Norton Co., based in Worcester, Mass., which owns one half of Eastman Christensen Co., says it will buy the remaining 50 percent partnership interest in the Salt Lake City company for $115 million from its joint-venture partner Texas Eastern Corp.

Closing of the purchase is subject to certain agreements and government-mandated waiting periods.Martin R. Reid, chief executive officer of Eastman Christensen, said he was pleased Norton decided to become sole owner. "Norton is a well run, strategically managed company and can be expected to fully support Eastman Christensen's continued growth," said Reid.

Eastman Christensen employs 275 at three Salt Lake locations. The firm's 1988 income before tax was $23 million on revenues of $221 million. Norton has 1,650 employees worldwide with 46 facilities in 20 countries.

Eastman Christensen is a supplier of petroleum drilling products and services. The company was formed in 1986 as a partnership jointly owned by Norton and Texas Eastern. The partnership combined oil service companies Norton Christensen and Eastman Whipstock.