Menu
Search
Filters
Close
Menu

51315-6122-Corrosion Assisted Fatigue of an Alloy 725 (UNS-N07725) Electric Discharge Machined (EDM) Rubber Cutting Blade

Picture for Corrosion Assisted Fatigue of an Alloy 725 (UNS-N07725) Electric Discharge Machined (EDM) Rubber Cut
Available for download
Product Number: 51315-6122-SG
ISBN: 6122 2015 CP
Author: Ivan Morales
Publication Date: 2015
$0.00
$0.00
$0.00
Ivan A MoralesExxonMobil Research and Engineering2800 Decker DriveBaytown TX 77520USAABSTRACTIn 2013 an Alloy 725 (UNS-N07725) rubber cutter was found with scattered pitting after only 18 months in service which prompted additional PT inspection noticing additional cracking in section of the blade. The cracking was thought to be Chloride Stress corrosion cracking; however this failure was the first of its kind experienced within the circuit after more than 10 years of experience with this alloy in similar service. The initial material selection chose this alloy due to its high pitting and SCC resistance combined with excellent mechanical properties for which experiencing a failure in such a short time in service was completely unexpected. The branched and transgranular cracking found during the metallurgical analysis by a third party laboratory combined with the operating environment led the investigation team to propose SCC as the root cause of the failure; however since this was not consistent with our experience the other half of the fracture was requested for additional in-house analysis. Our evaluation confirmed the same branched and transgranular cracking consistent with SCC but also noticed a fatigue propagation morphology during fractography evaluation for which corrosion assisted fatigue was considered as the failure mode but the initiation of the cracking was still not fully understood. Subsequent discussions with the subsidiary about the fabrication steps highlighted a fundamental difference with other blades in the circuit. The failed component had been machined using Electric Discharge Machining (EDM) with no subsequent finishing step after the EDM. Another section of the blade with scattered pitting was then evaluated metallographically finding evidence of re-cast structure normally observed on EDM’d parts. The reduced corrosion resistance of the re-cast structure allowed the localized attack/pitting observed. The pitting acted as stress riser and allowed the nucleation of cracks that were propagated by the cyclic loads on the blade.Key words: Corrosion assisted fatigue Electric Discharge Machining EDM
Ivan A MoralesExxonMobil Research and Engineering2800 Decker DriveBaytown TX 77520USAABSTRACTIn 2013 an Alloy 725 (UNS-N07725) rubber cutter was found with scattered pitting after only 18 months in service which prompted additional PT inspection noticing additional cracking in section of the blade. The cracking was thought to be Chloride Stress corrosion cracking; however this failure was the first of its kind experienced within the circuit after more than 10 years of experience with this alloy in similar service. The initial material selection chose this alloy due to its high pitting and SCC resistance combined with excellent mechanical properties for which experiencing a failure in such a short time in service was completely unexpected. The branched and transgranular cracking found during the metallurgical analysis by a third party laboratory combined with the operating environment led the investigation team to propose SCC as the root cause of the failure; however since this was not consistent with our experience the other half of the fracture was requested for additional in-house analysis. Our evaluation confirmed the same branched and transgranular cracking consistent with SCC but also noticed a fatigue propagation morphology during fractography evaluation for which corrosion assisted fatigue was considered as the failure mode but the initiation of the cracking was still not fully understood. Subsequent discussions with the subsidiary about the fabrication steps highlighted a fundamental difference with other blades in the circuit. The failed component had been machined using Electric Discharge Machining (EDM) with no subsequent finishing step after the EDM. Another section of the blade with scattered pitting was then evaluated metallographically finding evidence of re-cast structure normally observed on EDM’d parts. The reduced corrosion resistance of the re-cast structure allowed the localized attack/pitting observed. The pitting acted as stress riser and allowed the nucleation of cracks that were propagated by the cyclic loads on the blade.Key words: Corrosion assisted fatigue Electric Discharge Machining EDM
Product tags
Also Purchased
Picture for Don’t Just Blame the SRBs and APBs for MIC
Available for download

51315-6083-Don’t Just Blame the SRBs and APBs for MIC

Product Number: 51315-6083-SG
ISBN: 6083 2015 CP
Author: Brett Geissler
Publication Date: 2015
$20.00

Microbiologically influenced corrosion has been attributed to the activity of sulfate reducing and acid producing bacteria. Advances in DNA isolation and sequencing have revealed that these classes of bacteria often represent only a small portion of the corrosive microbial population present in the oil and gas environment.
Picture for Corrosion of Carbon Steel in Biodiesel/Seawater Mixtures—A Study Related to the Corrosion of Fuel St
Available for download

51315-6095-Corrosion of Carbon Steel in Biodiesel/Seawater Mixtures—A Study Related to the Corrosion of Fuel Storage Tanks in Ships

Product Number: 51315-6095-SG
ISBN: 6095 2015 CP
Author: Shengxi Li
Publication Date: 2015
$0.00
Picture for Accelerated Corrosion Study of Direct-Fixation Fasteners
Available for download

51315-6133-Accelerated Corrosion Study of Direct-Fixation Fasteners

Product Number: 51315-6133-SG
ISBN: 6133 2015 CP
Author: Jonah Kurth
Publication Date: 2015
$0.00
Categories
Industry
Recently viewed
Popular tags
View all

Association for Materials Protection and Performance

© AMPP All Rights Reserved.
Membership Terms of Content Use
Contact Customer Support