Questions regarding the welding process evaluation of heat exchange tubes and tube sheets
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This post was last edited by Border on 2019-2-15 at 14:19. Product welding conditions: 1. The tube and the tube sheet are joined using a strong weld; a groove is made in the tube sheet. 2. Both the tube and the tube sheet are made of S30408 material; the tube has a diameter of φ25×2mm, and the tube sheet has a thickness of 70mm. 3. Automatic TIG welding is used to join the tube and the tube sheet. Question: Is it necessary to conduct process qualification using two sets of plates with different thicknesses, one for each of the tube and tube sheet thicknesses? If so, to cover the tube sheet thickness, should a plate with a thickness of 40 mm be used, welded by TIG welding?
This post was last edited by kangyusai on 2019-2-15 at 14:38. 1. It is definitely necessary to conduct a weldability assessment using two plates of different thicknesses in order to cover the cases where the tube and the tube sheet have different thicknesses. 2. Thin plate butt joints can be welded using pure TIG welding. 3. For thick plate butt joints, TIG welding + manual welding can be used. The combined process qualification can be used separately; the base metal coverage thickness and the combined qualification coverage thickness are equal, but the weld coverage thickness is twice the thickness of the welds produced by the individual welding methods in the process qualification test plates. If the weld thickness for TIG welding in your process evaluation is 3 mm, and the maximum cover thickness for the base material is 200 mm, then the maximum cover thickness for the weld is 2×3=6 mm.
This post was last edited by Border on 2019-2-15 at 16:34. When using combined welding methods for thick plate evaluation, is TIG welding used for the root pass, with manual welding being used for the remaining layers? Are there any particular requirements regarding the welding method in sequence? Are there any specific requirements for the sampling locations of the mechanical properties of test specimens? I would be very grateful for a reply.
Our approach is to conduct additional assessments of the heat exchange tubes and tube sheets in accordance with Appendix D of NB/T47014-2011, and to add an assessment of the butt welds of the sheet metal in order to meet the requirements for the welded components (as long as it covers the thickness of the weld metal). Because the welding of the heat exchange tubes to the tube sheet is not a fully penetrative structure.
TIG welding for the root pass, manual welding for the finish pass. For sampling and the like, follow the standards; there are no special requirements.
At first, we did the same, but later the inspection team said that Appendix D contained a corrigendum, stating that it was only suitable for situations where expansion welding is used in combination
This post was last edited by Border on 2019-2-16 at 16:36
This correction does exist. In my opinion, gasket expansion is intended to eliminate the gap between the heat exchange tubes and the inner walls of the tube sheet holes, thereby reducing gap corrosion; it has little to do with the strength of the connection between the heat exchange tubes and the tube sheet. There are no corresponding regulations for pure strength welding, so the additional assessment in Appendix D of NB/T47014-2011 can be referred to.
Only talk about the issue of strength. Refer to Article 4 of Table 9 in NB/T 47014: equal-thickness test pieces are used to evaluate products with unequal thickness. In your case, simply weld a 6mm-thick S30408 plate into a butt joint test piece, and that will suffice.
This post was last edited by wanlirn on 2019-2-23 at 12:53. Just one fitting is sufficient; the pipes and the tube sheet are connected by fillet welds, and even when bevels are used, it remains a fillet weld. Ge Zhaowen – Standard Q&A
Brother Ge’s view is still too general; each case needs to be analyzed on its own. 1) In the case of high-intensity welding, the requirements regarding the root gap height differ significantly depending on whether a groove is made on the tube sheet or not. What is nominally called a chamfer is, in actual welding, a grooved weld, and such grooved welds must comply with the evaluation criteria for butt welds. Because 47014 is essentially just a translation of ASME Volume 9, with it having been reorganized and summarized according to our local reading habits. Volume 9 of ASME defines the concept of groove welding. 2) If the weld serves only a sealing function, that is, in the so-called strength expansion + sealing weld connection method, it is then appropriate to talk about chamfering rather than beveling; in this case, the welding process can be determined based on the criteria for fillet welds.