Terms of the deal were not immediately available.
Tuman, a six-year veteran, opened the 2005 season as the team's starter, but gave way to rookie Heath Miller, the team's No. 1 draft pick.
Tuman still saw plenty of playing time, however, in the team's two-tight end sets and finished the season with three catches for 57 yards.
The Steelers also re-signed offensive lineman Barrett Brooks to a one-year deal worth $770,000. Brooks will only count $550,000 against the team's cap if he makes the final roster.
To free up the money for those moves and the signings of Ryan Clark (4 years, $7.1 million) and Brett Keisel (4 years, $12.1 million), the Steelers finally agreed to terms with center Jeff Hartings on a restructured deal.
Hartings, who was scheduled to earn a base salary of $4.75 million this season, will now make just under half of that this season. In exchange, the Steelers gave the two-time Pro Bowl center a one-year contract extension for about the same money next season.
With Clark signed, sealed and delivered Tuesday as the team's new free safety Chris Hope saw the writing on the wall and signed a deal with the Tennessee Titans.
In addition, the Steelers also signed first-year fullback Brandon Joe, who played at Ohio State, and claimed veteran Doug Easlick off of waivers from San Francisco. Easlick has also played for Miami and spent time with Cincinnati.