IGC in Stainless Steel.pptx

Intergranular Corrosion in Stainless Steel

1. INTERGRANULAR CORROSION BY DEENAANIRUTH S

2. There are many types of corrosion damage such as uniform corrosion, pitting corrosion that are visible to the naked eye. Whereas intergranular corrosion(IGC) is not visible. General

3. Intergranular Corrosion (IGC) sometimes referred to as Intergranular Attack (IGA), is a form of localized by preferential corrosion at grain boundaries or areas adjacent to them, with little or negligible attack on the grains. Although metal loss is minimal, IGC can cause the catastrophic failure of equipment. It attack on alloys in the presence of corrosive media that result in the loss of strength and ductility. What is IGC?

4. One should not mistake IGC with Stress Corrosion Cracking(SCC). The pictorial representation of IGC is shown below,

5. Unlike many forms of  stainless steel corrosion , intergranular corrosion occurs at a microscopic level -- impacting the very structure of the metal without always showing a sign of attack on the surface. Fortunately, an intergranular attack requires specific circumstances to occur and, in some cases, the damage is reversible.  IGC : An invisible attack on “STAINLESS STEEL”

6. Stainless steel, like many other metals and alloys, is composed of a crystallite structure.  This means the metal itself is composed of grains of various sizes. Where these grains meet are called the grain boundaries. Also known as weld decay, intergranular corrosion attacks these boundaries, causing damage to the metal at a molecular level.  Cracking and grain loss can occur, leading to reduced structural integrity, ability to withstand pressure, and further encouraging additional corrosion.

7. Much like  stress corrosion cracking , this can occur with little to no visual indication of a corrosive attack.  As such, not accounting for intergranular corrosion risks can lead to catastrophic failure of impacted piping processes and stainless steel components.

8. Intergranular corrosion occurs when certain metals and alloys reach temperatures between 425°C and 870°C (887°F to 1598°F.)  These temperatures are most common during  welding , heat treatment, or operation in high-temperature environments.  When the metal endures such extreme temperatures, it changes at a structural level.  What causes IGC?

9. Chromium present in the alloy reacts with carbon to create chromium carbide near the grain boundaries.  This carbide formation essentially converts the boundaries into anodic cells. The grain interiors then function as cathodic cells, and the intergranular corrosion begins.

10. When looking for stainless steels with excellent intergranular corrosion resistance, consider low-carbon alloys When choosing low-carbon alloys, options with carbon percentages below 0.03 percent will ensure that insufficient carbon is available for carbide formation.  If low-carbon alloys are not appropriate for your intended use, alloys with added titanium or niobium also provide exceptional intergranular corrosion resistance.  However, alloys with added titanium or niobium are susceptible to a specialized form of intergranular corrosion called a knife-line attack.  This occurs when the carbon interacts with the titanium or niobium instead of the chromium.  PREVENTING IGC DAMAGE

11. Fortunately, heat treatments can often resolve the issue and return the metal’s structure to a near-original state. In some cases, solution-annealing (also known as quench-annealing or solution-quenching) is an effective means of reversing intergranular corrosion damage in  austenitic stainless steels .  The process involves heating the metal to a temperature between 1,060°C and 1,120°C (1940°F and 2048°F.)  Once heated, the metal is water quenched, rapidly cooling it and solidifying the grain and structure. Unfortunately, the method is less than ideal for treating large assemblies. Also, it does nothing to protect pipes or other components from damage later should welding or repairs occur . Repairing IGC

12. Intergranular corrosion (also known as weld decay) affects stainless steel at the structural level and may not show visible signs of damage until corrosion has significantly progressed. Welding, improper heat treatments, and exposure to temperatures between 425°C and 870°C (887°F to 1598°F) are required to initiate an intergranular attack. Choosing low-carbon alloys or alloys with added titanium or niobium can help to increase intergranular corrosion resistance. When choosing a low-carbon alloy, options with 0.03 percent carbon or lower are recommended. KEY TAKEAWAYS

13. “Death is not greatest loss in life. The greatest loss is what dies inside while still alive. NEVER SURRENDER” THANK YOU