StifPipe® Test Results

The standard test for determining stiffness of liners is provided by ASTM D2412-02 “Standard Test Method for Determination of External Loading Characteristics of Plastic Pipe by Parallel-Plate Loading”. The figure on the right shows the set up for such tests at the Department of Mining and Geological Engineering, The University of Arizona.

To demonstrate the advantages of this system for a recent project, our technicians constructed two nominally 36-inch diameter pipe sections specifically for the project as shown to he right. The pipe in the front was made of 6-layers of VU18C carbon fabric, exactly the same design as was required for this project; the average pipe liner thickness was 0.30 inches. The StifPipe® shown in the back was made of a layer of our honeycomb core confined between a layer of QuakeWrap VB26G glass fabric on either side. This liner had an average thickness of 0.71 inches. We intentionally used one layer of glass on the inside of the pipe (instead of two layers of carbon fabric) to be conservative.

The results for both pipe liners are presented here. As can be seen, the StifPipe® has a stiffness that is 2.1 times that of the conventional CFRP system with 6 layers of carbon fabric.

The actual StifPipe® for this project will include a single layer of glass or carbon on the outside but on the inside, we will use two layers of VU18C carbon fabric to meet the design requirements for resisting the internal pressure of the pipe. This will even increase the stiffness of the StifPipe® further.

The new StifPipe® system has numerous advantages over the conventional CFRP liner, including higher strength and stiffness, superior quality, ability to test the actual pipe sections before installation, and shorter shutdown time. The only disadvantage of StifPipe® is that it will reduce the pipe diameter by a slight amount over the CFRP system. However, considering all the other significant attributes, it is clear that StifPipe® is the preferred method for repair of most pressurized pipes.