You may be new to DuroMaxx® Steel Reinforced Polyethylene (SRPE for short) pipe. If you are, here is a brief introduction. What is DuroMaxx SRPE? DuroMaxx is the brand name for this innovative technology. “Durability / Maximum Benefits / Ultra Large” … if you get the naming methodology. And steel reinforced polyethylene is exactly what it sounds like. It is a polyethylene (PE) pipe barrel that is reinforced structurally by steel rib members. Currently, it is manufactured in diameters of 30-inch up to ultra-large diameters of 120-inch. That is impressive.
First thing to note, DuroMaxx pipe is considered a flexible pipe type that has a “profile wall”. Profile walled thermoplastics have been around for a long time. However, with the incorporation of steel, it is no longer a traditional flexible thermoplastic pipe. Instead, it acts like a steel or metal flexible pipe when buried. There are many advantages on this topic that I can cover in another blog!
The photo below shows the steel ribs encapsulated completely in polyethylene.
The steel is 80 ksi galvanized steel. The PE pipe barrel is HDB pressure-rated resin. The same resin you get with the well-known solid wall PE pipe used in pressure applications. Most solid wall PE pipe has thick wall sections. This is primarily to address pressure and pipe burst resistance. If you are designing for a gravity or low-pressure head application, a thicker wall section is not necessary, due to lower pressure requirements. What you do need is strength – structural strength for direct bury applications under gravity flow.
Reminder, PE has an elastic modulus of 110,000 psi, but steel has an elastic modulus of 29,000,00 psi. The steel reinforcing ribs allow us to reduce the wall thickness of DuroMaxx dramatically. The thickness of DuroMaxx was determined for several reasons: handling loads, hydraulic loads, abrasion resistance, pressures etc. Just know, the steel is doing all the structural work … the PE is along for the ride to provide abrasion and chemical resistance, among other things.
Wall Thickness and Abrasion
DuroMaxx’s wall thickness was designed using industry standard abrasion rates. PE has a far superior abrasion resistance than other materials in the industry, such as reinforced concrete pipe (RCP). DuroMaxx’s wall thickness abrasion rate meets or exceeds the abrasion rate of RCP’s steel exposure under the same common abrasion conditions.
Structural Design and Specifications
DuroMaxx meets all requirements of ASTM F2562 (Published 2007) for use in non-pressure drainage, storm sewer and sanitary sewer applications. The design methodology that has been used to establish the structural performance limits for DuroMaxx has been tested for over a decade and proven appropriate and conservative. The steel reinforcing ribs in the DuroMaxx profile react to loads in a manner like corrugated metal pipe. The design methodology used with DuroMaxx utilizes the current AASHTO LRFD design methodology for corrugated metal pipe with one additional check to account for the potential of local buckling within the steel rib profile. AASHTO Bridge Subcommittee approved a revision to include steel reinforced polyethylene (SRPE) in the revision of LRFD Bridge Specifications for Metal Design & Metal Construction. Currently, SRPE is included in AASHTO M335 and MP-40 for all diameters up to 120 inches.
What You Get
SRPE is innovative in many ways. The unique combination of durable PE with the well-known strength of steel allows the production of a highly efficient profiled walled pipe in ultra-large diameter sets. The manufacturing process also plays a large part in the pipe’s success across the US. The inherent qualities of the materials being used and the profile design itself lend to a very fast manufacturing rate as compared to other materials. The efficient profile wall provides much lighter material weights, longer joining sections and, therefore, faster installation rates as compared to commonly used materials in large diameter applications. This all leads to a highly cost competitive solution for those looking for another quality material in 36-inch and larger sanitary, storm sewer, reline and underground storage solutions.
At the end of the day, there is a significant amount of information documenting that steel reinforced polyethylene (PE) is a highly competitive solution for sewer applications commonly specified fiberglass or concrete. Because the PE material and the steel reinforcement play key roles in the long-term performance of DuroMaxx® pipe, it is important to understand that this is not your typical thermoplastic pipe material. It is much more.