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FIGURE 4. Example of the tensile response       like PolyUMod® library from              Ernest Lever, R&D director (left) and Oren Lever,
of PE and the model t made by Veryst            Veryst Engineering.                      principal engineer (right) at GTI.
Engineering (bottom) and accelerated lifetime
tests for the PE pipe squeeze-off performed by     With simulation, GTI was able to      GTI is helping set new guidelines that
Gas Technology Institute (top).                 determine that in the case of small-     will make the current gas pipeline
                                                diameter pipes (smaller than 3.5”) the   maintenance process less expensive,
optimization tool they developed to             closer squeeze-off distance of three     more ef cient, and less invasive.
vary parameters until a very good t             pipe diameters did not cause strains
of experimental data is discovered. To          over current industry-accepted              Regarding plans for further research,
implement and verify the calibrated             strain limits.                           Lever says their team plans to expand
material law in COMSOL Multiphysics,                                                     the constitutive model to include
Veryst relied on the software's                    They used additional accelerated      temperature and creep in order to
                                                lifetime testing (shown in Figure 4) to  describe relaxation effects more
  exibility by adding a system of ODEs          validate these results. Squeeze-off was  accurately. The goal is to be able to
representing additional states used to          tested at two and four inches from the   perform damage propagation and
describe the custom constitutive model.         fused coupling at temperatures high      failure analysis to predict the behavior
                                                enough to accelerate the creep rate in   of the pipe for different load scenarios,
   Another option, useful in those              the polyethylene when compared to        such as the installation of
cases where a material model cannot             normal operation. Through this extra     reinforcement clamps.
be described by equations, would                testing, the team at GTI discovered
have been to use the External Material          that the pipes would have an 80-year        GTI will also look into making
feature to access functions written in          lifetime when operating at an average    their ndings available to engineers
FORTRAN or C code and compile them              temperature of 20ºC. This agrees with    not necessarily versed in numerical
into a shared library. In that case, the        the standard industry lifetime of 80     simulation. As COMSOL users they have
external material can be de ned by              years for MDPE gas pipelines.            access to the Application Builder, a tool
the stress-strain relation, simply return                                                that allows simulation specialists such
an inelastic strain contribution to the         ð EFFICIENCY IS KEY FOR                  as Lever to wrap a COMSOL model in
material model in use, or link directly to      FUTURE PLANS AT GTI                      a custom user-friendly interface. This
a commercial external material library                                                   means that engineers on the eld and
                                                From their simulation work, GTI found    maintenance staff involved don’t have
                                                that the squeeze-off location on small   to second-guess their choices, especially
                                                diameter pipes can be closer to the      in unusual operating scenarios.
                                                                                         Meanwhile, simulation specialists save
                                                  tting than the current minimum         time and can focus on a new project.
                                                distance allowed under the ASTM          For now, GTI continues to devote their
                                                standard. This con rms that the          research and development efforts to
                                                current twelve-inch minimum distance
                                                requirement can be reevaluated           natural gas and energy innovations. v
                                                for smaller pipe diameters, which
                                                are the most commonly used sizes
                                                for residential and commercial gas
                                                applications. Thanks to their research,

20 COMSOL NEWS 2016                                                                      PolyUMod is a registered trademark of Veryst Engineering, LLC.
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