Straight Talk About Riser Tension and More

One of most confusing issues in riser engineering is the riser tension. The infamous effective tension equation relates it to the so-called material tension with external and internal pressures. Controversy remains after numerous papers published trying to clarify the subject, because different interpretations were presented by different authors. Instead of explaining this ‘abstract’ equation mathematically using the free body diagram and differential equation as done in the literatures, this paper presents a down-to-earth interpretation that follows the riser loading history which starts with the Effective Weight to re-derive the same equation. Four keys to solve the riser tension mystery are identified; they are the hydrostatic head pressure vs. applied pressure, pressure generates the pressure end cap load vs. none generated, the vertical (top-tensioned) riser vs. bent (catenary) riser, and the single string riser vs. multiple strings riser. Based on these four keys, this paper will address the difference between the effective tension and material tension and identify which tension is to be used in the stress calculation. Also presented in the paper is the driver-reactor theory developed to explain the tension load distribution among riser strings due to Poisson’s effect with the applied pressure.