The new MEPC.159(55) effluent standards that apply to all sewage treatment systems installed after January 1, 2010, will make the already challenging job of cleaning up our global water supply even tougher. Choosing the most appropriate marine and offshore industrial water and wastewater disinfection system is, of course, an important consideration when seeking to meet these new standards. But the selection of the proper piping system to keep the disinfection systems operational also is key.
In business for nearly 30 years, Severn Trent De Nora has had the opportunity to put a variety of piping materials to the test. The company is recognized for its innovative approach to water treatment utilizing on-site generated sodium hypochlorite produced from seawater. Its novel OMNIPURE™ system is the only marine sewage treatment system that oxidizes sewage in an electrochemical cell, as well as generates sodium hypochlorite for the disinfection of sewage streams. And Severn Trent De Nora’s BALPURE® system provides an effective and economical solution for treating ballast water.
Marine vessels and offshore structures must take into account the weight of products that are installed on board. Plastic pipe is one-sixth to one-eighth the weight of comparably sized metal pipe in larger-dimension systems typically installed in many marine and offshore applications. Heavier materials create not only economic problems, but also logistical challenges.
Another benefit of using plastic pipe in offshore applications is that it is easy to cut and join on site. As a result, the need for a certified welder is eliminated. “With plastic, our customers are off line for minutes to complete routine maintenance or repairs instead of days,” said Dana Casbeer, marine and offshore product manager for Severn Trent De Nora.
According to Casbeer, the company has evaluated PVC, GRP fiberglass and lined metallic plumbing. “But increasingly, CPVC (chlorinated polyvinyl chloride) pipe and fittings are being used to ensure corrosion resistance and durability not found in metallic systems. And we’ve found that Corzan CPVC delivers the most consistent, trouble-free performance in demanding environments.
“Corrosion is a serious threat in all marine and offshore applications,” said
Casbeer. “Our equipment is working in a saline atmosphere and pumping
raw sewage, seawater and sodium hypochlorite at pressures up to 150 psi in
some cases. All of these are highly corrosive, especially given the high levels
of chloride found in salt water. Compounding these challenges is the fact that
our customers are typically out at sea, far from the material and labor resources
needed to repair or re-pipe traditional metallic systems. Downtime is expensive,
and it can put our customers at risk of incurring fines for not being in compliance
with effluent discharge regulations.”
Abrasion resistance is a critical factor, too, because seawater has a high degree of particulates that can rub against the interior of the pipe. This creates an elevated concern for ships or platforms located in shallow water, where it is common to process silt from the bottom of the seafloor, shale fragments and even marine life with shells.
Temperature also is a major factor considering that a large percentage of offshore platforms are located in areas where it’s not uncommon for the ambient air temperature to go above 110°F (43°C). An important consideration is that PVC is not pressure rated above 140°F (60°C). Although the ambient air and operating temperatures might not typically rise to this limit, sunlight’s radiant effects should also be considered. Recent ASTM D4803-97-compliant testing proved that radiant heat from the sun can increase pipe surface temperatures in excess of 50°F (10°C). So, when temperatures are close to 95°F (35°C), the effects of radiant heat buildup could easily push the pipe surface temperature beyond the 140°F (60°C) pressure rating for PVC. Since Corzan CPVC pipe is pressure rated up to 200°F (93°C), it can still safely be used (even considering radiant heat buildup) in extreme cases of 120°F+ (49°C+) outdoor conditions.
“We have to meet the strictest requirements set forth by the American Bureau of Shipping (ABS), as well as a host of other certifying agencies,” said Rudy Matousek, manager of technology for Severn Trent De Nora. “It is these agencies that often require materials that exhibit additional properties, such as the higher temperature and pressure rating provided by Corzan pipe and fittings.”
According to Casbeer, Corzan CPVC is used for some of Severn Trent De Nora’s largest and most visible water treatment installations, including the OMNIPURE system currently in operation on British Petroleum’s Thunder Horse oil and gas field. Located approximately 150 miles southeast of New Orleans, it is the largest offshore installation of its kind in the world. The Thunder Horse’s OMNIPURE system, installed in 2005, has been performing reliably without problems or downtime thanks, in part, to the reliability of the Corzan CPVC piping system.
For more information, e-mail info@severntrentservices.com.