Flexible risers are critical equipment for the production of oil and gas in offshore fields around the world. The annulus region may condense acidic water containing H2S exposing the tensile armour ...steel wires to a sour environment, which may promote sulphide stress cracking (SSC) and/or hydrogen-induced cracking (HIC). This work aims to evaluate through electrochemical and constant displacement tests the effectiveness of thermal spray aluminium (TSA) coating to mitigate SSC and HIC in high strength steel used to manufacture the tensile armour of a flexible riser. Electrochemical tests confirmed the anodic behaviour of the coating against the steel and estimated a service life of 2.5 years. The constant displacement test indicated that the non-coated samples failed by SSC although some cracks were also found in the samples mid-section due to HIC. For Al-coated samples, no signs of SSC and HIC were observed. The TSA coating showed a dual barrier effect, hindering either corrosion of steel or hydrogen up-taking, and neither SSC nor HIC was observed. Samples with a coating defect were cathodically protected and no HIC was observed.
•Non-coated steel failured by sulphide stress cracking (SSC) and showed cracks associated to hydrogen-induced cracking (HIC);•Thermal spray aluminium (TSA) coating suppressed SSC due the barrier effect and the cathodic protection;•TSA limited the hydrogen diffusion which hindered the HIC.
The hydrogen diffusion and trapping in AISI 4330 V high-strength steel is investigated by repetitive electrochemical hydrogen permeation tests, thermal desorption analysis, and hot and melt ...extraction. The analysis is coupled with a numerical model based on McNabb and Foster's kinetics with varying degrees of trap occupancy. The trapping parameters are obtained by fitting the numerical model to the experimental data, which permits to describe the diffusion and trapping processes for all tested conditions. In addition, the predictions calculated by the model are critically discussed and compared with those derived from usual approaches based on analytical solutions from Fick's laws and from Choo and Lee's method. An important difference is observed, indicating that the use of general analytical methods may not be adequate in the case of the studied steel. The use of more rigorous analysis provides a better understanding of trapping phenomenon and improved predictions of charging times and contents.
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•Hydrogen diffusion and trapping in AISI 4330 V steel is investigated.•Numerical model was applied to simulate the diffusion and trapping processes.•Estimates based on effective diffusion coefficient and numerical model are compared.•Numerical approach is compared with Choo and Lee's method for TDA.•The density and detrapping activation energy of traps in AISI 4330 V are determined.
Titanium matrix composite (TMC) has demonstrated a high strength-to-weight ratio as well as good properties at high temperature. The successful application of TMC depends on a suitable joining ...technique. Rotational friction welding seems to be an ideal choice because it is a solid state joining process (TMCs have shown to be sensitive to fusion welding processes) achieving good mechanical properties. The aim of this work is to investigate the feasibility of joining particle-reinforced composites by rotational friction welding. The integrity of the joints has been investigated by optical and electron microscopy, while the mechanical properties assessment included microhardness and tensile tests. The mechanical properties assessment has indicated no detrimental effect of the joining process on the tensile properties.
