Corrosive, aggressive soil had eaten through a 35 year old ductile iron pipeline in the Port of Tampa area, causing a multitude of leaks that could not be repaired. Replacing the rotten pipe with more iron would have been costly and shortsighted. The radical environment required polyvinyl chloride (PVC) piping.
For Tampa water department engineers, an internal joint restraint that eliminated the need for external fixtures on PVC pipe fittings was a promising solution for the problem. Careful research and deliberations led staff to a unanimous decision to use the progressive technology.
Engineers believe the conditions that so easily destroyed the iron water main expected to last 100 years may be typical of many American ports. In Tampa, contamination came from soil dredged from the bay, which likely contained residual chlorides-a deadly enemy of ductile iron pipe. It is also possible that the groundwater in the area suffers from salt-water intrusion. More than 13 unstoppable leaks were found in a 200 ft section of the old iron water main.
The Tampa Water Department approved the purchase of 960 feet of PVC piping with an internal joint restraint system, which was used in a project that began in November 2009 and concluded in January 2010.
Contractor Approval
Installation of the PVC piping was the responsibility of Dallas 1 Construction & Development. The contractor specializes in underground utilities, including storm drains, sanitary systems and roadwork. With 28 years of experience working with pipe ranging in size from 2 to 84 in, the contractor was familiar with local city and county needs. Steve Mitchell, production pipe foreman, says the port project was the first time they had encountered an innovative internal joint restraint system.
"Once I read the instructions, away we went," Mitchell said. "After installing a few we thought, this is great, much easier than ductile iron. I like the lock system because you do not have to physically install a locking system or put a restraint on the pipe itself. This system saves time because the lock is already installed. I have been doing this for 35 years, and I think it would work well in any number of situations."
According to Mitchell, the timesaving aspect of the internal restraint joint was particularly helpful because digging in the port area was difficult. The combination of toxic soil and rotted ductile slowed the process considerably. The Dallas 1 Construction crew could lay more pipe per day than would have been expected with ductile or other products that require old-fashioned restraints.
"One particular day we laid 640 ft of pipe. If I used restraint joints, we probably would have gotten only 450 to 500 ft installed because it takes about 30 minutes per restraint. Not only do you put them on, you have to get into the hole and put the bolts through. On the 12 in pipe, which is what we were installing, usually you need two bolts per side of the joint, and then you have to snug them up."
Saving time was not the only virtue of using PVC. The lightweight, indestructible piping meant Mitchell's crew did not have to expend as much physical energy to complete the job. Therefore, they were more productive each day.
"It saves energy and physical abuse to the body. We do a lot of deep, nasty big pipe, so we are used to a lot of loading and locking up of pipe. Using this product is different. There are virtually no man-hours needed for the restraints. Personally, I think the system is fantastic, and every one of the guys who worked the project said they liked it too."
Cities See Future in PVC
Before the port project, the largest PVC installed by the Tampa Water Department was 8 in diameter. Why was it slow to adapt to other PVC products?
According to local industry expert Roy Thames, president and CEO of Thames and Associates, Tampa is "similar to many municipalities, where engineers embrace new standards and products only after the technology has been thoroughly tested and proven. In this case, ductile iron had been the reigning standard material for many years." Engineers were ready to rethink their approach after digging up the rotting ductile iron.
Mitchell concurred. "It is not that Tampa officials do not like PVC. Like many municipalities, the city is picky about trying new products. The corrosive soil gave them no choice. This port island was pumped in 50 years ago. They did not have a lot of regulations, so everything you can imagine probably got put in there. Every iron pipe we have dug up has been totally eaten."
Soil corrosion was not the only problem engineers needed PVC products to overcome. Another sensitive issue for Tampa officials was the many live loads that the water pipe would endure on a daily basis.
The intersection of Gatx Drive and Guy N Verger Boulevard, where PVC pipe was installed, leads to one of many docks in the Tampa Port Authority district. Large trailer trucks traverse the area at all hours of the day. Understandably, city engineers initially expressed concern about PVC's ability to handle the pressure and weight. Conclusive evidence of PVC's suitability for the project came from an Army Corps of Engineers study.
"There is not a person who puts pipe in the ground who would not like this product," says Mitchell. "As long as you follow the manufacturer's guidelines, you will not have any problems."
The internal joint restraint also solved another dilemma that allowed Tampa to avoid a costly renovation. The port water main crosses underneath railroad tracks in three locations. Replacement pipes, plastic or iron, would need to fit through existing protective underground sleeves. Engineers knew that external restraints would typically make the replacement pipe too big to fit. Since using ductile iron was not an option, and expanding the underground sleeves would cost time and labor, Tampa personnel were in a bind until the internal joint restraint system.
PVC Benefits in Any Economy
Internal joint restraint technology is fitted into the bell portion of PVC pipe when it is manufactured. During on-site installation, each set of connected pipe immediately locks as the joints are put together. To promote corrosion resistance, the internal joint restraint is encased within the PVC pipe, so it is never exposed to soil and flowing fluids.
Installation of iron typically creates complications-and man-hour demands-not associated with the use of plastic pipe. For example, Mitchell calculated that the use of plastic pipe with internal joint restraint on the Port of Tampa job saved him a few days of labor.
Other costs include making a separate run to pick up restraint and joint fixtures for ductile pipe. The product is stored in the open air for long durations, perhaps rusting while it waits to be installed. Compare that scenario, says Mitchell, to internal joint restraint technology. When the PVC is delivered, it is ready to go.
Great savings, convenience and durability await municipal officers who realize it is time to embrace new concepts and technologies.
Diagram of internal joint restraint technology for PVC piping.
Pumps and Systems, June 2010