Process Flow Diagrams (PFDs) may be accessed from a pull. -down menu or from the Solver. Damage mechanisms shown on the PFDs are hyperlinked to the . For API API exam preparation you need API pdf dumps. Corrosion and Materials. Professional braindumps can actually save your skin if you haven't. API RP provides an in-depth look at over 60 different damage mechanisms that can occur to process equipment in refineries.
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Environment Assisted Cracking 环境–辅助开裂 Environment – Assisted Cracking Chloride Stress Corrosion Cracking (Cl-SCC) Corrosion. API pdf - Download as PDF File .pdf), Text File .txt) or read online. Course Overview. API RP is the latest edition that describes damage mechanisms affecting equipment in the refining and petrochemical industries.
However, consideration should be given to the possible effects of sensitization that may occur, increasing susceptibility to polythionic SCC, possible distortion problems and potential reheat cracking. Monitor pH and ammonia of water draw samples to assess susceptibility of copper alloys. Questions and Answers material is updated in highly outclass manner on regular basis and material is released periodically and is available in testing centers with whom we are maintaining our relationship to get latest material. Rolled area is highly susceptible. Jordan India. On a microscale, the material will contain less ductile fracture surface, but must often be compared to a fracture without the presence of hydrogen.
Figure — High magnification view of a cross-section of the tube in Figure showing transgranular cracking. The CuNi and CuNi alloys are nearly immune. SCC in steam service can sometimes be controlled by preventing the ingress of air. SCC of steel can be prevented through the addition of small quantities of water to the ammonia 0. Consideration must be given to vapor spaces could have less than 0.
Weld hardness should not exceed BHN. Prevent ingress of oxygen into storage facilities.
Monitor pH and ammonia of water draw samples to assess susceptibility of copper alloys. Inspect heat exchanger tubes for cracking using EC or visual inspection. Rolled area is highly susceptible.
WFMT welds inside tanks. Cracking can be very sudden and brittle in nature. Typical combinations of industrial significance are shown in Table Very small quantities of the low melting point metal are sufficient to cause LME.
Cracking under load can be extremely rapid such that cracks may pass through the wall within seconds of contact with the molten metal. Examples include melted zinc galvanizing, cadmium electrical housings, tin or lead from solders, and melted copper components.
A common example is Series SS piping or vessels in contact with or previously rubbed against galvanized steel Figure and Figure 4- Figure Photomicrograph of a section of the elbow in Figure , illustrating Figure — Sketch of a stainless steel the intergranular nature elbow that suffered liquid metal embrittlement of zinc-filled cracks in as a result of dripping molten zinc during a fire. LME can only be confirmed through metallography by the presence of intergranular cracks, usually filled with the low melting metal.
For example, galvanized steel components should not be welded to Series SS. Hydrogen Embrittlement HE can occur during manufacturing, welding, or from services that can charge hydrogen into the steel in an aqueous, corrosive, or a gaseous environment. Welding — if wet electrodes or high moisture content flux weld electrodes are used, hydrogen can be charged into the steel delayed cracking.
Cleaning and pickling in acid solutions. Service in high temperature hydrogen gas atmospheres, molecular hydrogen dissociates to form atomic hydrogen that can diffuse into the steel. Wet H2S services or HF acid services in which atomic hydrogen diffuses into the steel.
Cyanides, arsenic and FeS can act as hydrogen recombination poisons that diminish the hydrogen gas reaction and allows for greater charging rates. Manufacturing — melting practices or manufacturing processes particularly where components are plated hydrogen flaking.
Cathodic protection. Effects decrease with increasing temperature. If the hydrogen is present and a sufficient stress is applied, failure can occur quickly. In some cases, thresholds of critical hydrogen concentrations have been established. Certain microstructures, such as untempered martensite and pearlite, are more susceptible at the same strength level than tempered martensite.
Carbon steel that is severely hydrogen charged will have lower toughness than with no hydrogen.
