BIRMINGHAM, Ala. (AP) _ A judge has cleared the way for millions of homeowners nationwide to join a lawsuit filed in Alabama's poorest county over leaky plastic pipes.

Rejecting claims by Shell Oil Co. and Hoechst Celanese Corp. that Greene County, about 90 miles southwest of Birmingham, was not the proper place to hear the decade-old dispute, Circuit Judge Eddie Hardaway Jr. certified the case a nationwide class action.

The ruling may be appealed, but it also could open the door to a trial or settlement negotiations in which homeowners' lawyers have said they would seek at least $7 billion.

Shell and Hoechst Celanese made materials that went into so-called PB plumbing systems. Thousands of lawsuits have been filed nationwide over the past decade claiming the systems sprang leaks when exposed to chlorine and other chemicals commonly found in tap water.

The makers deny the pipes are faulty and blame leaks on poor installation and improper use.

They have argued homeowners' claims were too diverse to handle as a class-action and have said the case would be unmanageable because of its size.

Shell attorney Dan Hyde of Houston declined comment Wednesday, saying he still had not received a copy of the decision, which Hardaway released late Friday. Other lawyers, including those representing Hoechst Celanese, did not immediately return phone calls seeking comment.

Shell makes materials used in PB pipes, most easily recognized by their gray color. Hoechst Celanese used to make components for PB fittings.

Another corporation that made materials for fittings, DuPont Co., already has agreed to a $120 million settlement approved by Hardaway earlier this year.

In his ruling, Hardaway said any PB plumbing case in which homeowners are seeking money for property damage could be consolidated with the suit filed by Greene County Commissioner Garria Spencer, courthouse workers and other residents in November.

The Greene County case was just another lawsuit until this spring, when a Texas law firm representing 80,000 people with PB plumbing claims intervened. Juries in rural Alabama have developed a national reputation for returning huge verdicts against big companies.

PB plumbing was commonly installed in mobile homes, apartments and other low-cost forms of housing in the 1970s and '80s. The pipes and fittings were a cheap alternative to traditional metal plumbing and manufacturers estimate as many as 6 million housing units contain PB pipes.

About 46 percent of the residents in Greene County, about 90 miles southwest of Birmingham, live below the poverty line.

PB fittings are no longer on the market, but PB pipes are still in use. They are most commonly fitted with metal and rubber connectors.