The mainline Ruy Lopez usually avoids trade offs for quite awhile.
Just for curiosity...
http://www.xs4all.nl/~timkr/records/records.htm
31 moves.
Nuber - Keckeisen
Mengen 1994
..for a decisive game.
Two others made it to move 70+ and were draws.
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What has been the longest game between masters without any capture?
What openings allow you to keep mostly all the pieces over the board an search for complications?