Abstract:The desire to model a control system so as to optimize the welding process parameters and the effect of the environment during underwater wet welding makes it necessary to study the effects of these parameters as it affects the weld bead geometry of welds achieved in underwater welding. The objective of this paper is to analyze how welding arc current, voltage, speed, and the effect of the water environment affect the weld bead geometry such as bead width, penetration, and reinforcement height. Comparing the differences of the effects of welding input parameters for air and wet welding as it affects the welding output quality parameter is the method employed in this research paper. The result of this study will give a better understanding of applying control mechanism in predicting the quality of a weld during underwater welding. A clearer insight of the weldability of structural steels for offshore applications as it relates to underwater welding, having a full knowledge of the nonlinear multivariable parameters is indicative of better control methods.

Abstract:It is important to achieve high quality weld in underwater welding as it is vital to the integrity of the structures used in the offshore environment. Due to the difficulty in ensuring sound welds as it relates to the weld bead geometry, it is important to have a robust control mechanism that can meet this need. This work is aimed at designing a control mechanism for underwater wet welding which can control the welding process to ensure the desired weld bead geometry is achieved. Obtaining optimal bead width, penetration and reinforcement are essential parameters for the desired bead geometry. The method used in this study is the use of a control system that utilizes a combination of fuzzy and PID controller in controlling flux cored arc welding process. The outcome will ensure that optimal weld bead geometry is achieved as welding is being carried out at different water depth in the offshore environment. The result for the hybrid fuzzy-PID gives a satisfactory outcome of overshoot, rise time and steady error. This will lead to a robust welding system for oil and gas companies and other companies that carry out repair welding or construction welding in the offshore.Keyword: Control System, Bead Geometry, Fuzzy Logic, Process Parameter, Underwater Welding BackgroundOwing to the environmental conditions in which structures operate in the offshore, it is important that a high structural integrity is guaranteed. It is evident that structural failures can arise as a result of poor weld quality and other mechanical properties of the loaded structures operating in the offshore. The quality of welds achieved underwater experience a major setback because of the unique feature of the weld metal fast cooling rate and other factors such as the stability of the welding arc, loss of alloying elements and difficulty of a good visibility to weld underwater. This research paper addresses the issue of controlling the welding parameters at different water depth in achieving a desired weld bead geometry that is reasonably satisfactory of the weld quality that can operate in the offshore. A control mechanism which incorporates the design advantages of fuzzy logic control and PID control is implemented in this study. Experimental data to be analyzed in this paper is adopted from the work of Chon L. Tsai et. al. It is a wellknown fact that high cooling rate and hydrogen embrittlement are characteristics of underwater wet welding (UWW). Rapid cooling mechanism and their effects have been studied by Chon L. Tsai and Koichi Masubuchi [1]. The final microstructure of the heat affected zone (HAZ) for a given material is determined by the composition, peak temperature and cooling rate. It is possible to control the weld metal composition, the peak temperature and the cooling rate to yield favorable microstructure. However, it is not possible to control the composition of the HAZ of the parent material. Fast cooling effect of the water environment in UWW results in a martensitic heat affected zone having high hardness and poor notch...

Background: The structural integrity of welds carried out in underwater wet environment is very key to the reliability of welded structures in the offshore environment. The soundness of a weld can be predicted from the weld bead geometry.