Do the high-strength steel welds welded to the gusset plates on the outside of the housing require heat treatment?
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Our factory has a pressure vessel whose main material is high-strength steel, 18MnMoNbR, with a thickness of over 100 mm. In the original design, the external supports were also made of 18MnMoNbR and were welded directly to the vessel shell, using full-thickness fillet welds that were 50 mm thick. The equipment undergoes segmented heat treatment. To ensure the accuracy of the supports, the design drawings were modified; a 10-mm-thick Q345R steel plate was added as a shimming plate at the locations where the supports would be installed on the outside of the housing. (Due to the tight deadline, 18MnMoNbR was not available and difficult to obtain, so the readily available Q345R was used instead.) The supports were welded to the shimming plates based on the actual connection dimensions, which led to some problems: First, is it reasonable to use Q345R for the shimming plates? Is it allowed? Secondly, isn’t it pointless to use Q345R for the shims and 18MnMoNbR for the supports? Third, can the fillet weld between the shell 18MnMoNbR and the gasket plate Q345R be evaluated using 18MnMoNbR as a reference? (The welding materials and process remain the same, using 18MnMoNbR.) ) Fourth, after adding the gusset plate, the support is welded to the plate; so this fillet weld doesn’t require heat treatment, right? If heat treatment is not carried out as per the standards, will there be any problems in actual use? (The equipment is quite heavy, over 300 tons, and the supports have to bear significant forces.) Since some of the fillet welds from the segmented heat treatment can be included during the heat treatment of the second segment, is it necessary to include them in the heat treatment process?
First, Q345R can be used for the gusset plates, but weldability tests must be conducted on the fillet welds connecting them to the shell; only welding processes that pass these tests may be employed；
Secondly, using Q345R for the shims is sufficient; it makes no sense to use 18MnMoNbR for the supports, as their role is to support the equipment；
Third, cannot the fillet welds between the shell 18MnMoNbR and the gasket plate Q345R be evaluated using 18MnMoNbR for coverage? This was already explained in point one；
Fourth, after adding the gusset plate, the support is welded to the plate, so this fillet weld does not require heat treatment.
Q345 is sufficient for the supports; there’s no need to use 18MnMoNbR anymore, as it’s unnecessary.
First, is it reasonable to use Q345R for the shims? Is it allowed? In my opinion, it is best for the shims to be made of the same material as the cylinder. If Q345R is used for the shims, then it makes no sense to use 18MnMoNbR for the supports. Secondly, isn’t it pointless to use Q345R for the shims and 18MnMoNbR for the supports? Third, can the fillet weld between the shell 18MnMoNbR and the gasket plate Q345R be evaluated using 18MnMoNbR as a reference? (The welding materials and process remain the same, using 18MnMoNbR.) ) With important factors such as welding materials and processes remaining unchanged, 18MnMoNbR can be used for assessment. Fourthly, after adding a gusset plate, the support is welded to this plate; in that case, isn’t heat treatment required for this fillet weld? In my opinion, strict enforcement is necessary, and heat treatment should also be carried out to prevent the formation of cracks
This post was last edited by HanShanJieShui on January 4, 2016, at 10:55. (First, is it reasonable to use Q345R for the backing plate?) Is it allowed? ): It’s clearly a design modification, so there’s no need to worry too much about it. They must have done the calculations; logically, the strength level of Q345 is about 10 kgf/mm2 lower than that of 18MnMoNbR. I’m not an expert in design, so I won’t comment further. I’m puzzled regarding both the thickness and material of the shims – the material should be the same as before, and so should the thickness. I remember that the thickness difference resulting from this modification is quite significant; maybe I just didn’t fully understand what you meant. (Secondly, is it pointless to use Q345R for the shims and 18MnMoNbR for the supports?) ): Generally speaking, it indeed makes no sense to do that; I’m not sure why the design wasn’t modified accordingly. Anyway, I recall that the standards for supports don’t require the support material to be the same as that of the cylinder – only the gasket material is specified. (Third, can the fillet weld between the shell 18MnMoNbR and the gasket plate Q345R be evaluated using 18MnMoNbR as a reference?) (The welding materials and process remain the same, using 18MnMoNbR.) ））: It can cover that; I assume the standard used for welding assessment by you is also NB47014, so refer to clause 6.1.2.1 – no problem. (Fourth, after adding the gusset plate, the support is welded to the plate; so this fillet weld doesn’t require heat treatment, right?) If heat treatment is not carried out as per the standards, will there be any problems in actual use? (The equipment is quite heavy, over 300 tons, and the supports have to bear significant forces.) Since some of the fillet welds from the segmented heat treatment can be included during the heat treatment of the second segment, is it necessary to include them in the heat treatment process? ): My understanding is that, following the principle of more stringent heat treatment practices, heat treatment should be carried out in accordance with the specifications for 18MnMoNbR.
Answering the first two questions from a design perspective: First, is it reasonable to use Q345R for the shims? Is it allowed? It’s generally not designed this way. In principle, the base plate should be made of the same material as the equipment itself. This is mainly because the welds that are formed by direct welding to the stressed components of the equipment belong to Class E welds, and they are relatively important compared to ordinary structural welds. If the gasket material is the same as that of the main body, there is no need to select a different welding material or conduct another process evaluation. Furthermore, for a device as heavy as 300T, whether it has ear mounts, saddle mounts, or skirt mounts, the wall thickness of the structure forming its body should be considerable, at least greater than 10 mm. If the gasket is only 10 mm thick, it is difficult to ensure the leg thickness of the fillet weld between the gasket and the support plate, which can lead to the failure of the support. It is recommended to increase the thickness of the shimming plate to at least the same as that of the support. Secondly, isn’t it pointless to use Q345R for the shims and 18MnMoNbR for the supports? Yes. The purpose of using shims is to avoid using the same pressure vessel material as that of the equipment itself for the supports, thereby saving costs. However, since the support material has been changed from high-strength steel to Q345R, it is necessary to ask the designer to conduct recalculation.
First, is it reasonable to use Q345R for the shims? Is it allowed? In principle, the material of the shimming plate should be the same as that of the equipment itself. This is mainly because the welds that are directly welded to the pressure-bearing parts of the equipment are crucial, as they can directly affect the stress distribution in the cylinder. Secondly, isn’t it pointless to use Q345R for the shims and 18MnMoNbR for the supports? Sure it is. Since the shims are made of Q345R, the material for the supports can be either Q345R or Q345; however, it is essential to have the designer conduct a calculation.
It should be covered according to NBT47014.