Saudi Aramco and US firm ConocoPhillips have again extended the deadline for bids for a solids handling unit at their Yanbu refinery joint venture, industry sources said on Saturday.

The deadline is now June 1 for bids on the construction of the unit at the 400,000 barrels per day (bpd) refinery, two sources close to the bidding process said. The companies were not immediately reachable for comment.

Italy's Saipem, Argentina's Techint, Britain's Petrofac, South Africa's Senet, ThyssenKrupp Robins, Flsmidth and South Korea's Daelim Industrial Company are bidding for the solids handling unit package, sources said.

The bidding's closing date, originally February 28, had been pushed to March 22. The engineering, procurement and construction (EPC) tender is split into 11 packages.

US firm KBR completed the front-end engineering and design (FEED) of the refinery. "The extension of the bidding closing date is due to additional work requested by the client," one source told Reuters.

The extension will give contractors more time to prepare proposals for the extra work or "addendum 1" tender which will be issued on April 20, the source said.

A second source said the extension was due to design modifications. Aramco and Conoco are now evaluating bids for five other EPC contracts that include a coking unit, a crude facility, a gasoline unit, a hydrocracker and a tank farm, sources familiar with the matter said.

Both companies have started clarification meetings with contractors, they said. All EPC contracts are expected to be awarded in May. Saudi Arabia plans to double total domestic and international refining capacity by 2015.-Reuters