Ligament Efficiency for Explosive Welding

[PhilOos]

Good day,

I want to re-tube feedwater heaters by welding the the tubes to the tubesheet by means of explosive welding. In order to do that I need to check the ligament efficiency of the tubesheet. I've looked at the ASME VIII code, but to no avail. Do I need to run computer simulations to do that, or is there a way to calculate it manually?

Kind regards,



Philip Oosthuizen
Company info:
SteinMuller Engineering Services

http://www.steinmuller.co.za/

 

[rmw]

I am not going to offer you any help with respect to calculating ligament efficiency. I assume you are referring to expanding the tubes into the tubesheet via explosive expansion. Explosive welding is a term I am more familiar with used to refer to explosive welding of plugs in tubes and tubesheets. There the explosion accelerates the plug and as it picks up velocity, it does in fact weld itself to the ID of the tube or tube wall as applicable.

And, I have seen cases on thin ligaments where explosively welded plugs have caused ligament damage to adjacent tubes when measures weren't taken to have something in those tubes to absorb the energy.

With respect to the expansion if that is what you are after, it takes a certain amount of energy to expand a given thickness of tube material into a tubesheet. Whether that energy is applied slowly via mechanical means, (rolling) or less slowly via hydraulic means, or very rapidly via explosive expansion, the energy is the same.

I can't speak for all explosive expansion charges, but the ones I am familiar with have the cordite inside a latex tube if you can believe that latex driven about anything can move tube metal. But believe me it does.

I have retubed many feedwater heaters with explosive expansion including tubes up to .110 wall which takes a real bang (sorry for the pun) and calculating ligament efficiency wasn't part of the process. I have to suppose that this was done when the process was being developed and perfected.

The method most often used is to expand tubes a complete row at a time. For the rows nearest the centerline, that is a lot of charges all at once.

That reminds me. I need to look up a floppy disc that I have. It has a camera video of a whole row being blown on a tubesheet 27 inches thick, 110 tube wall, steel tubes in a LF2 forging tubesheet. I once had it as my screensaver. The force of the blast blew over the scaffolding built for access to the channel manway, but I digress.

I don't think I answered your question but I hope I helped shed some light on your topic.

rmw