Purging stainless tank?

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Hi, I just welded up a stainless water tank, after I was done a worker that works at my in-laws workshop suggested I should have purged the tank when welding (fill it with gas so it has a nice finish on the inside no dags and so on) I didn’t know about this as I haven’t really done much tig welding before. The worker suggested bits could brake off inside the tank and clog things up.The water tank is 20Liters (0.9mm stainless) it just holds water in a Miniature steam loco tender, is there any chance the dags on the inside could fall off?ThanksDarren
Reply:Yes, there is always a possibility the "sugar" pieces can fall off. I've taken the quick road on some stuff and haven't seen it happen. If I can reach it, most times I just hit it with the flap wheel or stone wheel.John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Yes daz, purging out the inside gives you nice clean finish on the inside. Be sure that what is going in (CFH) is not higher than at your torch or it may create a little back pressure. On pipe you can manipulate the CFH to change the concavity/convexityof the weld. If the tank is just used to hold water you can hold a match at the end and if it blows out, you should have a good purge inside. It is the procedure that is used on probably all food and pharmaceutical grade pipe welds. I've done it on schedule 5 & 10 SS "beer welds". If you don't, you WILL get the black sugar on the inside. There is a product called Solar Flux that I've used on some less critical SS lines. It does prevent the sugar, but it doesn't leave the nicest finish either. Sorry to be long winded, just wanted to give you as much as I could for future ref.
Reply:Thanks for your replies,I have just been talking to a welder instructor I know, he is going to give me some acid to clean up the black oxidization on the inside, he said after that is done nothing else would come off from the inside.Darren