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Jul. 14, 2007

ASTM Testing for Cured in Place Thermosetting Pipe

Author: Douglas Bert

One of the most common products in the pipeline rehabilitation industry today is cured in place thermosetting pipe (CIPP).  CIPP is a trenchless technique in which a new liner is formed inside an existing pipeline to repair pitting, internal corrosion, erosion and general degradation to the pipeline.  In this process a tube impregnated with a thermosetting resin is inserted into the host pipe and then expanded and cured to form a tight fitting pipe within a pipe.

This technique is applicable to many types of pipe from sewer mainlines and laterals, industrial and special waste pipeline to pressure pipe.  The type of resin used in the process is determined by the application in which the pipe will be used.  The generic types of resin are polyester (sewer pipe), vinyl ester (industrial and special waste pipe) and epoxy (potable water and pressure pipe).

The installation of CIPP is performed either by inversion or pull in place. Inversion is a process in which the lining tube turns inside out and travels down the pipeline using a pressurized system of water, steam or compressed air. The pull in place method uses a winch to install the collapsed lining tube and then inflates the liner using compressed air.  In both installation techniques the liner is cured using hot water or steam.

Both the product specification for CIPP (ASTM D5813) and the installation procedures (ASTM F1216 and F1743) contain testing protocols for the purpose of quality assurance. These protocols are in place to give the installer a starting point for the design process, as well as to provide the end buyer a way to determine if the product was designed and installed properly.

The purpose of this article is to provide both installers and buyers a guide to the CIPP industry testing.   This article will also provide a basic idea of what testing is appropriate for the product in question.

1. Short-Term Properties:

Flexural Properties (ASTM D790): This is the most common test performed on post-installed CIPP samples. In this procedure, a bar of the CIPP material is placed across a span, the length of which is usually 16 times the thickness of the specimen. The specimen is then loaded at a constant rate at its midpoint. Both the deflection and the force are measured throughout the test. In order to prepare specimens which conform to the ASTM D790 requirements, a minimum axial sample length of 20 times the thickness is required.

Tensile Properties (ASTM D638): In this procedure tensile specimens are cut in the shape of a “dog bone” with two wider tabs on each side of a central reduced section. The reduced section concentrates stress in this dimensionally controlled area. The specimen is then pulled in tension at a controlled rate and the maximum force is recorded to give the tensile strength. Additionally, the tensile modulus is measured using an extensometer.

Delamination (ASTM D903): This test only applies to multi-layer installations. In this test, only half of the test coupon is wetted out and cured. The remainder of the coupon consists of dry felt. The testing consists of separating the two cured felt layers by pulling on the dry portions of the two layers of felt.

Thickness Measurement (ASTM D3567 / D5813, Section 8.12): This is simply eight measurements around the circumference of the pipe taken with calipers, micrometers, or an optical gage. These measurements must include both a minimum and maximum wall thickness excluding any seams, fins, or other non-representative locations. These measurements should also exclude any nonstructural layers such as polyurethane or polyethylene tube coatings.

2. Long-Term Properties:

Chemical Resistance (ASTM D543/ ASTM F1216 / ASTM D1538 / ASTM F1743 / L.A. Green Book Pickle Jar):  These tests compare physical properties (usually flexural properties, but can also include tensile properties, weight change, and hardness change) between specimens that have been exposed to a given chemical and like specimens that have not been exposed. For CIPP, these exposures can last from one month to one year.

Flexural Creep (ASTM D2990): This test setup is very similar to the short-term flexural properties test ASTM D790. The specimen is placed across a span (usually 16 times the thickness of the specimen) and loaded at the midpoint of the span. In this test a constant load is used rather than a constant rate of loading.  The deflection of the specimen is then measured multiple times over a given time span (usually 10,000 hours for CIPP). The data obtained from this is then extrapolated out to fifty years to predict how the CIPP will perform over this period of time.

Strain Corrosion (ASTM D3681): This test was originally designed for the fiberglass pipe industry but has become a common CIPP test.  In this test, a section of the pipe is compressed to induce a specific strain, the specimen is held in this deflected position and both sides are dammed off. An acid solution is added to the dammed off pipe section and a time to failure is recorded (or simply evaluated pass/fail depending on the product specification).

3. Additional Testing:

These tests are not required in the CIPP product and installation specifications, but they provide valuable information about the CIPP product.

Izod Impact Resistance (ASTM D256): A short bar of the sample has a notch cut into one side. The bar is then placed vertically in a vise and a pendulum impacts the notched side of the bar. The energy that is lost from the pendulum to the bar is measured, and the impact resistance is derived from that reading.

Compressive Properties (ASTM D695): A small prism of the sample is compressed in a universal testing machine. Loading force is usually the only needed measurement, but deflection can also be measured for those interested in compressive strains and compressive modulus.

Punch Shear (ASTM D732): A plate of the sample is held rigidly between two steel plates. A one inch diameter circular section of the material is punched through the center of the sample. Shear strength is the ultimate force recorded during this test divided by the surface area of the sheared area.

Density (ASTM D792 or ASTM D1622): Density is measured by water displacement as in ASTM D792 or by simply dividing the mass of a sample by its volume as in ASTM D1622.

Parallel Plate Loading (ASTM D2412): A section of pipe is loaded on its side and compressed to a given deflection determined from the pipe’s dimensions. The force at this deflection is then used to calculate a stiffness factor.

Barcol Hardness (ASTM D2583) or Rockwell Hardness (ASTM D785): Barcol hardness is a measurement of the distance an indenter (dull needle) can be pressed into the surface of the material in question with a set pressure applied to the indenter. Rockwell hardness is similar, but the difference in penetration distance between two pressures is measured instead of just the one.

Resin Infrared Spectroscopy: A baseline resin IR spectrum is compared to an IR spectrum of a resin sample taken onsite after the CIPP process has occurred.  This testing ensures that the product installed is the same as the product tendered.

This article presented a basic overview and description of the various testing methods used in the quality assurance system designed for CIPP.

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