a pipeliner's perspective on longwall mining -...
TRANSCRIPT
IntroductionIntroduction• There are over 300,000 miles of gas
transmission and 175,000 miles of liquid transmission pipelines in the United States– Historically, many of these pipelines run from the
Gulf Coast to the NortheastA significant number of these pipelines run– A significant number of these pipelines run through the eastern coalfields with their associated longwall mining
– Interstate pipelines are regulated by the DOT
What Could Possibly Happen?What Could Possibly Happen?
OverviewOverview
• KAI approach for mitigating the effects ofKAI approach for mitigating the effects of longwall mining on high-pressure pipelines:pipelines:– Perform an integrity analysis of pipeline
Perform a longitudinal stress analysis to– Perform a longitudinal stress analysis to determine the existing stress on pipeline
– Estimate stress from subsidence– Estimate stress from subsidence – Develop a formal mitigation plan
Integrity AnalysisIntegrity Analysis
• This is the Single Most Important StepThis is the Single Most Important Step• A Pipeline is Not Just A Pipeline
Th i– They vary in age:• Nearly 15,000 miles were built before 1940• 185 000 miles were built between 1940 and 1970• 185,000 miles were built between 1940 and 1970
– Pipe fabrication and construction practices have seen considerable change over thishave seen considerable change over this period
Something You Don’t See Anymore-Wrinkle Bends
Integrity Analysis-Why do It?g y y y• Subsidence increases the longitudinal
t th i listress on the pipeline– This stress increase can result in the failure of
d f t th t ld t b f ddefects that would not be of concern under normal operating conditionsE l– Examples
• Circumferential corrosion and stress corrosion cracking (SCC)
• Pre API 1104 girth welds• Coating can be damaged
Integrity Analysis ProcessIntegrity Analysis Process
• IncludesIncludes– A review of the history of the pipeline,
Review of in line inspection reports (if– Review of in-line inspection reports (if available), and
– Review of girth weld inspection reports (if– Review of girth weld inspection reports (if available)
• A girth weld is the weld used to join individual g e d s e e d used o jo d dualengths (aka joints) of pipe.
Existing StressExisting Stress
• Hoop stress due to pressureHoop stress due to pressure
L it di l t d t• Longitudinal stress due to pressure
• Longitudinal stress due to temperature
Additional Existing StressAdditional Existing Stress
• There can be other sources of existingThere can be other sources of existing stress but they can be very difficult to determinedetermine– For example bending stresses from
constructionconstruction– Usually increase estimate to account for these
stressesstresses
Subsidence StressSubsidence Stress
• Steps:Steps:– Estimate subsidence
• Depending on analysis also need curvature and• Depending on analysis also need curvature and horizontal displacement of the soil and soil strains
– Use subsidence estimate to determine stress• Simple hand calculations• Soil-pipe interaction finite element analysis
Calculate SubsidenceCalculate Subsidence
• Use standard estimation programs suchUse standard estimation programs such as Comprehensive and Integrated Subsidence Prediction (CISPM) andSubsidence Prediction (CISPM) and Surface Deformation Prediction System (SDPS)(SDPS)– Depending on the analysis need to know
subsidence horizontal soil displacement soilsubsidence, horizontal soil displacement, soil strain and curvature
Subsidence Calculation Example
-1.0
-0.5
0.0
0.004
0.006
0.008
0.010
-3.0
-2.5
-2.0
-1.5
Subs
iden
ce, f
t
-0.006
-0.004
-0.002
0.000
0.002
Soil
stra
in, i
n/in
-4.0
-3.5
-200 0 200 400 600 800 1,000 1,200 1,400 1,600
Y distance, ft
-0.010
-0.008
-200 0 200 400 600 800 1,000 1,200 1,400 1,600
Y distance, ft
Subsidence Soil strainSubsidence Soil strain
Subsidence Stress• An initial estimation of the bending strain
can be obtained from the curvature– Works for buried or exposed pipe but doesn’t
account for terrain
1.00E‐04
1.50E‐04
2.00E‐04
0.0008
0.0010
‐1.00E‐04
‐5.00E‐05
0.00E+00
5.00E‐05
Soil curvatue
, ft‐1
0.0000
0.0002
0.0004
0.0006
ng st
rain
, in/
in
‐2.00E‐04
‐1.50E‐04
‐200 0 200 400 600 800 1000 1200 1400 1600
Y distance, ft
-0 0010
-0.0008
-0.0006
-0.0004
-0.0002
Ben
din
0.0010-200 0 200 400 600 800 1,000 1,200 1,400 1,600
Y direction, ft
Finite Element ModelingFinite Element Modeling
• A better estimate of stress can beA better estimate of stress can be obtained using finite element modeling
The pipe soil interaction is modeled as– The pipe soil interaction is modeled as nonlinear springs
– Exposed pipe isExposed pipe ismodeled using contact elements for the groundcontact
A Case Study-The ProblemA Case Study The Problem
A Case Study-SubsidenceA Case Study Subsidence2
Subsidence
0
1
ft
SR3007
Horizontal displacement
SR 3007
‐3
‐2
‐1
Displacem
ent,
‐5
‐4
‐200 0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000
Distance, ft
Subsidence and Horizontal Displacement with Buried SegmentDisplacement with Buried Segment
A Case Study-FEA ModelA Case Study FEA Model
Pipe
Soil springsGround
A Case Study-ResultsA Case Study Results70,000
40 000
50,000
60,000
Buried
20 000
30,000
40,000
Stress, psi
0
10,000
20,000
abs(SL)
S equivalent
B31.8 Limit
0 500 1,000 1,500 2,000
Distance, ft
Longitudinal and equivalent stress compared with code limits
Determining Allowable StressDetermining Allowable Stress
• In most cases the allowable stress can beIn most cases the allowable stress can be determined from design codes
ASME B31 4 for hazardous liquids– ASME B31.4 for hazardous liquids– ASME B31.8 for gas
I dditi l l i f• In some cases additional analysis of pre-existing defects is required to set ll bl t l lallowable stress levels
Mitigation PlanMitigation Plan
– The recommended steps to take prior to theThe recommended steps to take prior to the subsidence
– A multi-level monitoring criterion with gappropriate responses for each level
– Inspection procedure required for the p p qmonitoring criterion
– Recommendations for post-subsidence mitigation if required
Design for SubsidenceDesign for Subsidence
• The Pipeline Research CouncilThe Pipeline Research Council International (PRCI) report entitled “Guidelines for Constructing Natural GasGuidelines for Constructing Natural Gas and Liquid Hydrocarbon Pipelines through Areas Prone to Landslide and SubsidenceAreas Prone to Landslide and Subsidence Hazards” gives a summary of state-of-the-art subsidence designart subsidence design
Some Design StrategiesSome Design Strategies
• Increase the pipeline capacity to resist ground movementground movement
• Reduce the soil loads on the pipeM dif i th i li t• Modifying the pipe alignment
BadBad
GoodGood
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