State regulators have approved plans by the state’s four investor-owned natural gas companies to modernize and update their pipeline delivery systems, replacing hundreds of miles of older pipes with state-of-the-art plastic pipe.

The Washington Utilities and Transportation Commission (UTC) last year directed the companies to survey their pipeline infrastructure and propose plans to replace pipeline with “elevated risk.” As incentive for such pipeline replacement, the UTC policy permitted the gas companies to recover costs each year, rather than waiting for a future formal rate proceeding.

“Pipeline safety is an ongoing concern, and one should never be complacent,” said UTC Chairman Dave Danner. “But these plans demonstrate that Washington’s gas utilities are committed to the safety of our state’s pipeline infrastructure. Unlike many states, we have almost none of the more dangerous cast iron pipeline that has failed in other parts of the country, and utilities all have sound plans going forward to replace some plastic pipe that has shown a tendency toward minor cracking.”

The four natural gas companies are Avista, Puget Sound Energy (PSE), Cascade Natural Gas Corp. and Northwest Natural Gas Co. The utilities serve about 1.2 million natural gas customers in Washington.

In their plans, the companies identified the pipe targeted for replacement and described how the company assessed risk and established its replacement priorities. The plans also included a schedule for determining the location of elevated-risk pipe. The plans must be updated every two years.

• Avista’s system has some older polyethylene pipe installed prior to the 1970s. Over the next two years, Avista will replace 60 miles of pipe in unincorporated Spokane County. The company has already completed replacement of plastic pipe in Davenport and Odessa.

The Spokane-based company has about 3,400 miles of natural gas pipeline in the state, and serves some 150,000 natural gas customers, primarily in Eastern Washington.

• PSE also has some older polyethylene pipe in its service territory, 400 miles of which it will upgrade over the next 20 years. In the next two years, it will upgrade 60 miles of pipe located in scattered areas from Marysville to Olympia.

In addition, the company will replace the last remaining18 miles of bare steel pipe. The company has already replaced some 200 miles of such pipe in Seattle and Tacoma over the last decade.

PSE’s miles of natural-gas distribution system in Washington includes more than 12,000 miles of pipeline. The Bellevue-based company supplies natural gas to 783,659 customers in King, Kittitas, Lewis, Pierce, Snohomish and Thurston counties.

• Cascade Natural Gas will replace 62 miles of bare steel pipeline in Longview, Shelton and Anacortes, a third of it by 2015. The Kennewick-based company has almost 4,500 miles of natural gas pipelines in its distribution network in the state.

The company serves almost 200,000 customers in 65 communities throughout the state, including Bellingham, Bremerton, Mount Vernon, Aberdeen, Longview, Moses Lake, Kennewick, Walla Walla, Wenatchee and Yakima.

• Northwest Natural Gas has scheduled all bare steel pipe to be replaced by the end of next year. The Portland-based company has about 1,700 miles of natural gas pipeline in Washington, serving about 72,000 residential and commercial customers in Clark, Skamania and Klickitat counties.

Currently, each gas company regulated by the commission recovers costs through periodic general rate cases, which can take up to 11 months. The commission created a special cost-recovery mechanism for the gas companies to replace high-risk pipe while allowing a faster recovery of the investment in new pipe in customer rates.

In 2011, the federal government adopted a new program that required natural gas distribution companies to develop procedures to ensure the safety and reliability of the pipeline delivery system. The new regulations require operators to identify those conditions, characteristics or threats that cause leaks in order to make their systems more reliable and safe.

Established by the Legislature in 1955, the UTC’s Pipeline Safety Program regulates the safety practices of 31 pipeline companies and conducts safety inspections on more than 24,000 miles of natural gas and hazardous-liquid pipelines in Washington.