Authored by: Steve Ferry, Microbac Laboratories, Inc., Hauser Division

Some time ago, the Florida Department of Transportation (FDOT) embarked on an ambitious program to install corrugated polyethylene (PE) land drainage piping with 100-year design service life in the state of Florida. These types of PE land drainage products are typically covered by the ASTM F2306 Standard Specification for 12 to 60 in. [300 to 1500 mm] Annular Corrugated Profile-Wall Polyethylene (PE) Pipe and Fittings for Gravity-Flow Storm Sewer and Subsurface Drainage Applications, AASHTO M294 Standard Specification for Corrugated Polyethylene Pipe, 300- to 1500-mm Diameter, or AASHTO M252  Standard Specification for Corrugated Polyethylene Drainage Pipe product specifications. FDOT partnered with Dr. Grace Hsuan of Drexel University, Dr. Timothy McGrath of Simpson Gumpertz & Heger Inc., and manufacturers of corrugated PE pipe, from which a suite of test methods and product specification requirements were promulgated. These test methods and product specifications are now embodied within the State of Florida Standard Specifications for Road and Bridge Construction, Section 948 Drainage Materials, Miscellaneous Types of Pipe as Class II corrugated PE pipe (Obtained from the Florida Department of Transportation website on 11/18/2008; http://www.dot.state.fl.us/specificationsoffice/Implemented/CurrentBK/CurrentSpecs/948.pdf).

The general suite of requirements starts with the AASHTO M294 materials requirements with added requirements for oxidation and slow crack growth resistance. Typical PE resins would be classified in accordance with ASTM D3350 as 335400C materials, with short term oxidative induction time (OIT) requirements of 25 minutes when tested in accordance with ASTM D3895 Standard Test Method for Oxidative-Induction Time of Polyolefins by Differential Scanning Calorimetry, and greater than 24 hour failure times when tested in accordance with ASTM F2136 Standard Test Method for Notched, Constant Ligament-Stress (NCLS) Test to Determine Slow-Crack-Growth Resistance of HDPE Resins or HDPE Corrugated Pipe. Additionally, FDOT then requires the material and product to meet Florida Methods of Test FM5-572, FM5-574, FM5-575, and FM 5-577. These test methods and requirements are described in further detail below.

FM 5-572: This test methodology consists of three individual test procedures A, B, and C:

Procedure A covers testing of the as-manufactured pipe liner for stress crack resistance. A minimum of five (5) individual ASTM F2136 test specimens are removed from the pipe sample in a helical sampling pattern at approximately even intervals down the length of a stick of pipe and tested at 50°C using a 10% Igepal solution. The average failure time of the five (5) test specimens must exceed 17 hours, and no single failure time shall be less than 12 hours.

Procedure B covers testing of the as-manufactured junction, connecting the pipe liner and pipe corrugation for stress crack resistance. A minimum of five (5) individual ASTM D638 Standard Test Method for Tensile Properties of Plastics Type IV test specimens are removed from the pipe sample in a helical sampling pattern at approximately even intervals down the length of a stick of pipe and tested at the three test conditions of 80°C /650 psi, 80°C /450 psi, and 70°C /650 psi. The total (average) testing time must exceed 110 hours at the 80°C /650 psi test conditions, 430 hours at the 80°C /450 psi test conditions, and 500 hours at the 70°C /650 psi test conditions.

Procedure C covers testing of the as-manufactured longitudinal profiles (such as mold lines or vents) for stress crack resistance in a manner similar to Procedure B, although these are circumferential (hoop) direction test specimens. A minimum of five (5) individual ASTM D638 Type IV test specimens (representing each type of regularly-occurring longitudinal artifact) are removed from the pipe sample at approximately even intervals down the length of a stick of pipe and tested at the three test conditions of 80°C /650 psi, 80°C /450 psi, and 70°C /650 psi with time duration requirements identical to the Procedure B requirements.

Note that all FM5-572 Procedure A, B, and C testing is performed via creep-rupture testing mode with constant stress monitoring for time-to-failure of the test specimens, although the product specification requirements allow for stopping of testing and removal of test specimens after the required testing time has been exceeded. Also note that for a typical large diameter product, whereby the leading and trailing junctions do not fit within the reduced section of the ASTM D638 Type IV specimen, and containing mold lines at two diametrically-located positions and vents also at two diametrically-located positions, a total of 95 specimens must be tested (5 Procedure A, 30 Procedure B, and 60 Procedure C).

FM 5-574: This test methodology consists of two individual test procedures A and B, although Procedure B is typically not performed due to the long time duration and cost. Procedure A is described in further detail below:

Procedure A (Single Point Test) covers testing of the as-manufactured pipe liner for oxidation resistance. A minimum of five (5) individual ASTM D638 Type IV test specimens (note that these are identical to the FM5-572 Procedure B specimens) are removed from the pipe sample and exposed at 85°C in a water bath with the specimens stressed at 250 psi for 136 days. After this “incubation” duplicate ASTM D3895 test specimens are removed from the area of the specimen which was stressed to 250 psi. The average OIT test results must exceed three (3) minutes, and no single value shall be below two (2) minutes. Additionally, the Melt Index of two of the three ASTM D638 Type IV specimens is determined in accordance with ASTM D1238 Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer, the results of which must be within 80% to 120% of the starting “exemplar” material.

The results of the above-described Florida DOT FM5-572 and FM5-574 testing are then evaluated, and if minimum requirements have been exceeded, an “interim” approval is granted by Florida DOT.

The manufacturer is then required to continue with testing, specifically the Florida Method of Test for Determining Creep Rupture of Corrugated Pipe Liner Tensile Specimens Designation FM5-575 and Florida Method of Test for Predicting Long-Term Flexural Modulus of HDPE Corrugated Pipes Designation FM5-577.

Successful completion of this extensive testing protocol should allow for the successful use of corrugated HDPE pipe for time durations rarely exhibited by materials and products currently used in our infrastructure.

Microbac Laboratories, Inc., Hauser Division is the only laboratory in the world which maintains ISO 17025 Accreditation for these Florida DOT and embedded ASTM test methods.

For more information, please contact: microbac_info@microbac.com.