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Title: Research On Stresses In Burned Gas Pipelines Subject To Combined Loadings
Author: J. m. Arnold, H. A. Todres, N. C. Saha, m. Mcclinton
Source: American Gas Association 1985
Year Published: 1985
Abstract: As part of the Distribution Research Center Task project conducted by the Institute of Gas Technology under sponsorship by the Gas Research Institute, a series of field and laboratory tests was performed to determine the influence of combined loads on pipe structural (stress/ strain) behavior. Three field test sites were constructed near Racine, Wisconsin, along a 30- year-old operating pipeline. Both the pipeline (a 16-inch, 0.25-inch wall thickness, 300-psig maximum allowable operating pressure steel gas main) and the surrounding backfill were extensively instrumented with strain, pressure, temperature, and moisture sensors and with accelerometers. Subsequently, a state highway was built over the instrumented sections such that three depths of cover (top-of-pavement to top-of-pipe distance) resulted: 1 A, 3, and 6 feet. Data were acquired over a 2-year period and analyzed. In one phase of the analysis, the acquired data were compared with results obtained from several models. The models ranged in complexity from simple closed-form solutions based on the well-known Barlow equation for stresses induced by internal pressure to a finite element method, CANDE, recently developed as an aid to Culvert ANalysis and DEsign. The models evaluated were found to be conservative in their predictions of hoop stress, but they were not able to pinpoint where on the pipes circumference the highest stresses were occurring. In another phase of the analysis, the acquired data were compared systematically in computerized bivariate/multivariate analyses from which empirical equations were obtained that expressed pipe stress in terms of several measured variables. Closed-form solutions then were matched to the empirical equations to obtain formulas for uniform hoop (circumferential) stress and uniform axial (longitudinal) stress. The results of both phases then were combined in a model, EMPP, that more comprehensively predicts the hoop stress in an EMbedded Pressurized Pipe under combined loads other than vehicular loads. The EMPP model achieved a very high correlation (r 0.99) with the acquired data, indicative of its potential to describe accurately the state of hoop stress in a gas pipeline buried in close proximity to the ground surface in the absence of vehicular loads. To evaluate the effects of vehicular loads, comparisons were made between field measurements and predictions of several models. Two models developed by use of an elastic-layer theory predicted soil stresses and strains that closely agreed with measurements obtained during traffic tests, and a simple hydrostatic model provided pipe stress predictions within 50 psi of the actual measurements.

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