How should the fillet weld joint structure between composite panels be selected?
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This post was last edited by Slay demons and evil forces on 2019-4-24 at 10:17. There are currently 5 storage tanks, with a diameter of around 12 meters. The material is 316L; it was originally designed as stainless steel. Later, the client requested a reduction in costs and asked for the use of Q235B+316L composite steel plates. We have also built composite plate storage tanks before. However, the bottom plates of the tanks are all made of pure stainless steel. Now, in order to standardize the material specifications and facilitate bulk ordering of composite panels from the manufacturers, as well as to save costs, the owners require that the tank bottoms be made of composite panels as well. The structure shown in the drawings provided by the design agency is as depicted below, and it is identical to the fillet weld structure at the bottom of the stainless steel storage tank. Later, the owner reviewed the drawings and specified that for the structure shown in the drawings, the outside part should be welded with stainless steel and carbon steel, while the inside part should be welded with stainless steel to stainless steel. First, for the fillet welds of composite panels, can strength be ensured without beveling? After all, the fillet welds at the bottom of the tank are subject to severe stress. Second, the outer side is welded with stainless steel and carbon steel, using fillet welds – is such welding feasible? Subsequently, the design firm modified the drawings to adopt the structure shown below. The owner’s feedback after reviewing the drawings was that this structure features grooves in the bottom ring wall panels, resulting in composite welds whose strength is greater than that of the original design. However, the stainless steel coating on the bottom plate of the tank should be planed off before welding, and then stainless steel should be surfaced welded on. The construction party was not very willing, saying that the diameter of the tank is large and that doing this would be too troublesome. The design team deemed it unnecessary; the composite panel was selected as grade B1, and its bonding strength is essentially the same as that of pure stainless steel. There is no need to remove the cladding; welding can be done directly on the surface of the cladding. What are everyone’s thoughts on these two structural options as well as the owner’s opinions?
@taozb @wanlirn @Douman
I agree with the owner’s opinion. The stress conditions on the fillet welds at the bottom of the tank are quite severe; if composite plates are to be used, it is necessary to ensure that welding occurs between carbon steel and carbon steel in this area, and the composite layer must be removed. Just as in tower structures with composite panel constructions, all the main load-bearing beams inside need to be removed; it’s not sufficient to consider only composite panels of grade B1. With such a large amount of welding in the fillet welds, the contraction stresses could cause the composite layers to separate on their own.
That’s what I mean, but there’s no need to weld stainless steel onto the outer edge plates of the tank; however, it’s important to take care of the local welds to prevent carbon steel electrodes from being used when welding on stainless steel.
There’s no need to weld stainless steel onto the outer edge plate of the tank, but the local welds need to be properly treated. How should that be done?
Yeah, if no surfacing is done, it becomes a water storage tank, and this type of structure is difficult to work with; it’s better to use surfacing with a transition material.
A transition material is weld-on the outside of the fillet weld; what about the inside? Should a transition layer be welded first and then a coating layer?
Yes, internally, it is necessary to ensure corrosion resistance, following the sequence of carbon steel welding, transition layer, and cladding.
What does the transition layer of a fillet weld look like? Is there an illustration?
The so-called transition layer is created by using high-chromium-nickel welding materials such as A307 for welding the transition portion, and then using the same welding materials as those used for the cladding material to weld the surface layer such as A107