geothermal operations and material science
TRANSCRIPT
Geothermal Operations and Material Science
Einar Jón Ásbjörnsson, Ph.D.
Materials Challenges in Geothermal Utilization Reykjavík University
Geothermal industry
• What is different with geothermal environment
– Geothermal brine can be oversalted, carbonated fluid with hydrogen sulfide
– Geothermal steam is sulfurous and can contain hydrochloric acid
– Cooling water can be a bacteria growing fluid
Three modes of utilizing material science
• Design
– Main parts of education in material science for engineers focuses on this part, e.g. material selection etc.
Three modes of utilizing material science
• Failure
– Basic failure analysis included in material science for engineers
What are we looking for in operation
• Corrosion
– All types of corrosion
• Wells, pipelines, pumps, separators, cooling systems, etc.
• All parameters that can affect material degradation
• Change in material properties • Brittle material due to hydrogen
Physical barriers
• There are some main factors that make material monitoring difficult in geothermal operations – Access
• Underground structures, i.e. wells
• Insulation of pipelines and equipment
• Hot surfaces
• Scaling
– High capacity factor • Few breaks in operations
Technical barriers
• Only NDT (non destructive test) are possible
– Visual (general conditions)
– Ultrasound (Thickness, cracks)
– Dye penetrant (cracks)
– Magnetic particle testing (cracks)
– X-ray (thickness, cracks)
– Eddie current (cracks)
• Mainly used for weld inspection during construction and for testing of drill components.
Methodology
• Direct methods
– Focus on one specific location
• Regular thickness measurement of a bend in steam pipe
• Indirect methods
– Focus on system stability
• Chemical analysis, pH, etc.
• Flow analysis
• Temperature in system
Direct methods
• The direct method fix on specific position – Give indications on conditions at specific point in the
system
• Interpretation is simple and action plan can be created fast. – Thinning in a bend in a well head
• Change well head or decrease velocity and continue to monitor
• Usually discrete measurements • Not possible to monitor large systems
– Risk assessment can identify critical points
Rotor inspection
• Position specific
– Visual, UT
• Action plan clear
– Use another period or change
• Low frequency
– Every x years
Indirect methods
• Focus on system as a whole – Chemical analysis
• Often continuous measuring systems
• Hard to interpret – Effects on system unknown
• pH below recommended value for a week – Action: Adjust pH in system, start deviation plan
• Action plan for deviations hard to make – System can be large
Chemical analysis
• Can provide false sense of safety – Wellhead pH does not
necessarily give indications of problems in the blending zones.
– Chemical analysis upstream in district heating system can be incorrect indicator downstream • Large complex systems with many
variables
1600 m
1000 m
• Direct methods: – NDT - Ultrasonic testing, radiography
• Indirect methods:
– Coupons test – Electrical Resistance Measurements – Linear Polarization methods – NDT - Ultrasonic testing, radiography – Hydrogen measurements – Water analysis – continuous pH and conductivity
measurements etc.
Instrumental methods for corrosion monitoring
External corrosion
• Studded PE sheet between insulation and aluminum.
– Not always used
– Critical points known
• At fixtures, outlet points
– The wetness in the insulation not monitored
• Not designed in the system
Conclusion
• One of the challenges in geothermal is to monitor material degradation during operation
• All design work (student or real life) should include a maintenance/monitoring plan. – Implementation started in applied engineering
• Risk assessments of current systems should be done in order to identify critical points for direct monitoring