The issue is whether to butt or lap the tank roof panels
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Recently, I worked on a small tank with a volume of 170 m3 (with a bottom plate of 10 mm thickness and wall panels and roof plates of 8 mm thickness). I created 2 drawings: one for the assembly, and one for the ladder railing. It is said that due to the small size of the containers, no detailed drawings or node diagrams are created for their design. In this way, on the assembly diagram, only an arched roof is shown; there are no melon-rind plates nor a central plate. The design specifies that the parts are welded together – meaning that the plates are first joined to form the arch-shaped roof, with no central roof plate. The bottom plates also lack any inter-plate connection method. Initially, it was said that they would be joined by welding, so shims were used for joining them; later, the supervisor suggested that lap jointing provided greater strength, and thus lap jointing was adopted instead. Background complete. Question 1: Are node diagrams and detailed drawings required for the design? Without detailed drawings and node diagrams, how can the construction team carry out the work according to the plans? Question 2.a. According to the Ministry of Chemical Industry’s catalog 02R112, the roof plates of storage tanks with a volume of 60 m3 are all overlapped, and there is a vaulted center plate. How is construction carried out in an arch structure without a central roof slab? b. Someone has previously carried out work on similar arch vault joints, as well as butt joints for the peel plates; the central plate of the arch vault is also joined in this way. It was stated that a plate thickness of 8 mm or more requires butt joints – but under what circumstances is this necessary? Under what circumstances should lapping be used? Question 3: For the roof deck panels and rib plates, some are joined using lap joints while others use butted joints. In what situations are butted joints used, and in what situations are lap joints used? Is it clearly specified in that standard? Question 4: In what cases should the bottom plates be joined end-to-end, and in what cases should they be overlapped? Is it determined by the plate thickness? Who decides between lap joint and butt joint?
When using lap or butt joints, the requirements of the standards and specifications specified in the design must be followed. In my understanding, for small containers processed in factories, butt jointing is generally used, while lap jointing is more common for equipment processed on-site (except as required by regulations). The alignment requires relatively high precision in terms of dimensions. Additionally, for tanks with a diameter greater than 60 m and bottom plates that require internal anti-corrosion protection, butt welding is preferable. I’m hearing about the high lap joint strength for the first time.
At the construction site, the bottom plates of small tanks are mostly joined end to end, while those of large tanks are generally overlapped. Joints at the top slab have hardly been used; overlaps are what are used instead.
For the butt joints of the tank bottom plate, edge plates, and mid-span plates, are shims required at all of these butt joints?
“It is said that because of the small size of the tanks, no detailed drawings or node diagrams are created. Who said that? It fails to meet the requirements of the construction drawings, so construction is not possible!
Yes, refer to section 11.3.2.1 of the Practical Technology Series on Pressure Vessels, \"Knowledge of Pressure Vessel Design\": when joining the bottom plates of a pressure vessel, gussets are used, and single-sided butt welding is employed. On the other hand, this also serves to protect the foundation by preventing leaks at the joint from causing corrosion of the foundation
The weld is too long; even with shims in place, those shims will still contract and deform. What should be done?
It’s what the design says. I won’t take the blame for this.
Shims are generally divided into primary shims and secondary shims. Primary shims are the same length as the welds, while secondary shims are mainly used at T-joints. The length of the secondary shims is generally 100 mm in front of and behind the T-joint; this is done primarily to prevent a depression from forming at that location during welding, as well as to enhance strength. When welding with shims, the shims must be welded firmly to the weld.
The shrinkage deformation of the backing plate is mainly controlled by counter-deformation as well as welding methods and processes.
Shims have been added, with secondary shims in particular being placed beneath the tank bottom plate. Due to the presence of these shims, is there a gap between the tank bottom plate and the foundation, preventing it from resting flat on the foundation?