Metal processing firm Reliance Steel & Aluminum Co. of downtown Los Angeles announced Monday that Chief Executive David Hannah will step down in May as part of a succession plan. He will be replaced by President and Chief Operating Officer Gregg Mollins.

Hannah, 63, has served as Reliance’s chief executive since 1999 and as chairman since 2007. He will step down May 20 but continue as executive chairman until July, 2016.

Mollins, 60, is a 29-year veteran with Reliance and was named chief operating officer in 1994. He has also served as president since 2002 and as a board member since 1997.

Reliance shares closed Monday at $57.42, up 0.7 percent.