Do a web search for a Material Safety Data Sheet for sulfur hexafluoride. You can also get trnasportation requirements off of the U.S.A. Department of Transportation.
Shipping SF6 itself should not be any more difficult than transporting propane, compressed oxygen, liquid nitrogen, acetylene, or any refrigerant.
What I would do with SF6 equipment is to get a refrigerant recovery machine plus a refrigerant recycling machine plus recovered refrigerant storage tanks. I would then pump most of the SF6 into the recovery tank. The refrigerant recycling unit will allow you to remove any moisture and other foreign substances. Your equipment is less likely to leak if the SF6 pressure inside is only a few pounds per square inch gauge and the rest of the SF6 is in the recovery storage tank. All other things being equal, SF6 storage tanks will be more rugged than the equipment.
SF6 electrical equipment is inherently more rugged and earthquakeproof than oil filled. However, you also need to consult the manufacturer as to proper lifting techniques regardless of whether you use a forklift truck or a crane. The wrong rigging **WILL** crack the tank.
I am also taking the same philosophy as when transporting oil filled electrical equipment. Transporting any kind of machine that has oil in it will stir up sediment even if you drain out the oil. At least when you drain out the oil you can filter it and scoop sludge off the bottom of the transformer or circuit breaker tank. Also, most tanks for large oil transformers that are NOT pad mounted are not strong enough to be transported with oil inside. With large oil filled transformers there is the matter that when filled with oil they are just too doggone heavy.
I think that the geographic area of interest is Romania, judging after the initiator's name. Unfortunately, the SF6 technology is not very developed over there, and the equipment using SF6 is imported. What can I say about this topic is that you have to consult first the manufacturer's manuals and shipping instructions in order to handle the equipment correctly. Special problems may occur during transportation, due to road restrictions or difficulties (i.e. bridges that have a limited load allowance, or clearences with respect to overcrossing bridges or HV lines, etc.), but these can be solutioned co-operating with the local agencies specialized in roads and bridges operation and maintenance. The guys will tell you how to choose the best route to your location.
