Managing Unidirectional Movements (Walk) of HPHT Submarine Flowlines During Startup Heating and Shutdown Cooling IOPF2010-1003• Presenter/Author; Gautam Chaudhury • Company; INTECSEA (Worley Parsons Group) IOPF2010-1003-Chaudhury 1 IOPF 2010 Verification by FEA j .D i magnitude of walk f Derive it d f lk from th thermal gradient h ti l di t heating .Sources responsible for walking and consequences .Overview of Presentation Background of Pipeline Walk .Expansion and contraction of pipelines resting on seabed .Provide procedure for managing walk efficiently Verification and Conclusions .Derive magnitude of walk from unbalanced forces .Examine parameters g p governing p p g pipeline walking g .Major conclusions and use 2 IOPF 2010 .Explain mechanism of walk by ratcheting Determine magnitude of walk and Manage . Expansion and Contraction of Pipeline on Seabed • Pipelines expand and contract due to changes in pressure and temperature subject to resistance from soil • For short pipelines. -The VA location is different during heating and cooling -This results in unidirectional end displacements (Walking) 3 IOPF 2010 . each operation forms a virtual anchor (VA) near or at the middle and the pipe ends move in and out pp • Under symmetric condition net movement is zero • Under asymmetric conditions. (1 − 2. Mathematically the condition is fr < ∆F / L • Where ∆F is defined as the driving force as Where.∆t Fully Constrained Fully Mobilized 4 IOPF 2010 . An apparent fixity p .A.α.Ai. ∆F = (Pi − Pe). Axial displacements occur over the full length.Parameters governing pipeline walking • Virtual Anchor.ν ) + E. pp y point ( p (At proximity to middle) y ) • Full cyclic constraint. No displacement for a portion of length in the middle • Fully mobilized (Short). and th b d l d thermal gradient ( hi h i always present) l di t (which is l t) • Therefore. seabed slope. resistance. soil frictional q y . (High risk) • Loss of SCR tension.Sources responsible for walking and consequences • A unique combination of asymmetric load. for short pipelines there is potential for walking • Magnitude of walk/cycle is small but accumulation may be high • Overstressing of end connectors. and temperature or pressure • Asymmetric load originates from unbalanced end tension. (Low risk) ( ) • Increased load in a lateral buckle (Moderate risk) • Route curve pull out (Moderate risk) 5 IOPF 2010 . 6 IOPF 2010 .Mechanism of walk by ratcheting • • • • Asymmetry from any source shifts virtual anchor off center A t f hift i t l h ff t This is because pipe expansion and contraction is non uniform Unbalanced force is generated between virtual anchors Schematic diagram shows movement of pipe between anchors in the same direction. fr f resistance in strain of the pipeline.A l1 = ( L .(∆ε − ( ) E. fr ) l 2 = ( L . fr − Te ) /( 2 .Sinθ / fr fr = Sw .( fr − Sw.µ 7 IOPF 2010 . Wc Vs [ W = V .Magnitude of walk from unbalanced forces (Assumed Uniform Heating) • S Separation of virtual anchors (VA) produces walk ti f it l h d lk • Magnitude of walk = Driving strain between VA minus total L.A Vs = Te / fr Vs = Sw. fr + Te ) /( 2 .L. fr ) L.Sinθ ) Wc = Vs.