Microstructure Evolution and Mechanical Properties of Underwater Dry and Local Dry Cavity Welded Joints of 690 MPa Grade High Strength Steel

Abstract

Q690E high strength low alloy (HSLA) steel plays an important role in offshore structures. In addition, underwater local cavity welding (ULCW) technique was widely used to repair important offshore constructions. However, the high cooling rate of ULCW joints results in bad welding quality compared with underwater dry welding (UDW) joints. Q690E high strength low alloy steels were welded by multi-pass UDW and ULCW techniques, to study the microstructural evolution and mechanical properties of underwater welded joints. The microstructure and fracture morphology of welded joints were observed by scanning electron microscope and optical microscope. The elemental distribution in the microstructure was determined with an Electron Probe Microanalyzer. The results indicated that the microstructure of both two welded joints was similar. However, martensite and martensite-austenite components were significantly different with different underwater welding methods such that the micro-hardness of the HAZ and FZ in the ULCW specimen was higher than that of the corresponding regions in UDW joint. The yield strength and ultimate tensile strength of the ULCW specimen are 109 MPa lower and 77 MPa lower, respectively, than those of the UDW joint. The impact toughness of the UDW joint was superior to those of the ULCW joint.

Dissimilar underwater wet welding of HSLA steels

“…In this method, the welder is in the water, but the areas of welding and joint are isolated from the environment by a small chamber, in which the welding gas removes the water outside. This phenomenon produces conditions similar to the hyperbaric dry welding but does not require building any expensive chamber [20,21]. The last is the most popular and the cheapest method of underwater welding which is known as wet welding.…”

Advantages of the Application of the Temper Bead Welding Technique During Wet Welding

“…The second method is welding with the use of a local dry chamber. In this method, the diver/welder is in direct contact with the water, but the welding area is located in a special chamber that isolates this area from the surrounding water environment [6,7]. The final and most common method of underwater welding is wet welding, where the diver and welding area are in contact with the water environment.…”

Microstructure and Mechanical Properties of Underwater Laser Welding of Titanium Alloy

“…Underwater welding (UW) turns into the dominating means of maintenance, which was used in offshore pipelines and platforms, vessels, seashore components, as well as port equipment and systems [4]. As reported by Shi and Łabanowski, there are three kinds of underwater welding processes, including underwater dry welding (UDW), underwater wet welding (UWW) and underwater local dry cavity welding (ULDCW) [4,5]. UDW is usually implemented in an underwater high-pressure chamber and can obtain high-quality welded joints, but in comparison to UWW, the welding equipment of UDW is complex and expensive, extremely [6].…”

“…During ULDCW, the water of a small scope is drained to form a local dry cavity, making the welding process steady. Therefore, in comparison to UWW, this means it can obtain higher-performance welded joints, besides, it is cheaper and more convenient than UDW [4]. Shi et al investigated the welded joints of high strength steel via UDW and ULDCW.…”