However, mild steel used for vessels and piping in most refining, fossil utility and process applications have low hardness and are usually not susceptible to HE except at weldments, particularly the HAZ, if suitable PWHT is not performed.
Alloys that have a tensile strength above ksi can absorb hydrogen during electroplating and crack. On a macro-scale, there is often little evidence, although some materials will appear to have brittle fracture surfaces. On a microscale, the material will contain less ductile fracture surface, but must often be compared to a fracture without the presence of hydrogen.
Cracking due to hydrogen embrittlement of a carbon steel tube. Intergranular crack emanating from surface in the tube. High magnification photomicrograph of fracture surface showing intergranular nature of cracking.
Sulfide stress cracking see 5. Hydrogen Embrittlement — Definition and Meaning When tensile stresses are applied to a hydrogen embrittled component it may fail prematurely.
Hydrogen embrittlement failures are frequently unexpected and sometimes catastrophic. An externally applied load is not required as the tensile stresses may be due to residual stresses in the material. Hydrogen Embrittlement in carbon steel, zinc plated part. The mechanism starts with lone hydrogen atoms diffusing through the metal.
At high temperatures, the elevated solubility of hydrogen allows hydrogen to diffuse into the metal or the hydrogen can diffuse in at a low temperature, assisted by a concentration gradient.
When these hydrogen atoms re-combine in minuscule voids of the metal matrix to form hydrogen molecules, they create pressure from inside the cavity they are in. This pressure can increase to levels where the metal has reduced ductility and tensile strength up to the point where it cracks open hydrogen induced cracking, or HIC. High-strength and low-alloy steels, nickel and titanium alloys are most susceptible. Dissolved oxygen and the presence of variable stresses such as cyclic stress or component flexing, increase the propensity for cracking.
Stress may be applied or residual. Highly stressed, locally cold worked components, or components with stress concentrators are susceptible to cracking. Variable stresses, such as those produced by loading and unloading of tanks, have led to cracking in tank bottoms and floating roofs. Corrosion inhibitors may be added to ethanol to prevent general corrosion in vehicle fuel systems, but their affect on SCC is not fully understood. Aeration i. Cracking has not been found under deaerated conditions.
The maximum potential for ethanol SCC occurs within a narrow range of water content between 0. Galvanic coupling of a new steel to corroded steel increases the likelihood of ethanol SCC.
Increasing the chloride content of the ethanol tends to increase the severity of cracking and changes the crack type from mainly intergranular found in the field to transgranular cracking.
All grades of carbon steel are susceptible b Cracking has also been reported in a pipeline used to transport FGE to and from a terminal.
There has been one reported failure of an end-user E tank. Field failures tend to be intergranular, while laboratory testing has produced all crack morphologies. The cracking mode appears to depend on the chloride level, with an increased chloride content tending to shift the cracking from intergranular to transgranular or mixed mode. Research to confirm this is currently under way. Some small leaks may occur before an ethanol crack can be visually detected.
Figure — Ethanol SCC in steel tank bottom.
Note crack running parallel to fillet weld in striker plate. Figure — Ethanol SCC in a steel air eliminator vessel. Note cracks running perpendicular to the weld. Figure — A leak in piping resulting from an ethanol SCC adjacent to the weld. Figure — SCC in steel pipe from a loading rack supply line. The top figure shows a 7-inches long crack parallel to the weld root on the pipe ID surface. The bottom picture is a cross-section of above crack showing initiation outside the weld heat affected zone on the pipe's inside surface Nital etch.
The top picture shows the crack parallels the pipe-to-tee circumferential weld. The bottom picture shows the inside and outside of the pipe after splitting and cleaning the weld area.
Parallel SCC cracks are clearly visible adjacent to the weld. Figure — The top picture shows cracking initiating in the base metal on the ID of a section of piping adjacent to the weld. The bottom picture is a high magnification photomicrograph of the crack above illustrating the predominately intergranular nature of the cracking. Figure — Photomicrograph of SCC in a steel tank bottom showing highly branched, intergranular cracks at X.
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