J-Lay Pipeline Welding
Authors: Laing B.S. , Hoyt D.S. 
Published: October 2008

Development of deep water oil and gas reserves require pipeline installation using J-Lay methods, limiting the number of working stations to 1 with the pipe axis vertical. This program researched the welding technology for J-Lay pipeline welding. It was found, with minor modifications, the narrow gap welding technology used for conventional offshore construction could be used effectively for J-Lay pipeline welding. Welding procedures were developed, mechanical properties tested and a simulated field trial performed successfully.

INTRODUCTION

Conventional offshore pipeline installation is done with the pipe axis in the horizontal position (5G) on the "lay barge". The lay barge typically have a series of tensioners to hold the pipe into an "S bend. This technology is not suitable for "deep" water. The maximum effective depth for S-Lay is dependent on the pipe diameter and lay vessel characteristics. For pipelines in water depths beyond S-Lay capabilities, the J-Lay technique must be used.

The J-lay technique places the pipe axis in the vertical position (2G) on the lay barge with a continuous radius to the sea bottom. Generally, this technique reduces the tension required and makes it possible for much smaller vessels to perform the pipelay operation. The major limitation of the J-Lay technique is the number of working stations. A conventional lay barge will have 5 to 10 working stations. The work of welding, inspection, repair, and field coating is divided over these stations to maximize production. In the case of J-Lay construction all these functions must be performed in one station making the cycle time of adding one pipe length much longer than on a conventional barge.

This group sponsored program was organized to research the application of high productivity, narrow gap, welding technology normally used for conventional pipeline welding for 2G pipeline construction. The sponsors of the program were:AMOCO Corporation BP ExplorationChevron Corporation Conoco, Inc.Exxon Production Research Kawasaki Steel Corp.Shell DevelopmentSumitomo Metal America, Inc.The program was carried out in 8 separate phases. They were:Phase 1- Equipment ModificationPhase II - Process EvaluationPhase Ill - Joint Design EvaluationPhase IV - Welding Position EvaluationPhase V - Welding Consumable EvaluationPhase VI - Pinal Procedure EvaluationPhase Vll - Cooling rate MeasurementPhase Vlll - Mechanical Property Testing

MATERIALS

The pipes used in this investigation were:24-inch-diameter, O.810-inch-wall, double-submerged-arc welded (DSAW), API 5LX-60 grade, and16-inch-diameter, 0.740-inch-wall, seamless, API 5LX-60 grade. The 24-inch-diameter pipe was controlled-rolled, accelerated-cooled (TMCP). The 16-inch- diameter pipe was quenched-and-tempered. The chemical compositions of these pipes are shown in Table 1.

Both metal-core and solid filler wires were evaluated during Part II, Process Evaluation. The metal-core electrode was 0.035-inch-diameter, Alloy Rods, Coreweld 70 of the AWS E 70 T-1 classification. Solid wires of 0.035,0.040 and 0.045-inch-diameter of the four alloy groups, C-Mn, C-Mn-Ni, C-Mn-Ti, and C-Mn-Ti-B were used.

The chemical composition of these solid, filler wires is shown in Table 2.