* Letter to PG&E asks for top 100 high priority projects
* Asks for estimated costs of replacing manual valves
SAN FRANCISCO, Sept 18 (Reuters) - California utility regulators asked Pacific Gas & Electric Co to provide a list of potential weak spots in the company's natural gas network, a week after a gas pipeline explosion in a San Francisco suburb killed four people.
In a letter to PG&E on Friday, the California Public Utilities Commission's executive director asked the utility to provide a list of its top 100 high-priority projects to upgrade or replace portions of the pipeline for reasons of public safety.
CPUC spokeswoman Terrie Prosper said that PG&E, whose parent company is PG&E Corp (PCG.N), had referred to such a list in a filing, but has not submitted the actual document.
The commission asked PG&E for the status of all proposed projects on the list, a map showing the location of each pipeline segment on the list and details of the criteria used to determine which projects are classified as high priority.
The CPUC has appointed an independent panel of experts to help its investigation of the explosion on Sept. 9 in San Bruno that destroyed 37 homes and injured more than 50 people. The blast was caused by a ruptured section of its natural gas pipeline that was installed around 1956.
The letter to PG&E also asks for a list of locations on the gas transmission system in which manual valves could be replaced by remotely operated or automatic valves, and an estimate of the cost of such replacement valves.
PG&E has a network that includes 42,141 miles (67,815 km) of natural gas distribution pipeline and 6,438 miles (10,360 km) of transmission, or high pressure, pipeline, serving 4.3 million customers. (Reporting by Alexei Oreskovic)