Elliot,
When I was a welder, I was just a very averege one :) so you might want to take the post with a grain of salt.
As the other guy mention its important to feather you tacks - and each stop - before futher welding.
I dont know if you use a remore control to adjust your amps, if you do you might want to give it a little extra just as you come to the point where you stopped before. Once you get used to stick welding on pipes, you can actually hear when you have penetration.
I have never welded with cellulose coated electrodes myself, but I think I have heard something about the angle, distance, etc. is a little different than with 7018. It might be a good idea to master one technique before moving on to another.
I welded from: 3- 12, 6 - 12 and then 6 - 3 to avoid distortion.
3.2