HotPipe JIP: Design Guidelines for HP/HT Pipelines

Abstract

Recent development plans envisage the transport of hydrocarbons at temperature and pressure conditions far more severe than in past projects. Technical feasibility of certain inter field lines was put in doubt as a consequence of application of design guidelines currently in force. This fact gave rise to a critical review of design criteria. The HotPipe Project is a Joint Industry Research and Development Project, whose overall objective is to prepare a DNV Recommended Practice to be used in structural design of high temperature/high pressure pipelines. The DNV-RP will cover most practical cases where pipelines are subjected to high internal pressure and high temperature (HP/HT). The design criteria are based on the application of reliability methods to calibrate the partial safety factors in compliance with the safety philosophy established by DNV OS F101. The overall objective was pursued by performing the following subprojects: • Pipe Capacity: Experimental tests were carried out and FE models were developed aiming at establishing the failure mechanisms of thick pipes subjected to internal pressure, bending moment and axial compression under monotonic and cyclic loading conditions. • Pipe Response: Analytical tools and FE models were developed for studying the localization of buckling pattern for the envisaged pipeline scenarios i.e. pipelines laid on even sea bed, pipelines laid on uneven seabed and buried pipelines. • Mitigation Measures. Study of relevant mitigation measures and associated criteria for preventing/reducing/controlling additional pipeline bending. • Design Guideline. Preparation of the design guideline. The Joint Industry Project Hotpipe did recently finish the work and issued an internal confidential project guideline. This is in the process of being converted into a public DNV Recommended Practice, ref. DNV-RP-F110, which will be published later this year. It provides procedures and criteria to fulfill this functional requirement, to ensure the integrity of the pipeline in the post buckling condition. This paper will describe the procedures and criteria in the project guideline. It is expected to be identical in the coming RP issued for industry hearing. This paper describes the main structure and the covered design scenarios of the DNV-RP, particularly: • Pipelines exposed on even seabed, where thermal expansion may be accommodated by lateral snaking; • Pipelines on uneven seabed corresponding to even seabed; and • Pipelines on bottom of trenches/covered by natural or artificial backfill.

Parametric solution of lateral buckling of submarine pipelines

“…Buckling analysis of pipelines has created considerable interest in the past due to the complexities involved in the analysis. JIP projects [11][12] have provided a general overview of buckling phenomena and solutions derived from classical theory. However, the separate effects of soilpipeline interaction, pipe material and geometry on the buckling initiation load were not properly identified and discussed.…”

“…The axial pipe-soil stiffness is given as [17] 𝑘𝑘 𝑥𝑥 = 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝜃𝜃 𝐷𝐷 (11) where kx is the axial soil stiffness, m is the constant of shear modulus (G = mz, z is the depth below the pipe), and θD is the embedment angle of the pipe as discussed in the previous paper. The axial elastic stiffness, kx span a range of 0.04 to > 200 kN/m 2 was considered here.…”

“…Joint industry projects (JIPs) such as the previous HOTPIPE and subsequent SAFEBUCK projects developed guidelines addressing the buckling phenomena related to HT/HP pipelines [11][12]. In these projects the buckling of subsea pipelines subjected to internal pressure and temperature changes was investigated.…”