the drilling risers
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Petroleum Engineering 406 Floating Drilling Lesson 10The Drilling Riser
Lesson 10A - The Drilling RiserRiser ComponentsRiser TensioningFatigueKill/Choke LinesInspection & MaintenanceReentry
Riser system for a floating drilling rigBOPRISER JOINTSKILL AND CHOICE LINESSLIP JOINT OUTER BARRELUPPER BALL JOINTSLIP JOINT INNER BARRELRISER TENSIONLOWER BALL JOINTMudlineMarine riser = drilling riser, get returns to surface, well control, communications link
Integral Marine Riser JointsChoke and kill lines are integral with the marine riser , flanged connections; clamp, etc
Integral Marine Riser ConnectorFlanged connection - 6 bolts
NOTE: Choke and Kill Lines
O-ring type seals- inspect when running
Integral Marine Riser Connector
Marine Riser Flexible JointFlexible joint, binding from high tensile forces, inject lubricant, up to 1,500,000 lbf!
Upper Section Marine Riser System. MARINE RISER DIVERTER ASSEMBLYRISER TENSIONING LINESTELESCOPIC JOINTKILL AND CHOKE LINESFLEXIBLE JOINT
Control valveVent lineMud returnsL.P. AnnularA diverter system.Re-directs flow from rig floor to blooey line (10+), downwind, do not shut in, erosion -10E8
Figure 6-6. Vertical steel loops used for kill / choke line transition around the ball joint.
The Drilling RiserSchematic diagram of riser with imposed forcesMEAN WATER LEVELRISER ELEMENTOptimum riser tension to minimize damage to riser and wear-and-tear on tensioners, sag
Stress in riser, kipsApplied tension in riser, kipsMaximum stressMinimum stressTension in riser must be not too low and not too high. Set at 118 kips - will fluctuate 100-136 kips ~ 15%Mean tension
Riser Considerations: Riser Metallurgy is very important. Correct heat treatment is essential. 80,000 psi min. yield strength and good toughness is preferred. Preheating, welding & normalizing after welding is critical for riser integrity & long life.
Riser Considerations:No Field Welding on Riser!
Fatigue of riser cannot be measured prior to some indication of failure. Routine inspection required.
Riser Considerations:Fatigue is an embrittlement of the metal. It often starts in the vicinity of welds or other places of high stress concentration.
Fatigue is caused by cyclic loading.
Riser Inspection:Visual Inspection of the riser should occur every time the riser is run.
Check all the seals Check all the sealing areas
Riser Inspection:A complete inspection should be made annually.Dyes: Will detect cracks. To use dyes, paint must be removed.Magnetic Particle Inspection: Sand blast areas around welds prior to magnetic particle inspection.
Riser Inspection: Ultra-Sonic Inspection: May detect cracks below the surface. This test is run inside pipe. Paint removal is not necessary. X-Ray Inspection: Is for cracks inside the metal. It may miss surface cracks.*No one technique will find all the cracks.
Riser Instrumentation: Heavy Gauge: Pointer attached to guide line moving in front of graduated board.
Riser Angle Indicator (at ball joint):
Riser Instrumentation: Accurate Positioning System: For detecting and monitoring vessel position.
Ball Joint: A Ball Joint Angle > 4 degrees is an indication that something is wrong!
Vessel is offset Riser tension is inadequate
Ball Joint:Must decrease ball joint angle before operations are resumed.
Remedial Action: Decrease Offset Increase Riser Tension
Vessel to Seafloor Guidance SystemGuidelines are used for guiding equipment from the vessel to the seafloor.
Selection and care of guidelines is critical.
Vessel to Seafloor Guidance System
Guidelines should not be tensioned beyond 1/3 of breaking capacity
Butinadequate tension is the most common cause of failure in guidelines
Vessel to Seafloor Guidance SystemTension should be maximum when landing the BOP stack, or when landing the riser onto the stack.When the guidelines are not being used to run equipment, tension may be slacked off to ~ twice the weight of the line in seawater.
Table 6-1. Recommendations forConventionally Used GuidelinesAs water depth increases, larger diameter guidelines must be used.
Higher tensioning is required.
Dont forget to limit tension to < 1/3 of breaking strength.