Menu
Search
Filters
Close
Menu

51318-11001-The Role of Corrosion in a Mooring Chain Link Premature Fatigue Failure

Picture for The Role of Corrosion in a Mooring Chain Link Premature Fatigue Failure
Available for download

An FPSO mooring line experienced a premature chain link fracture in the top section. The subsequent examination of the failed link identified that the fracture was caused by corrosion fatigue.

Product Number: 51318-11001-SG
Author: Liangzhe (LZ) Zhang
Publication Date: 2018
Industries: Maritime , Oil and Gas Production
$0.00
$20.00
$20.00

An FPSO mooring line experienced a premature chain link fracture in the top section. The subsequent examination of the failed link identified that the fracture was caused by corrosion fatigue. The fatigue crack initiated at the bottom of a corrosion groove. The groove has a W-shaped cross-section and its bottom is located in the heat affected zones (HAZs) of the flash weld. The crack propagated radially in parallel to the fusion line of the weld and led to the final fracture when the remaining cross-section was insufficient to sustain the applied load.

The groove was approximately 64 mm long, 5 mm wide, and 2.5 mm deep at its deepest location. The metal loss at the groove was within the corrosion allowance per design standards. The corrosion groove formed most likely because of the microstructural differences between the HAZs and nearby material.

The examination also revealed severe metal loss, mainly in the form of pitting, in base metal of the link.

Some of the pits were much deeper than the corrosion groove and were at locations with higher stress concentration factors associated with the link geometry itself, i.e., stress concentration factors in the absence of corrosion. The fatigue failure occurred at the groove instead of the deep pits because the groove introduced a high stress concentration factor, which facilitated the initiation of the fatigue crack. Since the most likely cause of the corrosion groove was the microstructural differences across the weld, it appears to be reasonable to counter the specific failure mechanism by minimizing the microstructural differences though optimizing welding parameters and post weld heat treatment.

Key words: Mooring Chain Link, Corrosion, Fatigue, Design, Flash Weld

 

An FPSO mooring line experienced a premature chain link fracture in the top section. The subsequent examination of the failed link identified that the fracture was caused by corrosion fatigue. The fatigue crack initiated at the bottom of a corrosion groove. The groove has a W-shaped cross-section and its bottom is located in the heat affected zones (HAZs) of the flash weld. The crack propagated radially in parallel to the fusion line of the weld and led to the final fracture when the remaining cross-section was insufficient to sustain the applied load.

The groove was approximately 64 mm long, 5 mm wide, and 2.5 mm deep at its deepest location. The metal loss at the groove was within the corrosion allowance per design standards. The corrosion groove formed most likely because of the microstructural differences between the HAZs and nearby material.

The examination also revealed severe metal loss, mainly in the form of pitting, in base metal of the link.

Some of the pits were much deeper than the corrosion groove and were at locations with higher stress concentration factors associated with the link geometry itself, i.e., stress concentration factors in the absence of corrosion. The fatigue failure occurred at the groove instead of the deep pits because the groove introduced a high stress concentration factor, which facilitated the initiation of the fatigue crack. Since the most likely cause of the corrosion groove was the microstructural differences across the weld, it appears to be reasonable to counter the specific failure mechanism by minimizing the microstructural differences though optimizing welding parameters and post weld heat treatment.

Key words: Mooring Chain Link, Corrosion, Fatigue, Design, Flash Weld

 

Also Purchased
Picture for Comparative Evaluation of Various Types of Metallic Coatings for Structural Steel in Marine Enviroments
Available for download

51318-10912-Comparative Evaluation of Various Types of Metallic Coatings for Structural Steel in Marine Enviro

Product Number: 51318-10912-SG
Author: Oladis Troconis de Rincón / Orlando Salas / Nathalie Romero / Ivan Lasa / Matthew Duncan / Jenny Guan
Publication Date: 2018
$20.00

This paper discusses a comparative evaluation of the performance of various types of protective coatings available for the corrosion protection of structural steel components located in marine environments.
Picture for Cathodic Protection of Offshore Structures by Extreme Damage Tolerant Sacrificial Coatings
Available for download

51318-10949-Cathodic Protection of Offshore Structures by Extreme Damage Tolerant Sacrificial Coatings

Product Number: 51318-10949-SG
Author: Shiladitya Paul
Publication Date: 2018
$20.00

To explore the damage tolerance of as thermally sprayed aluminium (TSA), a coated carbon steel bar with damage was exposed to synthetic seawater.  TSA is capable of polarising the steel bar even with 90% of steel surface exposed.

 
Picture for 09066 Mooring Chains - Extent of Drain from ICCP System and Sacrificial CP System
Available for download

09066 Mooring Chains - Extent of Drain from ICCP System and Sacrificial CP System

Product Number: 51300-09066-SG
ISBN: 09066 2009 CP
Author: Lene Marita Green, Svenn Magne Wigen and Harald Osvoll
Publication Date: 2009
$20.00
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