Fusion Bonded Epoxy Coatings (FBE) and Disbondment (7246)
By M. Zamanzadeh and Huiping Xu
Fusion Bonded Epoxy (FBE) coating has been used for corrosion protection of underground pipe lines since the 1960’s. FBE provides protection of pipeline under cathodic protection even though there may be dis-bondment or blistering. FBE does not shield cathodic protection current under normal conditions, a characteristic which likewise distinguishes FBE coating from all other coating. In this paper failure analysis methodology will be applied to the principal mechanisms by which FBE coatings fail during long term service; with specific application to case studies involving blistering.
The case studies apply standard failure analysis techniques to determine the primary causes and modes of failures. Solution in blistered areas, pH and presence of cations and chlorides on the surface and in the coating will provide evidence for surface contamination/dis-bondment mechanism. If AC interference or shielding is present, localized corrosion attack in blistered areas can be detected prior to deep penetration in to wall thickness by effective corrosion monitoring. This can be achieved by on-time monitoring of soil corrosivity and AC/DC interference by test coupons.
Keywords: Corrosion Protection, Pipeline, Coating, Fusion Bonded Epoxy Coatings (FBE), Blistering, Coating Failure Mechanism, Cathodic Protection, AC Interference, DC stray Current Corrosion,
Corrosion Risk Assessment and Failure Analysis in Industrial Water Systems – (7248)
By Mehrooz Zamanzadeh and Huiping Xu
Industrial water system components are at increasing risk of damage due to corrosion and metal loss as they get close to the end of their design life or if the system exhibits any of the following: accelerated corrosion, perforation, deposit build up (plugging), discoloration, and excessive attack due to corrosive bacteria.
The purpose of this paper is to provide failure analysis case histories on corrosivity, pitting tendency and the risk associated with corrosion activity in industrial water systems. Failure analysis methods, failure mechanisms, primary cause and sources of corrosion attack with recommendations are described at the end of each case history. Corrosion mitigation recommendations and risk ranking is based on many years of experiences and water system studies in industrial water systems.
Keywords: Corrosion Risk, Inspection, Failure Analysis, Industrial Water Systems, Corrosion Mitigation, Corrosivity, Pitting Corrosion.
Fatigue Failure Analysis Case Studies
By Mehrooz Zamanzadeh, Edward Larkin and Reza Mirshams
Fatigue fracture can occur in many components such as fasteners and tubular pole structures. In this paper, fatigue failure mechanisms have been described and the application of the principles for failure analysis for each case will be presented. Cyclic loading at stresses above the fatigue limit of the material can initiate cracks at the surface or at internal defects. Macroscopic and microscopic observations of fatigue crack initiation and approaches for characterization of fatigue failures have been described.
Two case studies present application of laboratory analysis techniques to determine primary causes and modes of failures.
Keywords: Fatigue Cracking, Fatigue Failure, Metallurgical Investigation, Fracture.
Cathodic Protection, Defective Coatings, Corrosion Pitting, Stress Corrosion Cracking and Soil Corrosivity Mapping and Corrosion Assessment in Aging Pipelines (Paper No. RISK16-8727)
By Mehrooz Zamanzadeh and Reza Mirshams
Pipelines are among the most common means used for transporting hazardous gases and liquids in the United States. However, underground pipelines are aging and are at risk of corrosion failure due to coating degradation, pitting corrosion and stress corrosion cracking. Those tasked with maintaining these pipelines require an in-depth understanding of the locations where these aging pipelines are at risk of localized corrosion attack and cracking. Corrosion failures in aging pipelines are either sudden catastrophic ruptures or gradual leaks due to localized corrosion. Many factors associated with these corrosion areas are coating failure, degradation, disbondment, blistering, delamination, mechanicalpressure and stress concentration, galvanic action, corrosive ions, the presence of moisture, corrosive soils, AC interference, inadequate cathodic protection and shielding.
These areas have a much higher statistical probability of catastrophic failure and rupture. Most of the time initiation of stress corrosion cracking (SCC) and pitting corrosion are detected by coincidence in excavation and digs and is not targeted or predicted by analysis of corrosion performance parameters. Internal or In-line inspection (ILI) tools have limited capability for detecting or identifying stress corrosion cracking and pitting corrosion initiation. Here we would like to elaborate on corrosion risk assessment based on soil corrosivity mapping in addition to procedures outlined in NACE SP 0204-2015.
Keywords: Stress Corrosion Cracking (SCC), Pitting Corrosion, Corrosion Risk Assessment, Soil Resistivity, Soil Corrosivity Mapping, Coating Disbondment and Cathodic Protection.