger diameter threaded fasteners. The offshore wind industry usually specifies hot dip galvanised bolts, to provide some corrosion protection in the offshore environment. Again, there is uncertainty over whether the S-N curves in fatigue design standards apply to bolts with a galvanised coating. Since the fatigue design codes provide S-N curves for air, free corrosion or seawater with cathodic protection, it is also unclear which of these should be used to predict the fatigue performance of bolts with a galvanised coating. In order to provide data to address these uncertainties, hot-dip galvanised, grade 10.9, M72 bolts from two manufacturers were tested in both air and a seawater environment. In order to represent the conditions experienced by bolts in internal ring flanges, the artificial seawater was sprayed onto the bolts during testing. Tests were conducted with a mean stress corresponding to 70% of the specified minimum 0.2% proof strength of the bolts. Tests were also performed in air, on uncoated M72 bolts, and uncoated M64 bolts for comparison. The results suggest that the current thickness correction in DNVGL RP C203 and BS 7608 is appropriate for M72 bolts. The results in air from the galvanised bolts were below those from uncoated bolts. Although the galvanised results were above the thickness corrected in-air standard design curves (BS7608 Class X -20%, DNVGL Class G and DNVGL ST 0126 FAT 50), they were below the mean curves, suggesting that the performance of galvanised bolts is slightly lower than the existing recommendations.