Issues related to campus and non-destructive testing of composite plate tube sections
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The issues related to campus and non-destructive testing of composite plate tube sections have always been problems that pose challenges in manufacturing. Taking the Q345R+S30408(20+3) composite plate as an example (with a requirement of 100% RT inspection), we generally carry out the RT inspection after the rolling process, after welding the base layer. If no overlay is welded on the base layer, the strength of the welds and their edges is relatively low, and stress concentration occurs. In such cases, when rolling is performed and the process reaches the longitudinal seams, the rolling machine may shift, resulting in uneven stress distribution, which could damage the welds on the base layer, causing cracks or tears in them. Therefore, we usually weld the overlay before rolling and then conduct the RT inspection afterward. However, this imposes high requirements on the quality of the welds (since there are many issues with the transition layer welds themselves, though these are not related to welding problems in the base layer; yet these issues show up in the RT inspection results). Thus, I would like to discuss with everyone the issues related to rolling and non-destructive testing of composite plate sections. Let’s discuss this issue in several parts: 1) Is there a certain range (based on manufacturing experience) within which it is possible to carry out shaping without welding a cladding layer? For example, appropriate wall thickness, radius of curvature, and material quality. Outside this range, shaping must be done after welding the cladding layer first. 2) In front of the campus, it is possible to, after welding on the base layer, apply a section of clad steel plate onto the surface of those welds, in order to reduce the impact damage caused by the rolling machine during the processing of the base layer welds. 3) If the cladding is welded first and then the campus work is carried out, how should the evaluation criteria be established? 4) The approach we are using at present is as follows: RT inspection is carried out on the base layer in front of the campus, followed by welding of the overlay layer; after that, RT inspection is performed again on the welds at 100%. Other defects such as pores and inclusions are not subject to repair, while any cracks are repaired thoroughly. This approach seems relatively conservative, but it ensures manufacturing quality.
RT is performed on the base layer in front of the campus, followed by welding of the overlay layer; after that, RT is carried out again on the welds at 100%. Other defects such as pores and slag inclusions are not repaired, but if cracks are present, strict repairs are carried out. This solution is quite feasible; however, if the porosity and slag inclusions exceed the specified limits, rework will be necessary.
I basically approve of your plan. But why are defects such as pores and slag inclusions not repaired...
Actually, the reason I mentioned for not carrying out repairs on defects other than cracks is that it’s necessary. We know that welding the cladding layers, especially the transition layers, is very difficult to control and tends to result in many defects. If we use the radiographic tests taken after welding the cladding layers to determine which areas need repair, the amount that requires correction would be too large. For RT radiographs, we provide those of the base layer; generally speaking, there are no issues from a strength perspective. The radiographs taken after welding the cladding layers are used only for our internal quality control purposes, not as archival records, so the requirements can be relaxed accordingly. As for crack defects, due to their propagative nature, they require repair, while other defects are simply ignored.
Then why conduct another RT test? Just use the direct PT surface, right?
Then why conduct another RT test? Just use the direct PT surface, right? ---------------------------------------------------------------------------- RT is performed mainly to check for cracks in the transition layer, while surface coating PT is certainly carried out, but it cannot detect defects inside, especially cracks in the transition layer.
I think the second method you mentioned could be tried. Before rounding, a carbon steel strip with the same thickness as the cladding is spot-welded on the inner side of the longitudinal seam where the cladding has been removed. Once rounding is successful, the steel strip is removed, and the spot-weld marks are polished away; thereafter, RT testing is conducted on the longitudinal seam of the base material. After the RT test yields satisfactory results, the longitudinal seam is clad, and UT and PT tests are performed to check the quality of the cladding. This should be more efficient.
I think the second method you mentioned could be tried. Before rounding, a carbon steel strip with the same thickness as the cladding is spot-welded on the inner side of the longitudinal seam where the cladding has been removed. Once rounding is successful, the steel strip is removed, and the spot-weld marks are polished away; thereafter, RT testing is conducted on the longitudinal seam of the base material. After the RT test yields satisfactory results, the longitudinal seam is clad, and UT and PT tests are performed to check the quality of the cladding. This should be more efficient. ---------------------------------------------------------------------------------------------------------- I agree with you; it would be a good approach and worth trying. In fact, during straightening, since the area of the weld seam is basically flat, it is necessary to use rollers to roll over that area repeatedly. In the case of composite plates, the seam is located at the center of the rolling process, and combined with the welding stresses, the stress conditions in this seam become very complex; as a result, the seam can easily be damaged during the straightening process. When the radius of curvature is small, the base layer is thick, or the hardenability of the base layer material is high, it will have an adverse effect on the longitudinal seams of the base layer during straightening.
In the manufacturing of pressure vessels belonging to the composite plate category, it is necessary to ensure both the corrosion resistance of the composite layer and the pressure resistance of the base layer; if the strength of the composite layer is taken into account in the design, then its strength and quality must also be considered. In the actual manufacturing process, the process department should break down and understand the requirements of the designer; the manufacturer then produces the product in accordance with those requirements. The welding of the layers can be carried out simultaneously after welding the base layer, with joint inspection being performed at the same time, unless welding is not possible (such as in the case of titanium composite plate containers). Because if there are internal cracks in the layers of a composite panel, once the equipment is in use those cracks can spread to the base layer, leaving no guarantee of safety. Only by welding and inspecting simultaneously, and welding the base layer and the overlay together, can the overall safety and reliability of the equipment be ensured. Surface inspection of composite layers is also an essential requirement, as specified in the standards.