What type of welding materials should be used for welding S235JR steel pipe?
It is recommended to use E43 series welding rods, such as E4315 or E4316, for welding S235JR steel pipes. This type of welding materials has a good match with the mechanical properties of the parent material. For gas shielded welding, ER70S-6 welding wire can be used with 80%Ar+20%CO₂ mixed gas to obtain stable welding quality. For submerged arc welding, H08A welding wire should be used with SJ101 flux, which is particularly suitable for welding thick-walled pipes. When selecting welding materials, special attention should be paid to the fact that the carbon equivalent of the deposited metal should be controlled below 0.4% to ensure good weldability. For important structures, it is recommended to conduct welding process assessment tests to determine the optimal welding parameters.
What preparations need to be made before welding S235JR steel pipes?
Before welding, impurities such as oil, rust, and scale within the area to be welded and the surrounding 20mm range must be thoroughly removed. For steel pipes with a thickness of more than 10mm, it is recommended to open a 30-35° V-shaped groove and leave a blunt edge of 1-2mm. When the ambient temperature is lower than 5℃, preheating measures should be taken, and the preheating temperature should be controlled within the range of 80-120℃. Before welding, the ovality of the steel pipe end face should be checked and corrected if necessary to ensure that the butt gap is uniform. Appropriate arc-starting plates and arc-ending plates should also be prepared to avoid defects caused by direct arcing on the parent material.
How to control heat input when welding S235JR steel pipes?
Welding heat input should be controlled within the range of 15-25kJ/cm. Excessive heat input will cause coarse grains in the heat-affected zone. For thin-walled pipes (t≤6mm), it is recommended to use low-current rapid welding, and the interlayer temperature should be controlled below 150℃. When welding thick-walled pipes, multi-layer and multi-pass welding should be used, and the thickness of each weld should not exceed 4mm. Using pulsed MIG welding can effectively control heat input and reduce welding deformation. It is particularly important to note that the heat input of the last layer of weld should be appropriately reduced to improve the weld surface formation.
How to detect the quality of S235JR steel pipe welds?
The appearance inspection requires that there are no defects such as cracks, pores, undercuts, etc. on the weld surface, and the excess height is controlled within the range of 0-3mm. For important structures, 100% ultrasonic flaw detection should be carried out and evaluated according to EN ISO 17640 standard. Radiographic testing is suitable for detecting internal defects and is usually carried out according to EN ISO 10675-1 standard. Hardness testing requires that the hardness of the weld and heat-affected zone does not exceed 280HV10. For structures subjected to dynamic loads, macroscopic metallographic inspection is also required to evaluate the quality of the fusion line and heat-affected zone.
Does S235JR steel pipe need heat treatment after welding?
In general, S235JR steel pipe does not need heat treatment after welding because of its low carbon equivalent and good weldability. However, for important structural parts with a thickness of more than 30mm, it is recommended to perform stress relief annealing at 550-600℃. When constructing in cold areas (ambient temperature below -10℃), slow cooling measures should be taken after welding, such as covering with insulation cotton. For galvanized steel pipes, welding will damage the zinc layer, and the weld area needs to be re-treated for corrosion protection after welding. It is particularly important to note that any post-weld heat treatment must strictly control the temperature and time to avoid affecting the mechanical properties of the material.
