Session: 04-04-04 Lateral Buckling and Reeling

Paper Number: 123740

123740 - Pipeline Lateral Buckling Mitigation With Combined Sleepers and Mattresses 

Under thermal compressive forces due to operating temperature and pressure, pipelines may buckle laterally if the axial force is higher than the buckle initiation load (or critical buckling load). If uncontrolled, global buckles may result in pipeline over stressing or high thermal fatigue damage. 

Buckle-initiation devices, such as sleepers and distributed buoyancy modules, are usually adopted to initiate lateral buckles at pre-determined locations to release the thermal expansion in a controlled manner and ensure pipeline integrity. For pipelines installed by S-lay, sleepers are desired as it is difficult for buoyancy modules to pass over the stinger rollers. If the thermal cyclic fatigue is critical in the pipeline design due to high operating temperature and pressure, high soil uncertainties, a large number of operating cycles, and degradation of fatigue performance due to service conditions, pipeline lateral buckling designs may result in small sleeper spacing. As such, buckle reliability (i.e., the pipeline will buckle at all planned locations independently) of conventional sleepers may be inadequate in some cases. 

Water injection pipelines are utilized to examine lateral buckling mitigation with sleepers. These pipelines are on very soft clay and will be installed with a S-lay vessel. The operating temperature is relatively high and thus lateral buckling mitigation is required. 

In this paper, lateral buckling mitigation with sleepers is investigated using finite element (FE) models. Sensitivity analyses are performed on key input parameters. Discussions are made for parameters including single and dual sleepers, lower bound and upper bound friction factors between sleeper and pipeline, berm (at the sleeper span touch down areas) effects on soil lateral resistances, and sleeper heights. The pipeline strength and fatigue are assessed with API RP 1111 and DNV-ST-F101.

Based on the sensitivity study results, a mitigation solution combining sleepers and mattresses under the pipeline touch down points is further evaluated. It is found that sleepers combined with reduced touch down point lateral friction can reduce the maximum longitudinal strain and thermal fatigue damage by more than 50% as compared to using sleepers alone as mitigation. Therefore, this design adds a new option to allow increases in the sleeper spacing and improved reliability of buckle initiation. Parametric studies are performed for this mitigation design, which also demonstrate that the lateral buckling results are not sensitive to the mattress location, friction between the mattress and pipeline, mattress width, and mattress height or penetration into the soft clay. 

In all, this paper provides a new option of lateral buckling mitigation for improved reliability of S-lay pipelines.

Presenting Author: Kevin Hayes Genesis

Presenting Author Biography: Kevin Hayes is a Subsea Delivery Manager for the Houston office of Genesis, a business unit of Technip Energies. He has worked for 22 years in the energy industry in Houston, Texas and 27 years in total focusing on the use of finite element analysis to solve a wide range of industry problems. He received his Bachelor of Science degree in Mechanical Engineering from Rose-Hulman Institute of Technology and his Master of Science degree in Bioengineering from Clemson University. Kevin’s work over the past ten years has been in the area of subsea pipelines and subsea department management. This work has included subsea project management and in-place pipeline analysis with a particular focus on global buckling, walking, and pipeline responses to in-situ loading.

Kevin is also a Senior Technology Expert in Mechanical Finite Element Analysis in the Technip Energies Expertise Program.

Authors:

Kevin Hayes Genesis
Xinhai Qi Genesis
Gang Duan Golden Shield Technology
Lan Ren Golden Shield Technology
Joe Jin ExxonMobil
Akhilesh Sharma ExxonMobil