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51314-3989-Monolithic Isolation Joints: A Possible Weak Link in Pipeline Integrity

Picture for Monolithic Isolation Joints: A Possible Weak Link in Pipeline Integrity
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Product Number: 51314-3989-SG
ISBN: 3989 2014 CP
Author: Robert Rettew
Publication Date: 2014
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$20.00
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Monolithic isolation joints provide electrical isolation between segments of linepipe.  As the name implies a monolithic isolation joint appears as a solid block.  It can seem a simple piece of equipment because it has no moving parts and is supplied fully assembled and ready to weld into the pipeline.  However a monolithic isolation joint hides an assorted mixture of components each with one or more unique ways to fail and no way to inspect the components on receipt.  In benign service the performance of isolation joints is generally forgiving.  High temperature high pressure gas service stretches their performance and demands a high degree of quality control on each component within the monolithic isolation joint.Failures of monolithic isolation joints in a sour gas field have highlighted critical areas where purchaser attention is needed:
  • Seal procurement: In multiple cases these failures have been caused by permanent compression set of o-rings and cracked energizing springs.
  • Forging and pipe traceability: In other cases excessively hard weld heat affected zones demonstrated a lack of material traceability.
  • Design flaws: The electrical isolation sheet is a possible leak path when it is used as both an isolation component and a critical sealing surface.
Monolithic isolation joints provide electrical isolation between segments of linepipe.  As the name implies a monolithic isolation joint appears as a solid block.  It can seem a simple piece of equipment because it has no moving parts and is supplied fully assembled and ready to weld into the pipeline.  However a monolithic isolation joint hides an assorted mixture of components each with one or more unique ways to fail and no way to inspect the components on receipt.  In benign service the performance of isolation joints is generally forgiving.  High temperature high pressure gas service stretches their performance and demands a high degree of quality control on each component within the monolithic isolation joint.Failures of monolithic isolation joints in a sour gas field have highlighted critical areas where purchaser attention is needed:
  • Seal procurement: In multiple cases these failures have been caused by permanent compression set of o-rings and cracked energizing springs.
  • Forging and pipe traceability: In other cases excessively hard weld heat affected zones demonstrated a lack of material traceability.
  • Design flaws: The electrical isolation sheet is a possible leak path when it is used as both an isolation component and a critical sealing surface.
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The monolithic isolation joint is a sealed system, which obscures the individual components inside. How does one perform due diligence on a sealed, discrete system to ensure it will serve well over the asset lifecycle? We will set out a 5 section regimen.
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Risks of stray current corrosion in pipelines with isolation joints have been investigated. Both subsea pipelines with cathodic protection with sacrificial anodes and onshore above ground installation without cathodic protection are examined.
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