July 17 (Reuters) - BlackRock-led investors in Saudi Aramco's gas pipelines network, Greensaif Pipelines Bidco, have given initial price guidance for its U.S. dollar denominated dual-tranche amortizing bonds, fixed income news service IFR disclosed on Wednesday.

The initial price guidance for 12-year and 18-year amortizing bonds has been placed at around 205 and 225 basis points over U.S. Treasuries respectively, the IFR said. The tranches have weighted average lives of 10 and 14.5 years, respectively.

Greensaif Pipelines Bidco, the debt issuer indirectly owned by BlackRock and Hassana Investment Co, Is expected to price the debt later in the day.

The deal is reported to be benchmark-sized, which is typically understood to be at least $500 million. (Reporting by Mohammad Edrees)