CNST-2-2: Guidelines for the Determination of Pipeline Lowering-in Stresses and Mitigative Strategies for Construction
The Design Materials & Construction (DMC) Technical Committee’s focus for the past quarter has been on completing the updates of the research plans for the seven DMC Emphasis Areas leading to the development of research ideas for the coming annual funding cycle. These areas cover the spectrum of DMC responsibility including: Assessment & Repair, Design, Construction, Materials, Fracture, Geohazard Management and Welding.
Several DMC projects achieved significant milestones in the past year, delivering products that could be used by operators, now. These were presented to the membership at the annual Research Exchange that was completed in February.
By the end of the first quarter of this year over 80% of the projects funded for 2016 had been awarded. Project Teams have approved proposals for two of the remaining three projects with the other one being finalized now in response to guidance from that Project Team.
Efficiency in design and construction remain high priorities. The following ongoing project achieved a major milestone by the February Research Exchange by providing operators and constructors an important new capability.
CNST-2-2 Guidelines for the Determination of Pipeline Lowering-in Stresses and Mitigative Strategies for Construction. During construction of a cross-country pipeline, bending stresses are produced when the pipeline is lifted and lowered into the ditch. It is critical to limit stresses that occur during lifting and lowering-in so that damage to the pipeline is avoided. There is little in the way of formal guidance in current codes and standards for controlling stresses during lifting and lowering-in activities. At present, two dimensional analysis and methodologies are generally employed to assure that the lifting and lowering-in stresses are maintained within allowable limits. The approach generally used has been to conduct a static analysis on level ground with the pipe shape as defined by an S-curve with all side booms equally spaced, taking up their portion of the load. There has been a very limited amount of three dimensional analyses conducted to simulate the actual pipe lowering operations with varying terrain and distances between side booms. Also, while individual operators have internal guidelines, there is not a comprehensive industry guidance document for this phase of construction that can be used by both owners and contractors. This project is intended to satisfy that requirement.
The project has recently delivered a basic product that provides this capability for three specific pipe diameters and for reasonably level terrain. Work continues to include the following enhancements: extend the streamlined analysis capability to all pipe diameters, cover depths, and side boom spacings within given ranges; extend the applicable pipe diameter range; and develop a standard application tool suitable for both operators and contractors that includes correction factors that can be used for construction in hilly terrain. This next generation product will be an easy-to-use application tool that will enable the ready selection of operational parameters to assure stress levels during the lifting and lowering-in processes under a wide range of conditions. Pipeline owners and contractors will benefit by having access to construction best practices, the use of which will result in the desired integrity of completed pipeline systems. This PRCI project has been a jointly supported initiative including IPLOCA and the INGAA Foundation. (CNST-2-2)