|Abstract or Summary
- Polyethylene has been used extensively for natural gas transport since
the mid-1970's. The pipeline system is sound and well-functioning, but there
are some aspects of the system that could be improved. One of these is the
repair method of leaking pipes. Presently if a natural gas pipe begins to leak,
the damaged pipe is completely excavated. The pipeline around the
damaged area is clamped to seal the pipe and stop the gas flow. The bad
piece of pipe is cut out, and a new piece is welded in place. Often, with the
passage of time, these welds leak. This is not dangerous but it is costly.
The current research focuses on the viability of using a polyethylene
patch and a commercial adhesive to seal a leak in the natural gas pipeline.
The patch would be applied to the pipe through a keyhole excavation (18"
diameter) with a tool designed and manufactured by Timberline Tool. This
tool offers an advantage because repairmen will be able to operate the tool
from the ground level through a single keyhole excavation, and possibly
without stopping the gas flow in the pipe depending on the leak size.
Four commercial, acrylic-based, structural adhesives were analyzed for
bonding the patch to the natural gas pipe. Three of the adhesives are
manufactured by 3M Worldwide, DP-8005, DP-8010, and DP-8OIONS. The
fourth is manufactured by Henkel Loctite, Loctite 3030. The cure kinetics of
the adhesives were studied with differential scanning calorimetry (DSC)
experiments. The material and mechanical properties of three types of
polyethylene substrates (HDPE, pipe MDPE, and pressed MDPE) were
studied with tensile testing, contact angle analysis, DSC experiments, atomic
force microscopy, and scanning electron microscopy.
Previous research of determined the bonded patch must be able to
withstand up to 500 psi of shear force with an internal pipe pressure of 100
psi (normal pressure in the pipeline is 65 psi). Overlap shear tests were
used to analyze the shear strength of the bond between each adhesive and
the different polyethylene substrates. The shear tests were used to
determine the optimal cure conditions of the adhesives.
One adhesive, DP-8010 from 3M, was proven to be appropriate for
bonding a polyethylene natural gas pipe. When this adhesive is cured under
optimal conditions, and the surface of the polyethylene substrate is prepared
properly, consistent shear strengths between 800 and 1400 psi can be