i used to weld tanks ,aircraft ,boats,all of them some with water ,some with argon .i have had two of them do flame outs not blow but left the table like a jet airplane .after the second one i said screw this there to unpredictable .and for what money was involved was not worth it so i stopped well my dad kept on doing them and i would tell him its only a matter of time pops before you pop one and sure enough boom 40gallon alum take blew, the end cap blew of the tank sheared the regulator of the argon bottle bounced of some walls and stuck half way though our office wall blew all the light bulbs out of the shop and the windows blew the steel end caps off our steel building and sent the tank out the big door about 150 feet,it broke my dads nose ,hand and he cant hear with out hearing aids now .he was lucky that the end cap and baffle blew off in one shot.i wasn't there at the time but was called about it right after, it looked like a bomb went off and with all the blood in the shop i just knew i had just lost my dad.the explosion was so big that it shook brick buildings down the street.and to make matters worst it was 1 day after the Oklahoma bombing we had every state and federal task force there is at our place wanting to know what we did there lol.after going over everything on why it blew we came to the conclusion he made a mistake when you purge with argon its hi volume in and low out there were many vents in tank so he plugged them with duct tape we have done this many times before with no probs but this time when making the the argon vent hole he used a awl to poke threw the tape and when pulled the awl back out the tape re closed .and wallah no vent struck arc and boom .so those that weld tanks and think theres no threat at all don't forget your still human and your day will come no matter how good you think you are .so ask your self is the money really worth it .