Regarding the selection of welding materials
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Our project supplies steam to external users in the form of pre-fabricated directly-buried steam pipes, with an inner pipe made of 20#, and an outer pipe made of spiral-welded Q235B steel. The design institute provided us with J427 as the welding material for our welding designs. One of our technicians suggested using J507, stating that its price is similar to that of J427, but it performs better, results in a higher success rate in inspections, and is also easier to obtain. I’m not sure if this statement is correct Dear sea friends, is there anyone who is familiar with welding materials? Or are there any relevant guidelines suggesting which welding materials should be used for welding which types of materials? Also, for our inner tube, we plan to use TIG welding for the root pass and welding with a regular welder for the finish pass; so what material should be used for TIG welding? So, there’s no need for TIG welding as a base layer for the outer tube; just beveling it and then welding it is sufficient, right?
For welding the inner tube, 427 is a suitable choice. There is no claim that the qualification rate of 507 electrodes is higher than that of 427 electrodes. If the outer spiral welded pipe is used as a casing, no testing requirements apply; in such cases, 422 electrodes can be used, or 427 electrodes as well
Use TIG-J50 wire for TIG welding; it’s more convenient than H08Mn2Si, and the price difference isn’t significant
427 is a suitable choice for inner tube welding.
The outer tube also has inspection requirements: 100% UT, while the inner tube requires 100% RT. So, for root welding of the inner tube using TIG welding, which wire is good? Use 427 for the cover. For the outer tube, ordinary welding is sufficient; use 427 as the welding material as well. Should I use TIG-J50 or H08Mn2Si for TIG welding wires? Or something else?
Using 427 for inner tube welding is the right choice
When using TIG welding for the root pass, what type of wire is suitable for TIG welding?
Your instructor’s approach is a bit biased; the design institute recommends equal-strength matching, while the instructor opts for high-strength matching. The J427 and J507 welding electrodes are of the same type. They are all low-hydrogen wax-type flux-cored welding electrodes. The weldability is roughly the same. TIG welding is used for root pass welding mainly due to its good welding processability and stability. And there is very little slag. Using welding rods for the root pass is troublesome due to slag removal, and defects are likely to occur in subsequent processes. If it is said that there are indeed differences in operability between J422 and J507. One is an acidic welding electrode, and the other is an alkaline welding electrode. The J422 welding rod has good operability and fluidity. The J507 welding rod has good impact resistance.
My suggestion to the design institute is to use TIG welding for the root pass, with H08Mn2SiA. For welding the cover layer, 427 electrode is used; I’m not sure if there’s any problem with that.
1. Using argon arc for the base layer and manual welding for the finishing layer is a fairly good technique； 2. There is no need to use J507; it has much higher strength
No problem, it’s very sensible advice – balancing quality and efficiency.