NEW YORK - U.S. refiner Sunoco Inc said on Tuesday it is examining pipes and systems at its U.S. facilities in the wake of a May fire at its 178,000-barrel-per-day Marcus Hook, Pennsylvania, refinery.

We have begun a short-term effort at all facilities to examine piping systems and identify locations of possible concern so they can be addressed immediately, Thomas Golembeski, a Sunoco spokesperson, said in a statement.

We have begun implementing a special emphasis program for high-risk systems to be sure similar structures with similar conditions do not exist at any Sunoco facilities, he added.

Sunoco will have a third party review its revised mechanical integrity and inspection practices to identify other areas for improvement, Golembeski noted.

Sunoco said that an investigation into the cause of the May 17, 2009, fire at the ethylene complex of the Marcus Hook refinery showed that a pipe failure resulted in the release of combustible ethylene unit feed gas, which caught fire.

The pipe failure was caused by external corrosion on the bottom of the pipe, it said, adding that evidence shows that localized corrosion stemmed from moisture trapped between the pipe and a loose steel sleeve on which the pipe rested.

The corrosion, which occurred over many years, was limited to the space between the sleeve and the pipe. The rest of the pipe showed no indication of corrosion, it added.

Philadelphia-based Sunoco has total refining capacity of 825,000 barrels per day. Its other refineries include the 335,000-bpd Philadelphia complex, the 145,000-bpd Eagle Point plant in New Jersey, and the 160,000-bpd Toledo, Ohio, refinery. (Reporting by Haitham Haddadin; Editing by Christian Wiessner)