Shoulder Yielding Detection During Pipe Make Up
Authors: Ruehmann Rainer , Ruark Graham 
Published: May 2011

During makeup, shoulder connections can become deformed by over-torque or contamination in the thread compound. The result is a reduction of the inner diameter of the connection at the shoulder and potential leaking during service. A yielded connection must be rejected, broken out, and the pin and box diameters and threads inspected for deformation or damage (VAM book, December 2010) [1]. In most cases, the tubular(s) must be removed from the string and replaced.

If over-torque is the root cause for yielding, it is normally easily detected by indication of final torque (dump torque) being greater than the set point value on the torque-turn graph. Currently, yielded connections are detected by the operator visually inspecting the torque-turns graph; a subjective process dependent on the operator's knowledge and experience.

A new software process detects yielding in a connection during makeup by evaluating the change in gradient in the delta turns range (between shoulder contact and final torque) of the makeup graph. The gradient value initially increases to a value that should remain relatively constant until final torque is achieved. A decrease in the gradient during the delta turns range of the makeup is a potential sign of yielding.

This paper discusses a mathematical approach for analyzing a makeup in real time and detecting possible yielding based on analysis of the torque-turns gradient in the delta range of the makeup graph.

Introduction

Well integrity depends on proper tubular makeup. Tubular connection manufacturers provide running procedures that detail the cleaning, inspection, and makeup parameters for their connections; typically torque-turn monitoring is used to verify that connections are properly madeup. [1] The incident that triggered the development described in this paper occurred in the Gulf of Mexico in early 2010. A tubing string of 5 ½ inch, 26 ppf, 25Cr VAM Top was run in the hole in a routine completion. An attempt to set a plug in the lower most landing nipple revealed a significant restriction in the ID (inner diameter) of the tubing string well above the target setting depth. A gauge ring run determined that the nominal tubing ID of 4.548 was reduced to less than 4.375.

Yielding of a connection resulting in a reduction of the ID is usually caused by over-torque of the connection during makeup. In the cited case, extensive investigation determined that the torque measurement systems were properly calibrated and no mechanical conditions appeared to prevent the power tong from applying the correct torque. Examination of the torque-turn makeup plots for the string showed a number of connections that indicated slight yielding of the torque shoulder. The amount of yielding visible on the torque-turn plots, however, did not indicate the actual yielding that occurred in the connections. A subsequent Root Cause Analysis (RCA) showed that the yielded connections were caused by water contamination of the thread compound. This contamination significantly reduced the friction factor and effectively caused excessive delta turns during makeup even although the correct torque was applied [2].