Offshore industry is now pushing into the deepwater and starting to face the much higher energy reservoir with high pressure and high temperature. Besides the significant impacts on the material, strength, and reliability of the wellhead, tree, and manifold valve; high Pressure (HP) also leads to thicker pipe wall that increases manufacturing and installation cost. High Temperature (HT) can have much wider impact on operation since the whole subsea system has to be operated over a greater temperature range between the non-producing situations such as installation, and long term shut down, and the maximum production flow. It is more concerned for fact that thicker wall pipe results in much greater thermal load so to make the pipeline strength and tie-in designs more challenging. Burying sections of a HPHT pipeline can provide the advantages of thermal insulation by using the soil cover to retain the cool-down time. Burial can also help to achieve high confidence anchoring and additional resistance to the pipeline axial expansion and walking. Upheaval buckling is a major concern for the buried pipelines because it can generate a high level of strain when happens. Excessive yielding can cause the pipeline to fail prematurely. Partial burial can have less concern although it may complicate the pipeline global buckling behavior and impose challenges on the design and analysis. This paper presents the studies on the upheaval buckling of partially buried pipelines, typical example of an annulus flooded pipe-in-pipe (PIP) configuration. The full-scale FE models were created to simulate the pipeline thermal expansion / upheaval / lateral buckling responses. The pipe-soil interaction (PSI) elements were utilized to model the relationship between the soil resistance (force) and the pipe displacement for the buried sections. The effects of soil cover height, vertical prop size, and soil resistance on the upheaval and lateral buckling response of a partially buried pipeline were investigated. This paper presents the latest techniques, allows an understanding in the global buckling, upheaval or lateral, of partially buried pipeline under the HPHT, and assists the industry to pursue safer but cost effective design.
Uplift soil resistance to a shallowly-buried pipeline in the sandy seabed under waves: Poro-elastoplastic modeling
