Motiva Enterprises, a joint venture between Royal Dutch Shell and Saudi Aramco, has rescheduled a planned overhaul of a 200,000-barrel-per-day crude distillation unit at its Port Arthur, Texas, refinery until 2015.

This is the second time the work has been delayed, sources familiar with refinery operations said.

Motiva also plans to shut the 90,000-bpd gasoline-producing fluidic catalytic cracking (FCC) unit at Port Arthur for a second time in 2014 to repair a leaking boiler, said the sources.

The company has also scheduled a planned overhaul of a hydrotreater at the 600,000-bpd Port Arthur refinery for July, the sources said.

A Motiva spokeswoman declined to discuss maintenance plans for Port Arthur, the nation's largest refinery.

The planned overhaul of the 200,000 bpd VPS-4 crude distillation unit had been originally scheduled for February.

However, it was rescheduled late last year for autumn 2014 with a likely September start after two reviews found fault with the refinery's readiness to carry out an complete overhaul of a major unit.

The FCC was to be shut for a full overhaul at the same time as VPS-4, which supplies gasoil for the FCC to convert into unfinished gasoline.

Because of the reviews, the refinery is not expected to be ready for the giant overhaul of VPS-4 and the FCC until the fall of 2015, the sources said.

The refinery's managers are also concerned about the availability of contractors who can perform the work. At least 1,000 workers will be needed to work on VPS-4 alone, the sources said.

While VPS-4 is shut, the refinery's other two crude distillation units (CDU), which have a combined refining capacity of 400,000 bpd are scheduled to remain in operation.

The leaking FCC boiler led to a shutdown of the FCC for about two weeks at the beginning of this year.

The boiler provides steam used to prevent the release of catalyst from the FCC into the atmosphere, as required by environmental regulations.

The moisture from steam helps capture the fine powder catalyst from being released through an exhaust stack. If steam production fails, the FCC has to be shut until steam can be restored.

The FCC will be shut later this year when the leaking boiler again fails to produce enough steam to capture the catalyst, the sources said.

That shutdown could come in the early spring, so as to avoid the period of highest demand for gasoline in the late spring and summer months.

Only repairs on the boiler are planned for this year, not a full FCC overhaul, the sources said.

The hydrotreater work has been on refinery's schedule for sometime, the sources said.

A hydrotreater uses hydrogen to remove sulfur from gasoline in compliance with environmental regulations. A CDU does the primary refining of crude oil coming into a refinery and supplies feedstock for all other production units.-Reuters