According to Wikipedia, the 1970s was a decade of economic upheaval, increasing political awareness and the continued liberation of women. It was also a time when below-specification PCCP pipelines were manufactured, an issue which leaves the United States in particular facing massive repair and reinforcement projects 40 years on.
PCCP (prestressed concrete cylinder pipe) was first invented in 1942. It combined the compressive strength of concrete and the tensile strength of steel to create pipelines capable of carrying huge capacities under high pressure buried underground.
The appeal of PCCP was obvious, especially for water and wastewater networks. Pipes could be constructed that were over 3.5 metres in diameter, running beneath towns, roads and countryside to provide or take away vast quantities of water.
At the heart of PCCP were pre-stressing steel wires. These were located between the concrete core of the pipe and an outer shell made from mortar, designed to protect the wires from corrosion.
The wires produced a uniform compressive pressure in the concrete core of the pipe, offsetting tensile stresses. The concrete core represented the main structural load-bearing components with a steel cylinder placed in-between two layers of concrete to act as a water barrier.
When PCCP was first introduced, it was governed by standards set by the American Water Works Association (AWWA) and a high factor of safety was used.
The composite technology used in PCCP was so new that engineers played it conservatively, knowing that if their calculations about the lifespan of PCCP were to be incorrect, then there could be serious issues when it came to repair and reinforcement down the line.
For the first 20 years, that safety factor remained in place. By the time the 1970s arrived, things began to change thanks to a mix of overconfidence in PCCP and supposed improvements in the strength of steel.
As is so often the case when it comes poor decision making, money was a factor. PCCP networks across North America were operating successfully, and that gave manufacturers the confidence to start altering the structure of PCCP in a bid to reduce the cost of production.
One of the ways they did this was by changing the composition of prestressing wires in PCCP. Based on the belief that scientific advances meant the steel they were using in the 1970s was much stronger than that used in the 1940, manufactures used thinner wires and less of them.
Between 1972 and 1978, PCCP was produced featuring these reduced quantities of prestressing wires. PCCP was considered as robust and strong as steel pipes at the time and both were meant to have lifespans of 70 to 100 years.
When water companies faced a choice between installing steel pipes or PCCP on their networks, they would nearly always go for the latter due to the cheaper cost involved.
This turned out to be a catastrophic mistake. Less wires meant more stress on the pipe. When overpressure led to the mortar shell cracking, water from the soil surrounding a buried pipe was able to enter.
The thinner prestressing wires used in 1970s PCCP were brittle and more susceptible to corrosion. Once the wires broke, water could seep into other parts of the pipe and it was just a matter of time before the line suddenly and unexpectedly failed.
To say this below specification PCCP is a problem would be an understatement. According to the American Concrete Pressure Pipe Association (ACPPA), 90 of the 100 largest water utility companies in the US use prestressed concrete cylinder pipe on their networks.
Many of these pipelines have already suffered catastrophic bursts. Alarm bells started ringing as early as 1979 when part of a 13 mile PCCP line installed in Florida only a year earlier blew out.
Another explosion occurred in the same line during pressure testing in 1980 with two more failures following over the next 14 years up to 1994, despite the line operating at well below the pressure it was meant to withstand.
After the Florida incident, PCCP standards were dramatically tightened. Pipes produced post-1979 rarely break and modern PCCP now has an overall failure rate of less than four percent – the lowest of any pipe material.
Unfortunately for PCCP, the damage has long been done to its reputation with millions of miles of below-specification pipes criss-crossing the US like ticking time bombs, just waiting to go off.
What makes PCCP bursts so troublesome is the size of the pipes involved. A rupture in a high-pressure line 3.5 metres in diameter has the potential to rapidly lose millions of litres of water, severely impacting on supplies to hundreds of thousands of people.
Irvine, Southern California experienced once such incident in 1999. A PCCP main blowout on the outskirts of the city spilt 22 million litres and left approximately 700,000 residents without water for up to a week.
In response, the water utility company responsible decided to inspect 160 miles of PCCP on their network. They discovered numerous undetected minor leaks and bursts all blamed on deterioration of PCCP.
100 miles of their PCCP network was found to be below specification, requiring repair, replacement or reinforcement. The utility company put the cost at $2.5 billion over 20 to 25 years.
In Washington, the Suburban Sanitary Commission (WSSC) has 350 miles of PCCP that have been prone to exploding without warning. Since 1996, nine mains operated by the WSSC have blown apart.
A 2008 PCCP explosion released a torrent of water that led to motorists being rescued by boat and helicopter from a street in Bethedsa, north of Washington DC.
Three years later and a water main blew out doors and walls in an office park in the town of Capitol Heights, sending a highly pressurised jet of water 40 feet into the air.
The WSSC says cost of replacing sections of PCCP in the densely populated suburbs of Washington would be $2.9 billion. Instead, they have deployed noise loggers as part of a $21.2 million break detection system designed to listen out for prestressing wire snapping.
When enough noises in a section of PCCP are detected, the pipe in question can be isolated to undergo reinforcement or repair before it explodes. The WSSC say they record wires breaking on a daily basis.
Twice since 2007, the situation has been severe enough to necessitate the shutting down of a pipe. Repairs have been accelerated on another 12 sections because of the increased frequency of wire breaks.
On a national scale, repairing or replacing PCCP across the US could cost $40 billion according to a technical assessment carried out by the U.S. Environmental Protection Agency and the American Water Works Association.
Advances in pipe repair technology can help to bring that cost down. Solutions such as epoxies and composite repair wraps can be applied to reinforce pipework, creating a protective sleeve with pressure resistance of up to 30 bar.
Combine such repair methods with improved detection – as well as noise loggers, robots are also being used to inspect pipes – and you have a system that can help to identify and prevent incidents before they happen.
Another solution for reinforcing PCCP involves relining the pipe with steel or ductile iron. Whatever method is used, water companies across the US face time consuming and costly repair and reinforcement projects to make up for the mistakes of the 1970s.
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