PSI - Issue 27

Ericha Dwi Wahyu Syah Putri et al. / Procedia Structural Integrity 27 (2020) 54–61 Putri et al. / Structural Integrity Procedia 00 (2019) 000 – 000

56

3

weld fatigue failure. Furthermore, it will recommend the steps for improvement and increasing the resistance of underwater weld fatigue resistance. 2. Underwater welding Underwater welding is a material welding process that is impossible doing on land. But, it carried out in the underwater. Underwater welding is often used in the river or offshore areas to repair and maintain the structure of nuclear power plants, offshore oil and gas rig, dock, and port construction (Yin et al., 2015). The application of underwater welding can use to solve problems that occur both in shallow water and at sea with a certain depth level. For the examples that occur in shallow areas are crash between ships and platforms, while problems that occur at sea with a certain level of depth are the connection of piping systems for offshore oil and gas mining (Assuncao and Bracarense, 2017). Underwater welding classified into two types, namely underwater dry welding (UDW) and underwater wet welding (UWW) (Wang et al., 2009; Hu et al., 2018). UDW is an underwater welding method carried out in a dry chamber to avoid direct contact between water and weld metal. Weld chamber made to ensure that the quality of welding results is equivalent to welding on land even though the welding process carried out underwater (Hu et al., 2018). The size and shape of the weld chamber adjusted to the dimensions of the construction to welded and the operators who will conduct welding (Majumdar, 2006). UDW has the advantage of reducing hydrogen gas from the water at the welding area, increase the strength and ductility of weld metal, improve the arc weld stability, and high corrosion resistance (Majumdar, 2006). The disadvantage of UDW is the cost required is more expensive because it requires specialized equipment compared to other methods. One of the types of equipment needed by UDW is a weld chamber. Weld chamber serves to isolation the weld metal of the welding area from the water environment. Underwater wet welding (UWW) is a welding process in which the arc weld direct contact with water in the welding area (Xu et al., 2020). UWW is an excellent method to maintain and repair construction in water because the equipment used is easy, so the operator of weld can be easy to mobilization in the water and prepared as needed before faster welding. It caused that UWW does not need a special area to weld, so it needs to be cheaper for UDW. UWW can cause a decrease in physical and mechanical properties of weld metal which is a disadvantage from UWW and is a major problem that must resolve (Guo et al., 2015). The content of hydrogen gas at UWW is greater than welding on land (Majumdar, 2006). The hydrogen gas that comes from the water around the welding area, which contains a lot of gas containing H 2 O. If the humid increase from the welding area, the more hydrogen gas dissolve in the welding metal. Surrounding air has high humidity, so it can produce welding results that are easy to crack, brittle, and easily formed porosity (Chen et al., 2020). In recent years, UWW research continues to progress and become an interesting study. Discussion topics for UWW were very various, including the microstructure of weld metal, the use of different materials, the mechanical properties of weld joints, and many others. Table 1 summarizes some of the UWW research articles that focus on the discussion of defects, inclusions, and evolution microstructure. To focus on the problem of underwater welding fatigue failure, the sorting of the topic of the article referred to in this paper is to discuss underwater welding factors that cause defects, inclusions, and changes in microstructures that are susceptible to fatigue failure.

Table 1. UWW's research with a discussion of defects, inclusions, and evolution on microstructure. No. Scholars Subjects Characterization

Findings

1.

Gao et al. (2015)

Enhancement of the fatigue strength of underwater wet welds by grinding and ultrasonic impact treatment evolution microstructure Effect of cooling rate on microstructure, inclusions and mechanical properties of weld metal in simulated local dry underwater welding

Evolution microstructure

The microstructure of underwater welding is heterogeneous, where most of the structures are PF (Proeutectoid Ferrite), Side-Plate Ferrite, and a small portion of AF (Acicular Ferrite). The process of repair at UWW can affect the microstructure of the weld metal. Heat input of 10.0 to 30.0kJ/cm, the microstructure

2.

Di et al. (2015)

Evolution microstructure and inclusions