The White Sox shored up their catching depth significantly Friday, signing 30-year-old free agent Welington Castillo to a two-year, $15 million contract with a club option for a third season.

The move figures to improve the Sox on the defensive side behind the plate while adding pop to the lineup. General manager Rick Hahn was surprised that he was able to acquire Castillo.

“I don’t think I would have told you a month ago we were going to wind up signing Welington Castillo to a two-year deal with a club option,’’ Hahn said. “But ultimately that opportunity arose, and we felt it improved us for the short term and potentially for the long, so we moved quickly on it.’’

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The right-handed-hitting Castillo threw out a baseball-best 44 percent of basestealers, improved his pitch framing and batted .282/.323/.490 with 20 home runs in 365 plate appearances for the Orioles in 2017. He declined a $7 million option from the O’s and will receive $7.25 million in both 2018 and 2019 with a $8 million club option for 2020 with a $500,000 buyout.

Left-handed hitter Omar Narvaez and right-handed hitter -Kevan Smith, who shared catching duties last season for the Sox, drop behind Castillo on the depth chart.

“He’s very sound at controlling the running game,’’ Hahn said. “He’s a solid blocker, and we’ve seen improvements over the last couple of years in terms of his framing, which Welington has made a priority for himself.’’

Castillo is eager to be reunited with manager Rick Renteria, for whom he played with the Cubs in 2014.

“It’s great to be working with [Renteria] again,’’ Castillo said. “He’s a great human being and great manager.

“I’m going to do everything I know to do to help this team win and help him win, too.’’

Castillo is a career .259 hitter with 80 home runs and 283 RBI in 605 games over eight major-league seasons with the Cubs, Mariners (2015), Diamondbacks (2015-16) and Orioles (2017). Renteria made a push for the Sox to reel him in.

“Ricky spoke very highly of him and was a big advocate in favor of this move and adding not only what Welington brings between the lines from a production standpoint, but also the impact we feel he’ll have in a positive way on our clubhouse and on our young players,’’ said Hahn, who tried signing Castillo last offseason.

NOTES: The Sox agreed to terms on a one-year, $1.05 million contract with right-hander Danny Farquhar and declined to tender contracts to three other right-handed relievers — Al Alburquerque, Jake Petricka and Zach Putnam — and infielder Alen Hanson.

• Right-hander Rob Scahill signed a minor-league deal with an invitation to spring training.

• Hahn characterized the Sox’ chances of signing two-way Japanese phenom Shohei Ohtani as a “long shot,” but a presentation was submitted to the free-agent pitcher/slugger.

The Sox are capped at an offer of $300,000 because they exceeded their signing-bonus pool in the previous collective-bargaining agreement.

Follow me on Twitter @CST_soxvan.

Email: dvanschouwen@suntimes.com