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Being corrosion resistant, light weight, and easy to install at relatively low cost, Reinforced Thermoplastic Pipe (RTP) is now increasingly being used for offshore operations. RTP pipe in this study is mainly composed of three layers: a wound high strength fiber reinforced layer to improve the resistance of the pipe to internal pressure; a plastic inner layer to transport fluid; a plastic outer layer to protect the pipe. A precise calculation of the burst strength of RTP pipe will be useful for the safe use of RTP pipe’s internal pressure resistance. The Finite Element Analysis (FEA) method and mathematical analysis are employed to study the properties of pipe under internal pressure. The Finite Element Analysis method is used to simulating the pipe under increasing internal pressure using ABAQUS. The model is established with the conventional shell element, and the anisotropic property of plastic is also considered in the model. In the mathematical analysis, the reinforcement layer of the pipe is assumed to be anisotropic and other layers are assumed to be isotropic. Based on the three-dimensional (3D) anisotropic elasticity theory, an exact elastic solution for burst strength of the pipe under internal pressure has been studied. This paper focus on the calculation of RTP pipe’s burst strength, using mathematical approach and FEA approach, on the basis of elaborated study of RTP pipe’s failure process. Our results from mathematical and FE simulation agree each other for burst pressure of the RTP pipe. Our FEA models are also compared with the experimental research in order to validate our FEA models.

Underwater wet welding (UWW) is widely used in repair of offshore constructions and underwater pipelines by the shielded metal arc welding (SMAW) method. They are subjected the dynamic load due to sea water flow. In this condition, they can experience the fatigue failure. This study was aimed to determine the effect of water flow speed (0 m/s, 1 m/s, and 2 m/s) and water depth (2.5 m and 5 m) on the crack growth rate of underwater wet welded low carbon steel SS400. Underwater wet welding processes were conducted using E6013 electrode (RB26) with a diameter of 4 mm, type of negative electrode polarity and constant electric current and welding speed of 90 A and 1.5 mm/s respectively. In air welding process was also conducted for comparison. Compared to in air welded joint, underwater wet welded joints have more weld defects including porosity, incomplete penetration and irregular surface. Fatigue crack growth rate of underwater wet welded joints will decrease as water depth increases and water flow rate decreases. It is represented by Paris's constant, where specimens in air welding, 2.5 m and 5 m water depth have average Paris's constant of 8.16, 7.54 and 5.56 respectively. The increasing water depth will cause the formation of Acicular Ferrite structure which has high fatigue crack resistance. The higher the water flow rate, the higher the welding defects, thereby reducing the fatigue crack resistance.

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Low carbon steel was coated by hot-dipping into a molten Al-10%Si bath. The high-temperature oxidation was performed at 700oC for 1 h to 49 h in air, air +100% H2O, and air + 30% ethanol under atmospheric pressure. An elemental composition distribution, morphologies of the aluminide layer and the oxide scale were characterized by OM, XRD, and SEM/EDS. After hot-dipping treatment, the coating layers consisted of Al, Si, FeAl3, τ5-Fe2Al8Si, and Fe2Al5. The results of high temperature oxidation tests showed the oxidation rate were parabolic law in three different atmospheres. The polyhedral τ1-(Al,Si)5Fe3 formed at a short time oxidation completely transformed to FeAl2 and FeAl due to the composition gradient and the chemical diffusion. The effect of water vapor on the oxidation resistance of the Al-Si coating may be attributed to increase in Al and Fe ions transport, leading to loss of protective aluminide layer by formation of iron oxide nodules on the coating surface and at interface between aluminide layer and the steel substrate.