Type of S. County Pipe Called Corrosion-Prone

The 20-year-old water main that exploded in south Orange County, forcing officials to ask 700,000 residents to practice drought-like conservation for the next week, includes concrete pipe that Southern California water officials have stopped using after a string of costly ruptures.

Officials at the Metropolitan Water District found that the “prestressed” concrete pipe is prone to corrosion and was blamed for a devastating pipeline rupture in the Mojave Desert that disrupted water flow to Southern California in the mid-1980s.

In fact, the district recently replaced 1,000 feet of pipeline near the San Diego Freeway, on the Orange County-Los Angeles County border, after finding cracks and other damage inside the pipeline.

Officials on Tuesday probed a variety of possible causes for the South County rupture, including a recent earthquake and defective construction. But a prime focus is corrosion, which occurs when moisture attacks the concrete and the steel cables embedded within.

Similar pipelines by a variety of manufacturers have failed in the past, with more than 40 ruptures occurring worldwide since 1950, according to a 1992 federal lawsuit filed in Arizona. In previous instances, the steel cable that wrapped around the concrete pipe weakened and eventually snapped.

“We’re only in the preliminary part of this investigation,” said Jill Wicke, the MWD’s water systems manager. “We are in the process of looking at whether or not it was corrosion or if there was some other cause.”

Inspectors found that four 20-foot segments of the water main were damaged by the rupture, which blew out a 10-foot hole and cracked a joint between two pipe segments, Wicke said.

The pipe, buried 25 feet underground, exploded with such force that concrete fragments knifed to the surface and flew through the air. Officials compared the rupture to the explosion of a large bomb.

“This is not a particular design that we would use in future pipelines,” Wicke said.

The damaged segments will be replaced by steel pipe segments from the water district’s manufacturing plant in La Verne, and the water main is expected to be up and running by Monday, Wicke said.

About 20% of the Metropolitan Water District’s 750-mile pipeline system is made from prestressed concrete, which is encased in a steel cylinder and tightly wrapped with steel wire. The MWD now drains and inspects the inside of every concrete pipeline in its network on a five-year cycle. The pipeline that ruptured in South County was last inspected in 1996 and received a clean bill of heath, said Eddie Rigdon, assistant water system manager.

MWD officials said they first became concerned about possible corrosion after a state Department of Water Resources pipe exploded in the Mojave Desert about 15 years ago, Rigdon said. More recent ruptures have been reported in Arizona, Florida and other states.

“That [Mojave] rupture caused us to look very hard at our pipelines,” said Rigdon.

Inspectors discovered evidence of corrosion two years ago in a feeder line that runs from a Yorba Linda filtration station to Palos Verdes. About 1,000 feet of pipe was replaced, Rigdon said.

The Municipal Water District of Orange County, the wholesale water supplier for the area, built the pipeline in 1981--a time when prestressed concrete was still commonly used. The district sold it to the regional water authority in 1996.

“This is something you wouldn’t expect in a pipeline this young,” said Keith G. Coolidge, associate general manager of the Municipal Water District.

But the president of the company that manufactured the pipe disputed the characterization, describing the concrete line as “middle-aged.”

“It’s up there,” said Tom Giese, president of Ameron Concrete and Steel Pipe Group in Rancho Cucamonga, a subsidiary of Pasadena-based Ameron International Inc. “It’s quite a lengthy service period.”

The company sent out a field representative to inspect the damage and help authorities investigate the cause of the rupture. Giese said it’s too early to tell whether an earthquake weakened the pipe. Most siphons are built to withstand temblors, he said, using rubber gaskets at the joints to allow the pipes to move during a quake.

Ameron is one of world’s leading makers of large piping and other materials for the industrial, chemical, oil and construction markets.

Giese said he could not immediately recall any recent ruptures of the company’s pipes locally since he arrived in Southern California seven years ago.

In 1991, a large Ameron pipe running from San Mateo County to San Francisco ruptured.

Around the same time, federal engineers working on an Arizona aqueduct said they discovered that corrosion on a giant Ameron water pipe had eaten into steel wire wrapping several sections together.

The Central Arizona Water Conservation District filed suit against Ameron and other firms. The suit, however, was dismissed by a judge in 1994.

* CONSERVATION THE KEY

As officials worked to keep water flowing, residents took the request to conserve in stride. B1