A member of another fly fishing board set up to test the strength of the DIY welded fly line loops that has been circulating on many of the fly fishing boards on the internet. Here are his results:

He set up and suspended a 5 gallon bucket from a fly line with a welded loop with several trials. He filled the bucket with water until the line broke and then weighed the bucket. He got several results, not particularly good--15.4 lbs, 13.7 lbs and 7.8 lbs. Considering that most fly lines are thought to have a strength of 30 Lbs, that translates to 51%, 46% and 26% strength in the welded loops compared to a fly lines strength. What he noticed, was that it broke in all three cases in the weld region with the doubled line. Further, the line was a bit discolored in the region of the break. He used a heat gun to shrink the heat-shrink tubing and do the weld, and he guessed he got it too hot indicated by the discoloration. That lowest value 7.8 lbs was the most discolored. So he went back and tried to make a weld that was not discolored. It wasn't easy but he finally got one that seemed worth testing, no visible discoloration and got 19.7 lbs, again breaking in the weld region. Then by way of comparison, he tested a braided loop connection of the type favored by Dan Blanton and others and got 26.7 lbs., and it did not break anywhere near the connection. So his conclusion is that this is an elegant but unfortunately too unreliable a method to put a loop in a line.