Development of Welding Procedure Specification for Girth Welds in Coiled Tubing

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAs oil and gas well servicing operations involve increasingly larger coiled tubing (CT) sizes, the ability for extending their useful or working life becomes of increasingly greater economic importance. Not only do larger tubing sizes exhibit inherently lower fatigue lives, but also their replacement cost is considerably greater. Efforts are underway elsewhere for developing CT repair strategies for recovering some of the CT fatigue life that has been reduced due to dents and other damage or degradation of the tubing. Such local repair methods, however, have both material and practical limitations. The capability to remove finite section(s) of tubing that has been damaged or expended a greater percentage of its working life, would be of significant benefit rather than force the retirement of the complete tubing string. Removing sections of excessive ovality and subsequent replacement with new sections without discarding the complete tubing or the ability to extend the CT string length, are further examples of the benefits of performing reliable on-site girth-welded connection(s) in coiled tubing. This paper describes the weld procedure specification (WPS) under development at BJ Services. The procedure utilizes an orbital tungsten inert gas (TIG) welding process equipped with a full-function "Magnatech D-Head". The welding sequence consists of a fine stringer bead technique for maximum grain refinement and a strategic control of heat input, preheat and interpass temperature control. Mechanized systems for tubing ovality removal, reaming of internal ERW seam weld flash and girth-weld edge preparation, are utilized to their fullest extent to maximize repeatability of the weldment integrity and minimize reliance on welder skill and quality of workmanship. Preliminary test results obtained indicate that the low-cycle plastic fatigue life of these mechanized girth welds can be increased by at least 100% compared with what is generally attainable from manual TIG girth welds in coiled tubing.

High-Cycle, Low-Cycle, Extremely Low-Cycle Fatigue and Monotonic Fracture Behaviors of Low-Carbon Steel and Its Welded Joint

“…The weld metal showed coarse granular bainite with the average grain size of 33.8 µm in diameter (Figure 3c), but the structure was finer than that produced by gas tungsten arc welding process, because plasma arc welding process provides focused heat transfer that results in a lower heat input leading to improved penetration in the smaller heat-affected zone [32]. Previous studies observed fatigue fractures at the softened HAZ [5,6]; however, the inferior coarse WJ microstructures with low hardness produced using a welding consumable with low strength or a process with high heat input can cause fatigue fracture [3,4].…”

“…For practical application, steel parts are usually joined by welding, which can introduce residual stresses and heterogeneous microstructures [1,2] that can result in locally inferior mechanical properties compared to the base material. For example, the fatigue life of welds is shorter than that of the base material due to welding defects [3,4] or heat-affected zone (HAZ) softening [5,6], where fatigue fracture occurs in these regions. Low-carbon steels are readily joined with several common fusion welding processes such as plasma arc welding (PAW) and gas tungsten arc welding (GTAW), but some studies [7][8][9] reported that friction stir welding process as an solid state welding showed superior fatigue strength due to the synergetic effect of microstructure, superior tensile properties and favorable residual stress, which inhibit the growth of cracks compared to other joints.…”

Welding Thermo Cycle and HAZ Softening of CT80 Butt Weld Joint

“…butt welding of plate, tube forming welding and butt welding of coiled tubing on site. For CT80 tubing, the strength is high and the wall thickness is thin, the steel is made through TMCP process, and the crystal granular of steel is fine, gas tungsten arc welding (GTAW) welding method is generally used [3,4,5,6]. The working condition of coiled tubing is special, high strength and high plasticity is also demanded for the welded joint.…”

Mössbauer characterization of joints of steel pieces in transient liquid phase bonding experiences

“…It is well known that the present welding method has severe limitations in field application. Also there is a correlation between the quality and repeatability of the welds and the skill of the welding operator [2].…”