[ ∆ ε − ] E. Soil resistance forms VA (not proportional to pipe movement) • Cold VA is always at the middle (Cooling is Symmetric) • Direction of walk is always from hot VA to cold VA 90 80 Tem peratu (Deg C) ure 70 60 50 40 30 20 10 0 0 100 200 300 400 500 600 700 800 900 Element From Hot End 8 IOPF 2010 .Final ∆. This is because .Magnitude of walk from thermal gradient heating Some basic Observations • The heating process is asymmetric (Transient) but end result is as if symmetric (Final hot VA ≈ mid point).t along the pipe length is small . Magnitude of walk from thermal gradient heating Set Up Equation • • • • • Consider the pipeline as several segments of small lengths ‘dl’ Heating occurs from one segment to the next (hot end to cold) At each step VA is at the middle of the respective total length This leads to an equivalent VA at the hot side (walk = > cold) The equation for net magnitude of walk can be expressed as L/2 1 Wc = E.A ∫ 0 L−l [ f θ .l − fr ]. dl 2 Axial Force (KN) F 800 600 400 200 0 -200 -400 -600 -800 800 Node Number 0 100 200 300 400 500 600 700 800 900 9 IOPF 2010 . E. fr dWc ) = (1 − dfr fθ • The derivative of the equation is • Equating this to zero maximum walk is when fr = fθ / 3 q g • ABAQUS analysis with finite mobilization distance fr = 3.Magnitude of walk from thermal gradient heating Solve Equation • Integrating and Using boundary condition Wc=0 when fr=0 L2 fr Wc = ( f θ − 1 . A fθ 3 • Following two conditions were also reported by M. fθ / 8 • Applying ABAQUS based boundary condition 4 L2 fr Wc = ( fθ − fr ) 8. fθ / 8 10 IOPF 2010 . A fθ 3 . Carr et all • For walk to occur fθ > 1.E .5 fr ) 8 . fr • Magnitude of walk is maximum when fr = 3.5. Leads to a situation p g where Fc is highest when walking magnitude is lowest L.L = L.Sw. h i Increase fr to make the pipeline fully constrained Correct Vs by end restraints (Most efficient) active or passive • Thermal gradient case (Active Fc).[∆ε − ] means mitigation force required is small E.L / 2 11 Fc = Vseq.E . A ε avg = α.Qc.A • Th There are t two choices. Vseq = Wc ε avg − fr . fr IOPF 2010 .fr • Fc is independent of magnitude of walk.Managing walk efficiently • The aim is to arrest or reduce walk cost effectively • Past work suggested correction force Fc = µ . fr • Walk Wc=Vs. L 2 . 100KN end tension uniform heating ∆ t = 80 0 C .6 C/Km ( f θ = 1. Sw=1KN/m) .551KN/m) • Mitigation forces were tested by employing end springs and they were found to match well with the predictions 12 IOPF 2010 .1 to 1) Cases examined .01m then kept constant .94e6KN.Seabed slope 1. EA=3.4325 Deg (Eqv to 100KN) ∆ t = 80 0 C .Soil friction linearly mobilized at 0.Verification by FEA (ABAQUS) Pipe/Soil Model .Thermal gradient of 33.Fully mobilized pipe (4Km long.Soil friction coefficient = variable (0. Verification by FEA (ABAQUS) 0.2 0.2 0.12 0.4 0.5 0.4 0.7 0.8 1 Soil Friction Force (KN/m ) Case 3 13 IOPF 2010 .8 1 Soil Friction Force (KN/m) Prediction Eqn=10 ABAQUS FEA Case 1 Walk (m/Cycle) 0.14 0.08 ABAQUS FEA 0.9 0.4 04 0.6 0.8 0.8 0.4 04 0.04 0.2 0.02 0 0 0.5 0.16 0.9 0.1 0 0 0.2 0.6 0.6 0.8 1 Soil Friction Force (KN/m) Prediction Eqn=9 ABAQUS FEA Walk (m/Cycle) ( 0.2 0.4 0.6 0.3 0.6 0.3 0.7 Walk (m/Cycle) ( 0.1 Case 2 Prediction Eqn=17 0.06 0.1 0 0 0. Major conclusions and use • Short HPHT pipelines have high potential for walk • Accumulation of walk over the field life may pose risk • Proposed tools provide accurate walk and mitigation forces • Managing walk by end restraint method is most cost effective • True physical model is more complex and case dependent p y p p • Primary uncertainties are friction coefficients. and gradient heating. and planning for final g FEA design check. understanding the parametric influences. 14 IOPF 2010 . mob-distance. specially for theoretical predictions • Analytical tools are given for preliminary screening. [email protected] You for Your Attention • Future Contact: • Gautam Chaudhury • T l 281 925 2443 Tel.com • INTECSEA/Worley Parsons Group 15 IOPF 2010 . gautam.