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• <br />In the early 1960's work was undertaken by the American Gas <br />Association Pipeline Research Committee to establish limits for <br />charge size (pounds per delay) and distance from a blast to high- <br />pressure gas transmission lines. The primary research found that <br />there had been no reported case of pipeline failure due to normal <br />blasting activities. Only when explosives were detonated directly <br />adjacent to a pipeline were failures recorded. <br />To be able to predict if the stress produced in a pipeline by <br />nearby blasting activities is enough to cause failure one must <br />assume: <br />1. Soil displacements can be adequately predicated by scale <br />distance formulas. <br />2. The pipeline movements are equal to those of <br />the surrounding soil. <br />• <br /> <br />These assumptions result in a very conservative predicted free <br />field soil stress. <br />Two types of pipe stress are considered: axial stress, and <br />circumferential stress. The allowable pipe stress is determined by <br />American Petroleum Institute guidelines. Pipe diameter, pipe wall <br />thickness, specified minimum yield strength, maximum operating <br />pressure, pipe modulus, and the design factor must be known to <br />calculate this. Other factors that should be considered include: <br />thrust blocks, thermal movements, residual stresses, overburden <br />thickness, and pipeline condition. Unfortunately, it is hard to <br />obtain this information for most older pipelines and many new <br />pipelines. <br />In one. example, a pipeline company requested that the maximum <br />allowable pipe stress be held to 2,500 PSI. The pipeline was <br />measured with strain gauges and seismic particle velocity <br />recorders. The 2,500 PSI allowable pipe stress was never reached <br />but the closest blast was five feet away from the 22" diameter pipe <br />and did have a measured particle velocity of 9.85 inches per <br />second. ' <br />For the best protection, pipe condition, pipe attributes and design <br />factor should be known, and both strain gauge and particle velocity <br />measurements should be taken. <br />Sincerely, <br />C--c~'V <br />Colin M. Matheson <br />Area Manager <br />Vibra-Tech Engineers, Inc. <br />9 <br />