Theoretical formulas were developed which provide a means of computing the stresses in and near a tapered transition joint when the shell is subjected to internal pressure. The theoretical equations for stresses are compared with test results in which stresses were measured at and near tapered transition joints by means of electrical-resistance strain gages. Theory and test results are in adequate agreement. Since the resulting theoretical equations are quite complex, graphs of precalculated factors are shown to enable rapid calculation of the significant stress in any tapered transition joint in the dimensional range of wall-thickness ratios from one to two; and with transition tapers from an abrupt transition to a very small slope. The theory and graphs cover joints in which (a) the transition taper is both inside and outside of the shell to produce a geometrically balanced construction; (b) taper on the inside of the shell only; (c) taper on the outside of the shell only.
A procedure for predicting the increase in fatigue load carrying capacity due to presetting helical springs is developed, based on the actual stress-strain curve of a material. Reasonable correlation with experimental results is obtained. For the cyclic load conditions and the material chosen, an increase in load carrying capacity of 21 per cent was observed. It is expected that an increase of approximately 40 per cent could be realized with slight modification of fabrication techniques.
The report covers the information gained through discussions with pipe manufacturers, previous field failure investigations, and other reports and information made available. Good insight into the important factors that affect the possibility of fatigue damage during shipment was gained. Knowledge now available, although not complete, is sufficient to provide some guidelines to minimize transit damage and thus, we are recommending that a supplement to the AAR rules for loading pipe be prepared.
This report is the third in a series of reports dealing with the behavior of corroded line pipe. In this phase the data from the first two phases and the results of other studies of defects are reanalyzed for the purpose of optimizing the predictive capability. In addition, this report includes guidelines to suggest how one might go about setting criteria to accept or reject pipe for gas service on the basis of the predicted remaining strength.
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