Think thats about right, W sizes cost £80 a yr rental and about £45 a bottle plus vat. See if there is an air products agent new you and check AP's prices rental will be about the same but the gas might be a little cheaper. Bear in mind BOC and AP charge a handling fee every time you change the bottle which is about £12.
So if you are not going to be a high volume user, you are better off with BOC, and X size cylinder gives around 250 minutes worth of welding at 10 ltrs per min, on smaller torches you can get away with less.
Must admit the other day for some unknow reason i had turn the gas right down and it was running at about 4ltrs per min and that was on a mb25 torch, no noticeable bad welds, but would have not liked to cut into the weld as it would most likely be porus as hell.
Just thought i would quickly point out, that the large bottles aren't that much more expensive AP's bottle rental seems to be almost the same and not size dependant, where as BOC bottle rental is cheaper for smaller bottles, but the gas costs more in preportion
X size is 2.42m3 or 2420 ltrs Y size is 5.02m3 or 5020ltrs and W size is 11.71m3 or 1171ltrs
Yes, it seems to work out that low volume use (say one X per year) is cheaper with BOC, but higher use is cheaper with AP as their gas is so much cheaper and their rental stays the same for bigger bottles.
To be honest neither BOC or AP are not that interested in the DIY section of the market, its not really worth there hassle, one bottle a year etc. The majority of there market lies with fabricators like me and bigger who rent 4 + bottles a year and end up spending £1500 a year plus with them.
not really sure on that taitsie, never got on that well with the AP website, its to busy trying to promote the company rather than the products it sells. Logic would say an x30 would be a 3mtr3 bottle and an X47 would be a 4.7mtr3 bottle but having looked at there website logic isnt something that they use