Mechanical Characteristics of a Large Diameter Expansion Joint Element, “Snake Pipe”

Abstract

Expansion joints are important elements to absorb thermal expansion or long-term deformation of piping in heat transfer, gas or liquid transportation systems. In most cases, expansion joints have been prepared by using bellows, fabricated from stainless steel of thickness 1mm to 2mm. This solution is easy for metal forming in fabrication, but has a big difficulty to apply in under ground piping system. Main problem is the electrolytic corrosion due to the difference in ionization potential of materials between the bellows and main line pipes, which are usually made of carbon steels or low-alloy steels. Local corrosion troubles have often appeared by the effect of under-ground stray currents in long term service.
In order to overcome these problems, an expansion joint element was developed by bulge forming of pipes of the same steel as the main line pipes. This element was named as “snake pipe”, and have been extensively used in various application. For the purpose to provide design informations, a series of tests were conducted to examine the mechanical performance of the “snake pipe” specimens.
The present paper reports on the results of three basic loading tests; (1) axial loading, (2) internal pressure, and (3) bending, together with the examination of the precision of geometry and of the change in mechanical properties of materials during the forming process. The stress distribution obtained by strain gauge measurement were compared with an energy-approach solutions by Palmer under axial loading. The mechanical behaviors of “snake pipe” specimen were characterized by using a simple compliance model and compared with those of the reference straight pipe for the convenience to apply to the expansion joint design.