I can't answer you, not having any experience with cryogenic piping. I have to wonder, though, what would happen when liquid gas at minus 150 (CO2 ?) is exposed to the heat from welding. I'm guessing that you would have a violent reaction if the liquid vaporizes rapidly.
CHGuilford
I have never tried this, and would not recommend that it is done without some serious trials. None the less, I will give some opinions, but don't quote me!
You mentioned hot cracking. I believe that this should be no bigger problem at low temperatures than normal ambient temperatures because it is related to inter-dendritic cracking due to the presence of low melting point constituents. A faster freezing should reduce the tendancy of the lower melting point constituents to migrate to the grain boundaries. This means that fast freezing should help reduce hot cracking rather than increase the problem. At any rate, you would want to ensure a totally clean welding surface before starting your weld.
I would be worried about the vibration, depending on how much it is. A pipe support expert may be able to recommend a set-up that may reduce the vibration during welding.
I do not think that the fast cooling would have detrimental effects on the 304L base material. This is based on the fact that austenitic S/Steels are typically quench annealed to ensure sound properties are achieved. (Here the material is heated to approx. 1000°C and water quenched.) In addition, austenitic S/Steels are typically very ductile even down to temperatures much lower than your's.
There was a concern raised regarding the vapourisation of the cryogenic liquid during welding. (Is it a liquid?) This concern will be very much a function of the thickness of the material. A thicker material would almost certainly not become very hot on the inside of the pipe, due to the cooling effect of the fluid flowing past the inside of the pipe, cooling it down rapidly.
The big problem that I would have with this exercise is the typical issue with all "hot welding". (Cold welding in your case:-) Can the pipe contain the pressure while it is heated to a high temperature? There are typically guidelines in the API codes that gives guidance here. If I am not mistaken, it is not recommended to weld on pipes thinner than 5mm in thickness.
Another issue would be to ensure that your hot tapping tool is compatible with the low temperatures and the fluid in question.
At the end of the day, any such exercise is a matter of assessing the risks involved. If you are welding on a pipe conveying a very hazardous fluid, (ammonia?) then the risk obviously increases. Only your team can assess all the hazards, because you have all the information.
Hope this helps
Regards
Niekie Jooste
Jim:
Good points made here. While in the Middle East, hot tap parameters were very narrow and the applications were even more limited. The temperature envelope really limited where hot-tapping could be performed. Niekie's remark regarding the tool used to make the tap can perform at that temp. is a good one, that was my first thought. Don't forget that many materials begin to lose their mechanical properties as temperatures go to extremes (hot or cold). I've witnessed lots of hot taps, but never at this temp. (not even close to your temp.)
I also share the opinion that hot-cracking will not be an issue. [By the way, when hot-tapping the weld is not made with product coming in contact in the weld area, unless something has gone wrong.]
My other concern would be the temperature differentials in the same vicinity of the service line.
I really hope you let us all know how you resolve this one. Often people post problems, we try to help and we never here from them again. Kind of like the "reverse mcavana syndrome".
What about a tap using mechanical attachments i.e.: bolted/clamps?
Wow, 150F below, that's cold.
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