Regarding takeover welding issues
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In actual production, after welding the outer seam of the nozzle and the fillet weld of the cylinder, we ask whether the inner seam is welded or not. Why is it often marked as single-sided welding in the welding joint schematic diagram of the drawing?
If the diameter of the cylinder is large, double-sided welding is the best. However, the manufacturer often only welds on one side to save trouble. If we design, we must strictly follow the requirements. If something goes wrong, it's theirs too.
This generally depends on the type of weld bevel. If the pipe diameter is large or the equipment has a manhole, it is basically double-sided welding. Moreover, even if it is single-sided welding, the pressure vessel must be a fully welded structure.
Ensure welding penetration. Use argon arc welding to seal the back, and single-sided welding can also ensure quality.
What was said above is good. After the double-sided groove is made on the design drawing, if double-sided welding cannot be conveniently performed, TIG welding must be used to ensure full penetration. For Class D welds that can achieve double-sided welding (when nozzles, manholes, reinforcing rings, etc. are welded to the cylinder), double-sided welding must be performed according to the design drawings.
The poster talked about large pipe diameters, that is, small pipe diameters > 20MM. The clear answer is to use 50mm pipes. The 50° groove does not require argon arc welding. Can the quality of single-sided manual welding be guaranteed? Why do drawings often show single-sided welding diagrams? Isn't the welding penetration in general production not considered?
There are many factors that affect whether single-sided welding or double-sided welding: 1: The requirement for full penetration, there is such a requirement in the standard, but there is also a saying that "single-sided welding can achieve the same quality as double-sided welding", so it does not mean that double-sided welding is better than single-sided welding. 2: If the welding space, the welding space is small, or inaccessible and other factors affect the welding on the back, then single-sided welding and double-sided forming are used. 3: Welding deformation, For those large openings on the cylinder, it is best to use double-sided welding to prevent serious collapse caused by single-sided welding. 4: Corrosion factors. Welding with strict corrosion requirements generally requires that the last layer be left inside so that the weld can obtain the best corrosion resistance. In this case, double-sided welding is also required. 5: Other special requirements.
Most pressure vessels are double-sided welded, and only a few are single-sided.
Of course, whether double-sided welding or single-sided welding depends not only on design. If the manufacturing unit has mature and reliable processing and manufacturing experience, it can be used as a reference, but it must be approved by the design unit.
Personally, I understand that welders can design the welding structure according to the actual situation during the welding process without changing the basic form of the joint (such as butt joint to corner joint). Domestic welding joint forms do not necessarily have to be completely in accordance with the drawing requirements. This is similar to the instructions in HG 20583 11.11 (the clause refers to the groove size, and I understand that changing one side to double side is also within the allowed range)
You can also refer to GB985\GB986, which are the basic forms and sizes of gas welding, manual arc welding and gas shielded welding seam grooves, and the basic forms and sizes of submerged arc welding seam grooves, which are helpful to solve this problem.