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API 571 Damage Mechanisms general mechanical and metallurgical failure
- 1. API 571 DamageMechanisms GENERAL MECHANICAL AND METALLUGICAL FAILURE MECHANISMS
- 2. Graphitization Strain AgingBrittle Fracture A change in the carbide phase of C/S and 0.5 Mo steels after long term exposure to 800° F (427° C) to 1100°F (593° C) temperatures causing decomposition into graphite nodules. The deformation and aging at an intermediate temperature of older C/S and C-0- 5 Mo low alloy steels. Rapid fracture under stress with little evidence of plastic deformation.
- 3. Short Term Overheating ThermalShock Softening (Spheroidization) Localized overheating causing deformation and/or rupture at low stress levels. Occurs when high and non-uniform thermal stresses develop over a short period of time. If restrained, stresses above the yield strength can occur. A change in the microstructure of steels where the carbide phase change from normal plate like forms to spheroidal in the temperature range of 850°F (454°C) to 1400°F (760°C)
- 4. 885 Embrittlement Creep/ Stress Rupture SteamBlanketing A loss of toughness in alloys containing a ferrite phase (400 series SS, duplex SS, wrought and cast SS, welds & overlay) due to exposure to 600°F(316°C) to 1000°F(538°C). At high temperatures metals deform under load below the yield stress. A steam blanket inside a tube caused by a "departure from nucleate boiling" that causes localized overheating and deformation and/or rupture.
- 5. Erosion/ Erosion Corrosion Temper Embrittlement Sigma Phase Embrittlement Theaccelerated removal of material from impacts of solids, liquids or vapors. The erosion can be increased when corrosion removes protective films or scales. A reduction in toughness in low alloy steel due to long term exposure to 650°F(343°C) to 1100°F(593°C). Equipment may fail during startup or shutdown. Brittle phase in SS due to high temp exposure of 1000°F (538°C)to 1750°F(954°C). Increased likelihood due to higher ferrite, chromium, and molybdenum content.
- 6. Thermal Fatigue Dissimilar Metal Cracking Cavitation Thermal cycling resultingin cracking from high stresses at restrained areas of equipment. Cracking in the ferritic side of a weld between a 300 series SS and a ferritic material operating at high temperature. Localized impact forces of collapsing vapor bubbles causing erosion, usually in pumps and downstream of orifices or control valves.
- 7. Mechanical Fatigue Vibration-Induced Fatigue Refractory Degradation Cracking from cyclical stresses resultingfrom mechanical loading or thermal cycling. Mechanical fatigue from dynamic loading due to vibration, water hammer, or unstable fluid flow initiating at stress risers or notches. Mechanical damage and corrosion to refractory due to thermal shock, expansion, and oxidation, sulfidation, and high temperature mechanisms.
- 8. Reheat Cracking Gaseous Oxygen-Enhanced Ignitionand Combustion Cracking most often observed in heavy wall sections due to stress relaxation from PWHT and service at elevated temperatures. Many metals are flammable in oxygen and enriched air (>25% oxygen) services even at low pressures, whereas they are non- flammable in air. The spontaneous ignition or combustion of metallic and non-metallic components can result in fires and explosions in certain oxygen-enriched gaseous environments if not properly designed, operated and maintained. Once ignited, metals and non-metals burn more vigorously with higher oxygen purity, pressure and temperature.
- 9. API 571 DamageMechanisms UNIFORM OR LOCALIZED LOSS OF THICKNESS
- 10. Galvanic Corrosion Atmospheric Corrosion Corrosion Under Insulation Electrochemical induced metalloss of dissimilar metals when joined together in a suitable electrolyte such as a moist or aqueous environment or moist soil. Corrosion from moist atmospheric conditions, more severe in marine and industrial environments. Corrosion from water trapped under insulation or fireproofing.
- 11. Cooling Water Corrosion Boiler Water Condensate Corrosion CO2Corrosion General or localized corrosion of C/S and other metals caused by dissolved salts, gases, organic compounds or microbiological activity. General corrosion and pitting in boilers and condensate return piping from dissolved oxygen and CO2. Carbonic acid from CO2 in water causing general or pitting corrosion of C/S.
- 12. Flue Gas Dew- PointCorrosion Microbiologically Induced Corrosion Soil Corrosion Sulfur and chlorine species in fuel gas with water vapor condense and form sulfurous acid, sulfuric acid, and hydrochloric acid, leading to corrosion. Corrosion from bacteria, algae, or fungi in aqueous environments especially in stagnant or low flow conditions. The deterioration of metals exposed to soils related to temperature, moisture, and oxygen availability and other variables.
- 13. Caustic Corrosion Dealloying Graphite Corrosion Corrosioneither local or general caused by caustic or alkaline salts, usually in high heat transfer conditions or high solution strengths. Preferential attack on one or more alloy constituents leaving a dealloyed often porous structure. Corrosion of the cast iron matrix of cast iron leaving corrosion products and porous graphite.
