Can a Design Engineer Rely on D/t Ratio as a Rational Indicator to Manage Stresses and Strains in Welded Steel Pipe During Handling?

Abstract

The choice of initial wall thickness in welded steel pipe design is accomplished by following an empirical formula with the objective of managing stresses and strains in the pipe wall during handling. Stresses and strains during handling are due to a number of factors, including lifting with slings, placement on supports, and shipping to name a few. Although the avoidance of cement mortar lining (CML) cracking before or during stull installation is of primary interest in this paper, the need to manage the strain level in steel to prevent having an adverse impact on the integrity of CML is also discussed. With a flexible lining, the design engineer has more latitude. To avoid excessive stresses and strains, for decades, design standards and manuals have provided empirical formulae as a diameter to thickness (D/t) ratio criterion. Given that water pipes carry relatively low internal pressures in many projects, the choice of initial wall thickness often ends up as the final thickness of the steel pipe. The question that has not been asked by engineers for over eight decades is Can a Design Engineer Rely on D/t Ratio as a Rational Indicator to Manage Stresses and Strains in Welded Steel Pipe during Handling? The authors of this paper embarked on an investigation to answer this very question. The authors share their methodology, results, findings and suggestions for improvement in current practice.