Pittsburgh-based L.B. Foster Co. announced Monday it has reached an agreement to acquire Chemtec Energy Services LLC, a major supplier of blending, injection and custody transfer metering skids for use in the oil and gas industry. Chemtec, which is based in Willis, Texas, will expand L.B. Foster's (Nasdaq: FSTER) presence in the midstream market, according to the company. "The addition of Chemtec Energy Services to L.B. Foster's expanding energy group offers new markets within our existing customer…