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- 15. Oxidation Sulfidation Carburization Oxygen combinedwith C/S and other alloys at high temperature creating oxide scales. Carbon absorbed into a material at elevated temperature while in contact with a carbonaceous material or carburizing environment. Carbon absorbed into a material at elevated temperature while in contact with a carbonaceous material or carburizing environment.
- 16. Decarburization Metal DustingCorrosion Fatigue The removal of carbon from mainly carbon steel at high temperatures resulting in low strength. Carburization resulting in accelerated localized pitting occurring from carburizing gasses and streams containing carbon and hydrogen. Fatigue cracking from cyclic loading and corrosion initiating from stress risers.
- 17. Caustic Stress Corrosion (Caustic Embrittlement) Fuel Ash CorrosionNitriding Surface initiated cracking of metal surfaces exposed to caustic primarily adjacent to non PWHT'ed welds. High temperature wastage of metal surfaces of fired heaters, boilers, and gas turbines from fuel gas contaminants like sulfur, sodium, potassium, and or vanadium. A hard brittle surface layer on C/S, low alloy, 300 & 400 series SS from high levels of N2 in ammonia and cyanides particularly under reducing conditions.
- 18. Chloride Stress Corrosion Cracking Ethanol Stress Corrosion Cracking SulfateStress Corrosion Cracking Surface cracks of 300 SS and some nickel alloys from tensile stress, temperature, and an aqueous chloride environment. Surface-initiated cracks caused by environmental cracking of carbon steel under the combined action of tensile stress and a fuel grade ethanol Surface initiated cracks caused by environmental cracking of copper alloys in sulfate solutions over many years. Most commonly found in heat exchanger tubes, primarily in cooling water services.
- 19. Ammonia Stress Corrosion Cracking Liquid Metal Embrittlement Hydrogen Embrittlement Aqueousammonia streams cause cracking in some copper alloys. C/S cracks in anhydrous ammonia. Cracking when certain liquid metal contacts specific alloys. Hydrogen charging of metals leading to brittle cracking. Charging can come from manufacturing, welding, or service environment.
- 20. REFINING INDUSTRY UNIFORM ORLOCALIZED LOSS ON THICKNESS PHENOMENA
- 21. Amine Corrosion Ammonium Bisulfide Corr. (AlkalineSour Water) Hydrofluoric Acid Corrosion General or localized corrosion principally on C/S in amine treating processes. Alkaline sour water corrosion in hydro processing reactor effluent streams and in alkaline sour water streams. HF acid causes high rates of general or localized corrosion with hydrogen cracking, blistering, and/or HIC/SOHIC.
- 22. Naphthenic Acid Corrosion Ammonium Chloride Corrosion Hydrochloric Acid (HCI) High temperature corrosionfrom naphthenic acid content, temperature, sulfur content, velocity and alloy composition. General or localized corrosion occurring under ammonium chloride or amine salt deposits, often without free water. Aqueous HCL causing both general and localized corrosion aggressively affects most materials.
- 23. High Temp H2/H2S Corrosion SulfuricAcid Corrosion Aqueous Organic Acid Corrosion Hydrogen in H2S streams increases high temperature sulfide corrosion above 500°F with uniform loss in thickness in hot hydro processing circuits Sulfuric acid corrodes CS both generally and locally in HAZ's especially. Very sensitive to flow rates and water concentration. Organic compounds present in some crude oils decompose in the crude furnace to form low molecular weight organic acids which condense in distillation tower overhead systems
- 24. Phenol (Carbonic Acid) Corrosion PhosphoricAcid Corrosion Sour Water Corrosion Acid solvent corrodes C/S in phenol extraction of aromatics in lube oil feed stocks. Phosphoric acid can cause pitting and localized corrosion of C/S depending on acid concentration, temperature, and contaminants (free water content). Corrosion of steel due to acidic sour water (H2S) between 4.5 and 7.0 ph.
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- 26. Amine Stress Corrosion Cracking Wet H2SDamage (Blistering) Hydrogen Stress Cracking-HF Cracking most often found at non PWHT'ed carbon steel weldments in aqueous alkanolamine service. Hydrogen blistering, Hydrogen induced cracking, Stress oriented hydrogen induced cracking, and sulfide stress corrosion cracking from hydrogen permeation of steel and low alloy steel. Cracking of C/S and low alloy steels in weld metal and HAZ's from exposure to aqueous HF acid environments.
- 27. Carbonate Stress Corrosion Cracking PolythlonicAcid Stress Corrosion Cracking Cracking adjacent to C/S welds from alkaline corrosion and tensile stress. Cracking due to sulfide scale, air, and moisture acting on sensitized austenitic SS.
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- 29. High Temp Hydrogen Attack(HTHA) Titanium Hydriding Hydrogen at high temperatures reacts with carbides to form methane which cannot diffuse through the steel and also cause a loss of strength. Hydrogen diffusing into titanium creates a brittle phase.