Large container ships have a large ship length scale, capacity, high speed, and large openings and other characteristics, resulting in the middle area of the hull structure is at a high level of stress. As a result, large thicknesses of high-strength steel materials are often used in the design.
Single wire EGW is commonly used as a high efficiency welding method. However, generally the maximum applicable plate thickness can only reach 32~33mm, which can not be adopted on the above mentioned large thick plates;
Double-wire EGW method is generally applicable to plate thickness of up to 70mm or so, but due to the welding heat input is very large, to ensure that the performance of the welded joints to meet the specification requirements, it is necessary to use the steel plate to adapt to the large heat input welding.
Therefore, in the absence of the use of large heat input welding steel plate, large thick plate vertical butt welds can only be used FCAW multi-layer multi-pass welding, welding efficiency is low.
This method is to address the above characteristics, research and development of a combination of FCAW + EGW welding process can be applied to large thick plate welding, giving full play to its advantages of high efficiency, but also adapted to the actual characteristics of the steel plate. In other words, it is a highly efficient combination welding method that first adopts FCAW single-side welding on the structural side and realizes backside forming, and then carries out EGW welding on the non-structural side.
Key points of FCAW+EGW combination welding method
(1) Applicable plate thickness
34 ~ 80mm: that is, the lower limit is the upper limit of the applicable plate thickness of single-wire EGW; for the upper limit, a large container ship outboard inner and outer shell of the upper list of plates used is a large thickness of steel, taking into account the different thickness of different products of steel, so determine the 80mm.
(2) Thickness division
Welding thickness division principles, first of all, to give full play to the advantages of high efficiency EGW welding; at the same time must take into account the two methods of welding the amount of molten metal can not be too large a difference, otherwise it will be more difficult to control the welding deformation.
(3) Combined welding method joint form design
① Bevel angle: FCAW side in order to avoid excessive bevel width, than the normal FCAW single-sided welding bevel appropriately reduced for X ± 5 °; EGW side in order to reduce the amount of molten metal and not to bevel too wide, according to the different plate thicknesses with different bevel angles. Y±5° for plate thickness of 30~50mm and Z±5° for plate thickness of 51~80mm.
② root clearance: need to adapt to the two welding methods at the same time process requirements, that is, G ± 2mm.
③ Applicable liner form: conventional triangular liner can not meet the above joint form requirements due to angular problems, the combination of welding methods need to be used round bar liner. Diameter size needs to be selected according to the actual assembly gap value.
(4) Basic points of welding construction
Welding training. Operators need to be trained for a certain period of time, even operators with experience in EGW (SG-2 method) welding of steel plates of ordinary thickness must be trained, because the welding of thin plates and large thick plates, the operating motion of the wire in the molten pool is different.
②End inspection. The weld always ends and the part where the arc stops, non-destructive testing (RT or UT) should be used to check for defects as well as to confirm the size of the defects, remove the defects using air planing, and rework the weld using the FCAW or SMAW welding method.
③ Arc-guiding plate. The length of the lead-in plate should be at least 50mm. the lead-in plate should be of the same thickness as the base material with the same bevel. ④ welding, the wind will cause the protective gas disorder so that the weld produces porosity defects, as well as due to nitrogen intrusion in the air caused by the joint performance is low, so it is necessary to take the necessary measures to prevent wind.
