Lincoln has some good methodoligies. If you can get your hands on their Welding Pressure Pipelines & Piping Systems booklet, it will givey ou some good guidance. I'm sute there are other resoiurces available on the Internet.
Basically, it's a volume calculation depending on your joint geometry & fit up - how much volume of rod/consumable goes into each weld and what does it weigh.
For remote, cross country pipelines, generally what we will do is calcualte the theoretical amount of electrodes (in lbs or kgs) and order 50% more.
Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website: