Seven years before a natural-gas pipeline explosion in San Bruno killed eight people, Pacific Gas and Electric Co. engineers were alerted that a crucial piece of information about the pipe’s troubled history was missing, a newly uncovered document shows.

That information could have been tracked down at a PG&E district office in San Carlos — and if it had, the disaster might have been averted. But there is no indication PG&E sought out the information or did anything with it....

If a line has a history of failed seams — the eventual cause of the San Bruno explosion — federal law requires that it be checked with a method that can detect such a problem, such as pumping it full of water at high pressure.

That’s expensive, however, and PG&E preferred a cheaper method — one that could detect problems such as corrosion, but not a bad seam.