Intelligent Control Mechanism for Underwater Wet Welding

Abstract

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...

Efecto de la profundidad, la polaridad y la corriente de soldadura sobre el contenido de hidrógeno difusible con electrodos de acero inoxidable en la soldadura submarina húmeda

“…El aumento de la cantidad de hidrógeno puede provocar la aparición de grietas en el ZTA y un aumento de la porosidad. Además, las condiciones adversas en el medio acuático traen inestabilidad al arco eléctrico y el principal efecto de esta inestabilidad es un aumento de la porosidad en el metal de soldadura [1].…”

“…Se probaron profundidades de 0,3 m (profundidad del agua), 10m, 20m y 30 m. El autor también observó estabilidad en el valor de hidrógeno difusible a partir de 20 m en adelante, un aumento de la porosidad con la profundidad y la aparición de cortocircuitos a partir de 30 m en adelante. Según Omajene [1], cuando el hidrógeno está presente en mayor cantidad en la región de soldadura, con un aumento de la profundidad de soldadura, por ejemplo, hay una disminución de la estabilidad del arco. En esta situación, el hidrógeno predomina en la composición química de los gases en el interior de los poros, debido a su alto potencial de ionización, lo que dificulta el mantenimiento del arco eléctrico por la alta pérdida de energía provocada por este gas.…”