Fretting Corrosion | Materials And Corrosion Control - PDFYAR - Engineering Notes, Documents & Lectures

Fretting Corrosion | Materials And Corrosion Control

Damage Mechanism	Fretting Corrosion
Damage Description	Metal loss on casing occurs due to rotary contact of drill pipe with casing, riser, and other down-hole elements. Excessive metal loss could result in collapse during operation.
Damage Description	Fretting Corrosion is defined as damage occurring at the interface of two contacting surfaces, one or both being metal, subject to slight relative slip. The slip is usually oscillatory as, for example, that caused by vibration. Wear corrosion and friction oxidation are terms that have also been applied to this kind of damage. Heat exchanger tube bundles may fail due to excessive vibration or noise. The main failure mechanisms are generated by the shell side fluid that passes around and between the tubes. This fluid may be a liquid, gas or multi-phase mixture. The most severe vibration mechanism is a fluidelastic instability, which may cause tube damage after only a few hours of operation. In contrast buffeting due to flow-turbulence causes very little vibration. However, after many years of service such remorseless low level vibration will produce tube wall thinning, due to fretting, which may be unacceptable in a high-integrity heat exchanger. In corrosive service such as amine, fretting is exacerbated by corrosion, particularly for carbon steel bundles. This is much less of case for austenitic stainless steel bundles.
Affected Materials	All materials
Control Methodology	Design phase: Particular attention is given to methods for achieving good tube support/baffle arrangements that minimize vibration damage. Use thick carbon steel baffles that may be softer and anodic to the stainless steel tubes. Avoid two-phase flow that may lead to bundle vibration. Reduction of the reclaimer duty by either reducing the steam temperature via usage of a desuperheater. Reduction of the reclaimer duty by plugging large number of tubes to reduce the heat source.
Monitoring Techniques	Visual examination of bundle, particularly at tube/baffle contact areas.
Inspection Frequency	Visual examination of tube bundle at every T&I (5 years).
KPIs	Mean Time Between Failures Target = 10 years
Reference Resources (Standards/GIs/BPs)	H. G. D. Goyder, “Flow-Induced Vibration in Heat Exchangers,” Cranfield University at RMCS, Shrivenham, Swindon, UK., Institution of Chemical Engineers, Trans IChemE, Vol 80, Part A, April 2002