Gas Industry Tests

During the period July 2010 through May 2011 the strength of PipeMedic™ for repair of steel pipes carrying natural gas was tested. These tests were conducted by the Gas Technology Institute (GTI).

The pipe diameters for the three tests were 6, 12, and 16 inches. In all cases a two- or three-layered PipeMedic™ carbon or glass laminate was used to bridge a 24-inch long gap or opening in the steel pipe; the gap was intended to represent an abandoned drip pot or a T-connection that was no longer needed.

The comprehensive test report is available in pdf format at this link. The Executive Summary of the test and a link to the full report are presented below:

Executive Summary:

Hydrostatic pressure tests were performed on pipe sections with PipeMedic™ Fiber-Reinforced Polymer (FRP) composites. The test sections consisted of steel pipes of 6, 12, and 16 inches in diameter and had 24-inch free-span length of the PipeMedic composites. Cured-In-Place (CIP) liners were installed inside the pipes and the pipe sections were tested under stepped hydrostatic pressures.

The hydrostatic pressure was increased every 2 hours in 50 psig increments up to 250 psig and the liner-composite sections could stand the applied pressure without leakage.

The requirements for the CIP-pipe system as specified in the ASTM F-2207 standard include performing tests at pressures not less than twice the certified MAOP of the pipeline for a minimum of one hour without leakage. For gas mains operating at pressures up to 60 psig, the hydrostatic tests exceeded the above requirement and showed that the composite sections could withstand pressures up to four times the operating pressure without leakage.

The strains of the PipeMedic™ sections were monitored using strain gauges. Strain measurements in the two types of PipeMedic™ composites in the testing program were as follows:
‐ In the 16-inch pipe, three layers of the PipeMedic™ carbon FRP type PC26.16 were tested. At the maximum pressure of 250 psig, the maximum hoop strain was 0.2 percent.
‐ In the 12-inch and 6-inch pipes, 2 layers of the PipeMedic™ fiber glass FRP Type PG16.15 were tested. At the pressure of 250 psig, the maximum hoop strains were 0.75 percent and 0.32 percent in the 12-inch and 6-inch pipes, respectively.

An estimate of the applied hoop stress (SH) in the pipes was performed. For the pipe wall thickness t, the hoop stress acting circumferentially on the pipe diameter D due to pressure P is determined by Barlow’s formula:

SH = PD/2t

Table 1 shows the results of the strains and hoop stresses at pressure level of 250 psig in comparison to the ultimate strains and tensile strengths of the composite material.

Table 1 - Hoop stresses and strains of the composite pipe section
Pipe
Diameter
(inch)
PipeMedic™
Composite
No. of
Layers
Hoop
Strain
(%)
Ultimate
Material
Strain (%)
Hoop
Stress
(psi)
Tensile
Strength
(psi)
16
Carbon
3
0.2
0.85
26,641
101,000
12
Glass
2
0.75
1.31
28,846
62,000
6
Glass
2
0.32
1.31
134,423
62,000

The PipeMedic™ carbon FRP in the 16-inch pipe is a high strength material and its hoop stress with 3 layers of the composite) did not exceed 25 percent of its tensile strength at this test pressure.

The PipeMedic™ carbon FRP material was too rigid for use in the smaller diameter pipes and the more flexible PipeMedic fiber glass FRP was used for the smaller 12-inch and 6-inch pipes. The 2-layer laminates of the composite in the 12-inch pipe had a hoop stress of about 45 percent of the material tensile strength. The hoop stress of the composite can be reduced by using more layers of the fiber glass composite to reach a stress level comparable to the rigid carbon fiber.

The PipeMedic™ composite is planned to provide a free-span section across the liquid-separator drip pots in the cast iron gas mains. This process allows for using the CIP liners for the rehabilitation of the pipes without the removal of these in-line fittings. Since the CIP liner system relies on the structural integrity of the host pipe, the PipeMedic section performs similar to the original carrier pipe as per the ASME B31.8 requirements. The testing program evaluated the pressure requirements of the ASME section. Other requirements for the system such as its long-term performance and chemical resistance were not evaluated in this testing program.

Comprehensive Test Report:

To print a copy of the full test report that is available in pdf format, please click here.