Embed Size (px)
DESCRIPTION
Metallography
Citation preview
AITIS In-Situ Metallography & Replica Services
2012
ABDALLAH I. AL TAMIMI INDUSTRIAL SERVICES ESTABLISHMENT
Testing & Inspection Works
A. I. Al Tamimi Industrial Services
Metallography:
Metallography or microscopy consists of microscopic study of the structural constituents (i.e. Ferrite, Pearlite, Carbide, Austenite, etc.) of metals or an alloy by optical microscope or an electron microscope. In metallography, we also study the relation of structure to properties of metals or alloys. When metallography carried out nondestructively and at the site without destroying the component it is known as in-situ metallography.
History:
In 1860 Henery-Clifton Sorby developed a technique for the systematic examination of metals or alloys under the microscope and can therefore lay claim to be the founder of that branch of the metallurgy known as microscopical metallography.
Scope:
Field Metallography is most important NDT technique for assessment of plant health and life to avoid disastrous failures and to guarantee safe operations of critical equipments in petrochemical plants, power plants, cement plants, fertilizer plants, etc.
When material or component used in service for long time or at high temperature or high pressure its microstructure degrade or change. On-site or field metallography can be useful for assessment of in-service degradation of microstructure.
Properties like mechanical, physical, metallurgical and corrosion resistance of metals and alloys all depend on the microstructure of the metals or alloys. Advantages:
The technique is portable and can be used on-site. Field metallography can also be used to monitor quality of purchased components. Field metallography can be used to monitor the evolution of microstructural changes in
components during lifetime. This is particularly useful in assessing creep damage in elevated temperature components
(turbine rotor /discs, steam piping, heat exchanger, chemical reactor, pressure vessels, etc.) The technique can be applied to a wide variety of materials. Field metallography can complement nondestructive techniques such as ultrasonic testing.
IN-SITU OR FIELD METALLOGRAPHY
Applications:
AITIS provides On-site OR Field Metallography services on the following: Metallographic examination of various metals & alloys in different forms such as castings,
forgings, pipes, plates etc. non-destructively & at site. Life assessment of equipment & components in service at high temperature & under high stress /
pressure (like reactors, furnace tubes, turbine shaft, turbine discs, gas pipe lines etc.) Failure analysis by fracture examination. Inter-Granular Corrosion Cracking – IGCC. Cost effectiveness of heat treatment procedures on multi-sectional parts by test on each section
without cutting. Checking welds & Heat affected zone for micro cracks, creep voids & other defects in pipelines
& pressure vessels. Heater Tubes Boiler Tubes Steam Piping Tanks
In-Situ Metallography
The in-situ metallography technique consists of Location selection, Mechanical grinding, Mechanical polishing/electrolytic polishing, Chemical etching/electrolytic etching, Microscopic examination (Capture Micrograph), and Replication.
Equipments used for in-situ metallography are below Fine Grinder & Polisher with a flexible shaft & variable speed / constant torque control Electrolytic Polishing & Etching Equipment Portable Microscope (Magnification 100X – 400X) Digital Camera attached with portable microscope and captured micrograph at site. Replica Kit
Consumables used for in-situ metallography are listed below Grinding papers of different grit sizes Polishing cloths Diamond Paste Etchants (solvents) Water bottles Replica films
Damage Mechanism and Degradation of Microstructure
Degradation of microstructures determines through Field metallography or In-situ metallography:
1. Creep damage 2. Hydrogen attack 3. Thermal fatigue 4. Intergranular corrosion 5. Stress Corrosion Cracking 6. Sigma Phase 7. High temperature oxidation
8. Carburization 9. Decarburization 10. Carbide precipitation 11. Graphitization
1. Creep Damage
Creep is time dependent permanent deformation that occurs under stress at elevated temperature. The rate of this creep is a role of the material properties, exposure time, exposure temperature and the applied structural load. Generally creep occurs in furnace tubes, heater tubes, boiler tubes, turbine blades, turbine discs, reactors and other high temperature equipments use in petrochemical, Power plants, fertilizers plants etc. 2. Hydrogen Embrittlement The process in which metal become brittle due to hydrogen dissolve in metals in atomic form and make Hydrogen molecules in voids. 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). Hydrogen diffuses in metal at elevated temperature. 3. Thermal fatigue Fracture of material under cycling load is called fatigue, when fatigue is subjected to elevated and cyclic temperature is known as thermal fatigue. It is prominent in turbines where some heating or cooling takes place each time a power setting is changed. 4. Intergranular Corrosion Intergranular corrosion (IGC) OR intergranular attack (IGA) is a form of corrosion in which grain boundaries of the material are crude due to depletion of some elements from grain boundaries, like depletion of chromium in stainless steel this process is called sensitization.
5. Stress Corrosion Cracking The process of cracking metals due to corrosion, residual stresses and applied stresses. Stress Corrosion Cracking (SCC) depends on the material properties, environment that causes SCC for that material, and sufficient tensile stress to induce SCC. 6. Sigma Phase Sigma phase is a brittle, non-magnetic intermetallic phase composed mainly of iron and chromium which forms in ferritic and austenitic stainless steels during exposure at 560º-980ºC (1,050º-1,800ºF). It causes loss of ductility and toughness. It is secondary phase and form at the grain boundaries. 7. High Temperature Oxidation In high oxidation atmosphere at high temperature the oxygen penetrate inside and make the grain boundaries thicker in carbon steel. 8. Carburization Under highly carbon atmosphere and at elevated temperature the carbon is diffuses in the metals surface and make the surface hard and abrasion resistance this phenomenon is called carburization. But because too great a concentration of carbon makes metal brittle and unworkable, carburization depend on time, temperature and concentration of carbon in atmosphere. 9. Decarburization Removal of carbon from the surface of steel in presence of oxygen at elevated temperature is called decarburization. Decarburization is the opposite of carburization. When carbon is removed from the surface it becomes soft. 10. Carbide Precipitation Precipitation of alloying elements like Carbon on the grain boundaries of steel or other alloys is called carbide precipitation. Precipitation reduces the corrosion resistance and makes the steel brittle. This degradation of structure is common in stainless steel and super alloys. 11. Graphitization In solid state transformation of non graphitic carbon (carbide and solid solution) to graphite form is called graphitization. When plain carbon steel is used for prolonged time at elevated temperature the pearlite convert to graphite and reduce the strength of steel.
Location Map Contacts
Abdallah I. Al Tamimi Industrial Services Establishment
POBOX 30844 LOT 121-123 ALFAIHA INDUSTRIAL CITY AL KHOBAR, 31952, SAUDI ARABIA TEL: 966 3 864 0369 FAX: 966 3 864 0396
Email: [email protected]
Site: www.tamimiservices.com
Dhib Al Subaii Executive Manager Mobile: +966 505 824 942 Email: [email protected] Gopikrishnan.T Business Development Engineer Mobile: +966 500 566 806 Email: [email protected]
Sultan Al harthi Operation Manager Mobile: +966 502 572 227, +966 557 587 772 Email: [email protected]
