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For 40-foot joints of schedule 40 pipe, multiply the nominal pipe diameter by 22.5; the answer is pounds of electrode per mile of pipe line.
Example: 6-inch pipe; 6 * 2.5 = 135 pounds per mile.
Example: 10-inch pipe, 30-foot joints; 10 * 22.5 = 225 pounds per mile, for 40-foot joints; 225 * (40/30) = 300 pounds per mile for 30-foot joints.
The rule is based on standard weight (schedule 40) pipe, and the usual number of passes, which varies from two for small pipe up to four for 16 inches; larger pipe is usually thinner wall; the rule includes an allowance for wastage.