API 571 Damage Mechanisms
GENERAL MECHANICAL AND METALLUGICAL METALLUGICAL FAILURE MECHANISMS MECHANISMS
Graphitization Graphitization
A change in the carbide phase of C/S and 0.5 Mo steels after long term exposure to 800° F to 1100°F temperatures temperatures causing decomposition into graphite nodules.
Strain Aging
The deformation and aging at an intermediate temperature temperature of older C/S and C-0-5 Mo low alloy steels.
Brittle Fracture
Rapid fracture under stress with little evidence of plastic deformation.
Short Term Overheating
Localized overheating causing deformation and/or rupture at low stress levels.
Thermal Shock
Occurs when high and non-uniform thermal stresses develop over a short period of time. If restrained, stresses above the yield strength can occur.
Softening (Spheroidization)
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 to 1400°F
885 Embrittlement
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 to 1000°F.
Creep/ Stress Rupture
At high temperatures metals deform under load below the yield stress.
Steam Blanketing
A steam blanket inside a tube caused by a "departure from nucleate boiling" that causes localized overheating and deformation and/or rupture.
Erosion/ Erosion Corrosion
Temper Embrittlement
Sigma Phase Embrittlement
The accelerated 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 to 1100°F. Equipment may fail during startup or shutdown.
Brittle phase in SS due to high temp exposure of 1000°F to 1750°F. Increased likelihood due to higher ferrite, chromium, and molybdenum content.
Thermal Fatigue
Dissimilar Metal Cracking
Cavitation
Thermal cycling resulting in 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.
Mechanical Fatigue
Vibration-Induced Fatigue
Cracking from cyclical stresses resulting from 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.
Refractory Degradation
Mechanical damage and corrosion to refractory due to thermal shock, expansion, and oxidation, sulfidation, and high temperature mechanisms.
Reheat Cracking
Cracking most often observed in heavy wall sections due to stress relaxation from PWHT and service at elevated temperatures.
Gaseous Oxygen-Enhanced Ignition and Combustion Many metals are flammable in oxygen and enriched air (>25% oxygen) services even at low pressures, whereas they are nonflammable 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.
API 571 Damage Mechanisms
UNIFORM OR LOCALIZED LOSS OF THICKNESS
Galvanic Corrosion
Atmospheric Corrosion
Electrochemical induced metal loss of dissimilar metals when oined 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 Under Insulation Corrosion from water trapped under insulation or fireproofing.
Cooling Water Corrosion
General or localized corrosion of C/S and other metals caused by dissolved salts, gases, organic compounds or microbiological activity.
Boiler Water Condensate Corrosion General corrosion and pitting in boilers and condensate return piping from dissolved oxygen and CO2.
CO2 Corrosion
Carbonic acid from CO2 in water causing general or pitting corrosion of C/S.
Flue Gas DewPoint Corrosion
Microbiologically Induced 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.
Soil Corrosion
The deterioration of metals exposed to soils related to temperature, moisture, and oxygen availability and other variables.
Caustic Corrosion Corrosion either local or general caused by caustic or alkaline salts, usually in high heat transfer conditions or high solution strengths.
Dealloying
Graphite Corrosion
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.
HIGH TEMPERATURE CORROSION (400°F)
Oxidation
Oxygen combined with C/S and other alloys at high temperature creating oxide scales.
Sulfidation
Carburization
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.
Decarburization
Metal Dusting
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.
Corrosion Fatigue Fatigue cracking from cyclic loading and corrosion initiating from stress risers.
Caustic Stress Corrosion (Caustic Embrittlement) Surface initiated cracking of metal surfaces exposed to caustic primarily adjacent to non PWHT'ed welds.
Fuel Ash Corrosion
High temperature wastage of metal surfaces of fired heaters, boilers, and gas turbines from fuel gas contaminants like sulfur, sodium, potassium, and or vanadium.
Nitriding
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.
Chloride Stress Corrosion Cracking Surface cracks of 300 SS and some nickel alloys from tensile stress, temperature, and an aqueous chloride environment.
Ethanol Stress Corrosion Cracking
Sulfate Stress Corrosion Cracking
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.
Ammonia Stress Corrosion Cracking Aqueous ammonia streams cause cracking in some copper alloys. C/S cracks in anhydrous ammonia.
Liquid Metal Embrittlement
Cracking when certain liquid metal contacts specific alloys.
Hydrogen Embrittlement
Hydrogen charging of metals leading to brittle cracking. Charging can come from manufacturing, welding, or service environment.
REFINING INDUSTRY UNIFORM OR LOCALIZED LOSS ON THICKNESS PHENOMENA
Amine Corrosion
General or localized corrosion principally on C/S in amine treating processes.
Ammonium Bisulfide Corr. (Alkaline Sour Water) Alkaline sour water corrosion in hydro processing reactor effluent streams and in alkaline sour water streams.
Hydrofluoric Acid Corrosion
HF acid causes high rates of general or localized corrosion with hydrogen cracking, blistering, and/or HIC/SOHIC.
Naphthenic Acid Corrosion
Ammonium Chloride Corrosion
High temperature corrosion from 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.
Hydrochloric Acid (HCI)
Aqueous HCL causing both general and localized corrosion aggressively affects most materials.
High Temp H2/H2S 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 Corrosion Sulfuric acid corrodes CS both generally and locally in HAZ's especially. Very sensitive to flow rates and water concentration.
Aqueous Organic Acid Corrosion 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
Phenol (Carbonic Acid) Corrosion
Phosphoric Acid 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).
Sour Water Corrosion Corrosion of steel due to acidic sour water (H2S) between 4.5 and 7.0 ph.
Environment-Assisted Cracking
Amine Stress Corrosion Cracking Cracking most often found at non PWHT'ed carbon steel weldments in aqueous alkanolamine service.
Wet H2S Damage (Blistering)
Hydrogen Stress Cracking-HF
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.
Carbonate Stress Corrosion Cracking
Cracking adjacent to C/S welds from alkaline corrosion and tensile stress.
Polythlonic Acid Stress Corrosion Cracking Cracking due to sulfide scale, air, and moisture acting on sensitized austenitic SS.
Other Damage Mechanisms
High Temp Hydrogen Attack (HTHA) Hydrogen at high temperatures reacts with carbides to form methane which cannot diffuse through the steel and also cause a loss of strength.
Titanium Hydriding
Hydrogen diffusing into titanium creates a brittle phase.
