A question regarding the tube sheet and shell
Thread Content
I have a question I’d like to ask. Regarding the welds between the carbon steel heat exchange tube sheet and the shell – for example, if the tube sheet is 16MN grade and has a thickness of over 40 mm, while the shell is made of Q345R with a thickness of 16 mm – as shown in the diagram, is it necessary to preheat the thick side of the tube sheet? 1.47015 and GB150 define preheating in terms of the thickness of the weld metal; according to these standards, preheating is intended to reduce the constraints resulting from repeated heating and cooling during welding. The smaller the thickness, the lesser the degree of such constraint. From this, it can be understood that preheating is not required. 2. If preheating is required, for WPS, it is necessary to enter a preheating temperature of over 80°C. A question that arises for me is: regarding weld evaluation for 40 mm thick materials (covering ranges from 16 to 200), how do people handle the preheating step? The materials left by seniors in the past were not preheated, which resulted in a wider coverage (assuming that this case does not require preheating). If preheating was applied for the weld evaluation, to cover this row, preheating should be entered. . . . It’s a bit complicated; please take a look
This is the forum post regarding preheating for weld evaluation, https://bbs.hcbbs.com/thread-748259-1-1.html
Does it need preheating at just 16mm? What is the reason?
Thank you for your reply. I considered this from that perspective: this structure involves the butt joint of thick and thin plates, so either a weld assessment for Q345R thick plates is required, or additional thin plates need to be used for coverage. There is a recommendation to preheat when the thick plate welding evaluation is greater than 28 mm. Therefore, I am focusing on the content in the **bolded portion**.
Look at the purpose and application point of the weld!
If the main welding test plates are fine, then preheating is not necessary
Thank you! Is it feasible to use 40mm test plates without preheating, as long as the physical and chemical test results are satisfactory?
No preheating is required; NB/T47014 does not stipulate that preheating is necessary, so why go to the trouble of doing it?； If preheating is used, it must be ensured that the difference between the workpiece temperature and the preheating temperature specified for the evaluation is less than 50 degrees.