Corrosion Damage (Forms of Corrosion)

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Engineering Encyclopedia Saudi Aramco DeskTop Standards CORROSION DAMAGE (FORMS OF CORROSION) Note: The source of the technical material in this volume is the Professional Engineering Development Program (PEDP) of Engineering Services. Warning: The material contained in this document was developed for Saudi Aramco and is intended for the exclusive use of Saudi Aramco’s employees. Any material contained in this document which is not already in the public domain may not be copied, reproduced, so
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  Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services. Warning: The material contained in this document was developed for Saudi Aramco and is intended for the exclusive use of Saudi Aramco’s employees. Any material contained in this document which is not already in the publicdomain may not be copied, reproduced, sold, given, or disclosed to thirdparties, or otherwise used in whole, or in part, without the written permissionof the Vice President, Engineering Services, Saudi Aramco. Chapter : Corrosion For additional information on this subject, contactFile Reference: COE-101.02 PEDD Coordinator on 874-6556 Engineering Encyclopedia   Saudi Aramco DeskTop Standards CORROSION DAMAGE(FORMS OF CORROSION)  Engineering Encyclopedia Corrosion BasicsCorrosion Damage (Forms of Corrosion)Saudi Aramco DeskTop Standards i SECTION PAGE CORROSION DAMAGE (The Various Forms of Corrosion)..........................................6   Engineering Failures.................................................................................6   Corrosion Risks........................................................................................7   GENERAL CORROSION (UNIFORM METAL WASTAGE).........................................10   LOCALIZED CORROSION..........................................................................................16   Galvanic Corrosion............................................................................................16   Intergranular Attack...........................................................................................23   Sensitization and Weld Decay...........................................................................25   Exfoliation..........................................................................................................27   Pitting Corrosion................................................................................................29   CRAs/Passive Metals.............................................................................30   Pitting in Sour Service.............................................................................35   Crevice Corrosion, Under Deposit & Under Insulation Corrosion......................37   Fretting..............................................................................................................42   VELOCITY RELATED ATTACK...................................................................................44   Flow Assisted Corrosion....................................................................................46   Erosion- Corrosion.............................................................................................48   Impingement Attack...........................................................................................53   Cavitation Damage............................................................................................54   ENVIRONMENTALLY ASSISTED CRACKING...........................................................59   Stress Corrosion Cracking (SCC)......................................................................61   SCC Mechanisms...................................................................................65   Hydrogen Embrittlement (HE)............................................................................69   Hydrogen Damage Of Oil Field Equipment In Sour Service..............................72    Engineering Encyclopedia Corrosion BasicsCorrosion Damage (Forms of Corrosion)Saudi Aramco DeskTop Standards ii Sulfide Stress Cracking (SSC)...........................................................................76   Stress Orientated Hydrogen Induced Cracking (SOHIC)...................................78   Corrosion Fatigue..............................................................................................81   HIGH-TEMPERATURE DEGRADATION AND CORROSION.....................................85   High Temperature Micro-structural Changes and Embrittlement.......................86   High Temperature Oxidation..............................................................................89   Sulfidic Corrosion..............................................................................................90   Hydrogen Attack (Decarburization)....................................................................95   Carburization and Metal Dusting.......................................................................98   Hot (Molten Salt) Corrosion.............................................................................101   GLOSSARY...............................................................................................................103   LIST OF FIGURES  Figure 1 “Bath tub” Curve of Failure Rate / Hazard Function versus Age.....................7   Figure 2 General or Uniform Corrosion Mechanisms..................................................10   Figure 3 Corrosion Allowance Concept.......................................................................11   Figure 4 Predicted CO 2 Corrosion Rates [] ..................................................................12   Figure 5 General Corrosion – Field Observations.......................................................13   Figure 6 Representation of Galvanic Corrosion..........................................................16   Figure 7 Stainless Steel Fastener in a Galvanized Sheet –Lack of Insulation Washer caused AcceleratedCorrosion of Zinc Coating and Steel Substrate............................................17   Figure 8 Dissimilar Metal Couple Mechanism.............................................................18   Figure 9 Weldment Corrosion in a Condensate Line (CO 2 system)............................18   Figure 10 Area Principle for Galvanic Corrosion.........................................................21   Figure 11 Example of Design Detailing Required to Control Galvanic Corrosion........22    Engineering Encyclopedia Corrosion BasicsCorrosion Damage (Forms of Corrosion)Saudi Aramco DeskTop Standards iii Figure 12 Intergranular Corrosion of Pump Impeller...................................................24   Figure 13 End Grain Attack (Intergranular Corrosion initiated in Crevice)of Washer fabricated from 420 SS after 3 years Wash Water Duty............24   Figure 14 Representation of a Sensitized Grain Boundary in 304 Stainless Steel......25   Figure 15 Schematic Illustration of Weld Decay..........................................................26   Figure 16 Exfoliation of Rolled Aluminum Alloy Sheet.................................................27   Figure 17 Pitting Corrosion..........................................................................................29   Figure 18 Pitting of 410 SS Bubble Caps & Tray (NGL stripper column), Typical of Pit Morphology on Stainless Steels and CRAs Exposed to Cl - & H 2 S,........30   Figure 19 Polarization Curve of 304 SS in a Chloride Containing Solution showingPassivation, Film Breakdown Transients and the Pitting Potential.............31   Figure 20 Electrochemical Noise Transients from Pitting Events................................33   Figure 21 Resistance to Pitting & Crevice Corrosion with Alloying Additions..............34   Figure 22 Corrosion Pit in C-Steel in a Sour System...................................................35   Figure 23 Crevice Corrosion under a Gasket between Water Box and End Plate......37   Figure 24 Initial Stage in the Development of Crevice Corrosion between Two Bolted Plates...........................................39   Figure 25 Later Stages of Crevice Corrosion – Concentration Cell.............................40   Figure 26. Perforation of Web of Pipe Bridge Support due to Corrosionunder Fire Protection Insulation (a form of crevice corrosion).....................41   Figure 27 Fretting Between Two Surfaces..................................................................43   Figure 28 Effect of Fluid Flow on Rates of General Corrosion....................................47   Figure 29 Representation of Erosion-Corrosion..........................................................48   Figure 30 Erosion-Corrosion of a Copper Alloy Tube, Seawater Cooling....................49   Figure 31 CO 2 “Mesa” Corrosion - a form of Erosion-Corrosion..................................49   Figure 32 Increased Metal loss due to Erosion Corrosion...........................................51   Figure 33 Erosion-Corrosion of CRAs in a Choke valve Well Test..............................52   Figure 34 Impingement Attack....................................................................................53  
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