1 Introduction
The underwater Welding Electrodes first appeared in 1917, British Navy shipbuilding used underwater electric arc welding stanch ship riveted seams and rivets leaking part. The late 1960s, especially with the development of offshore oil and gas, marine engineering structural fatigue, corrosion or accident damage an urgent requirement for underwater welding repair, and to achieve a better quality of welding, thus greatly promoted the underwater Development of welding. This is the first reported 1971 Humble Oil drilling platform in the Gulf of Mexico underwater welding repair work. As technology advances, underwater welding and cutting repair technology has been widely used in marine engineering structures, subsea pipelines, ships, docks and port facilities.
Underwater welding can be divided according to the environment in which the welding arc and diving welders job underwater wet welding, underwater welding and underwater dry local dry welding three. The underwater SMAW are underwater wet welding, compared with the dry underwater welding and local dry welding, underwater SMAW has good flexibility and mobility, short operating time, the welding equipment is simple and does not require costly advantages of auxiliary equipment and facilities, and the economy is good.
2 factors affect underwater SMAW weld quality
Although wet welding has many advantages, but because of the presence of water in the wet-around the weld zone, under the influence of the water pressure so that the welding process and operation occurs many difficulties, and local dry dry underwater welding and underwater welding compared to underwater wet welding, weld quality is poor. Which affect underwater SMAW weld quality factors are mainly the following points:
2.1 visibility poor
Since water light has a strong absorption and scattering, so the same intensity of light in the distance from the irradiation of the water than in the air in the irradiation distance is much smaller. Further around the welding arc generated a large number of bubbles and haze floating, so that the water to become disordered and turbid, so that the welding when the visibility is poor, thus diving welder is difficult to see the reactions of the arc and weld pool, in this case belongs Blind welding, diving welders difficult play operation skills, could easily lead to a variety of welding defects, it is difficult to guarantee the quality of underwater welding.
2.2 weld hydrogen content
The content of hydrogen in the metal exceeds the allowable value, it is possible to make the metallic material generating hydrogen harm caused cracks, pores, resulting in the destruction of the structure. Underwater welding the amount of hydrogen in the arc when compared to the air, and the partial pressure of hydrogen compared to the air in the high, which makes a lot of dissolved hydrogen in the weld, so that the ductility and toughness of the welded joints is poor welded joints could easily lead to welding cracks, reducing the performance of the welding of metallic materials.
2.3 weld cooling fast
Underwater electrode arc welding, the arc around the inflatable bag is very small, just solidified with the movement of the airbags, the weld metal during the Carbon Steel Welding Electrode process, but is still in the red-hot state directly into the water, since the water's thermal conductivity coefficient than air many times greater, so the weld metal is quenched easily quenched appears the high hardness of the tissue, which is many of the good performance of welding metal under atmospheric pressure to the underwater on difficult to weld of the important reasons.
2.4 welding arc instability
Underwater electrode arc welding, the arc, although not directly in the water combustion, but the arc is directly affected by the effects of water and pressure. As the pressure increases, and water, the cooling effect of the arc contour contraction, the arc voltage increases, so the arc combustion instability. In addition, underwater welding job, affecting underwater welding arc stability factors include inrush current surface wind and waves and underwater, divers wear a wetsuit and counterweight, and divers diving technology and welding technology, etc. These factors will lead to the loss of the diver's body balance and stability, thereby affecting the stability of the underwater welding arc. Unstable arc welding, weld quality is also very difficult to guarantee.
The 2.5 underwater clean-up and open beveling difficult to be carried out
Cleanup onshore before welding, underwater more difficult to carry out the work of the clean-up of the weld and open groove, the methods and tools used by small underwater weld surface often cleaning is not clean, open groove of less than the standard of the welding groove, so underwater electrode arc welding often impervious slag, porosity, and weld defects, it is difficult to ensure the quality of the welding.
3 Suggestions to improve underwater weld quality
Underwater SMAW the weld prone welding defects, stress concentration, so difficult to control the quality of welded joints, and generally can not be used underwater metal welding materials structure. This welding method is more flexible, simple, wide adaptability, construction and low cost, so some of the more important marine structure, can also to this underwater welding method can be used for welding.
To ensure the quality of underwater SMAW welding, the following aspects need attention and improvement:
3.1 diving welders should be proficient diving technology
Construction of underwater operations, diving technology is only mastered the basics diving and underwater diving skills, maintain a good stability of the underwater body weld to weld a qualified. Diving techniques, diving apparatus selected auxiliary equipment wear, underwater balance ability training, as well as a variety of dangerous situations the reasonable disposal are key to ensure that the quality of underwater welding. Such as water, divers should choose (such as TF-3 diving harness) better weight latent harness, and proper installation the baffle and work platform, to maintain security and stability of the divers; operating depth is not smooth flow lightweight KMB-28 or MZ-300 harness mainly, due to wear the pressure lead and auxiliary equipment, to ensure flexibility of divers, underwater weld quality.
3.2 dive underwater SMAW welders mastered the basic knowledge and skills
Diving welders in concrete construction work before the system theory of learning and underwater welding real training, formal induction through the examination of the relevant subjects. Through learning and training qualified diving welders should understand and master the knowledge of the structure and material being welded, familiar with the structure of the welding equipment, connect and use, to grasp the basic characteristics of the underwater welding rod. Underwater welding job, able to carry out the installation of underwater welding rod, arc, op bars, finishing and connection operations on specific welding parameters can be the right choice, the understanding of a variety of underwater welding job security Precautions.
3.3 increase of diving apparatus, underwater welding equipment and welding materials, tools to improve and develop underwater clean-up and open groove
China's diving harness, welding equipment and materials and underwater clean-up tool can basically meet the needs of the underwater welding job, but there are still many shortcomings compared with foreign countries, worthy of improvement and perfection. Such as in diving apparatus, in order to avoid the arc diver eyes, should increase in the phreatic surface out of the window one can open a tinted glass mirror, the mirror can not only protect the eyes of the diver when the diver normal diving operations, in clear water the time also allows divers observed the welding arc and weld better ensure the quality of the welding.
Underwater welding equipment and welding materials, such as the development of lightweight, stable output inverter welding machine instead of the current silicon rectifier or SCR arc welding rectifier; improved welding cables insulated rubber layer to reduce the weight of the cable, enhanced insulation protective effect, improving the ability of anti-corrosion and anti-friction; to improve underwater welding to the structure, to improve the security and flexibility of use; improved the composition of the electrode coating and waterproof layer to improve the performance of electrode waterproof, anti-stomata and crack , ease of ignition, and increase the stability of the arc.
Automated tools such as the research and development of pneumatic or hydraulic wheel-based tool to clean up and open groove in front of the underwater welding, to ensure that these tools can not only be used in simple structure, but also in a number of complex and Important structural applications, really good job in the work of the clean-up and open groove before welding, to avoid the emergence of weld defects.