The safety of the two Mackinac Straits oil pipes is becoming an issue. I was a member of the team that welded up those two four-mile-long pipes and dragged them across the straits back in 1953. At that time we were told that the pipes would last for 50 years. Well, that was more than 61 years ago.
Why worry? Design specifications called for a minimum bend radius of no less than 1,700 feet and unsupported spans of no more than 75 feet. The bottom is hilly; to meet these specifications dredging was required. Fifteen-foot-wide trenches were cut through the tops of the hills, but deep-water dredging was not an exact science using technology of the 1950s.
What about the bending stress in the pipes, added to the stress from the oil pressure, roughly 400 psi? The roughly 1,500 welded joints shouldn’t be an issue. Each joint was X-rayed twice.
Has external corrosion reduced the strength of the pipes? Before being filled with oil, the pipes were filled with water and pressurized to 1,200 psi for 10 hours.
Perhaps they should be filled with water and pressure checked again today.