Intergranular Corrosion

When austenitic stainless steels are heated or cooled through the temperature range 425-900C (800-1650F), chromium tends to combine with carbon to form chromium carbides. The carbides precipitate preferen- tially at grain boundaries depleting chromium from the adjacent areas. This reduces the corrosion resistance of the chromium depleted areas, sensitizing the alloy to Intergranular Attack (IGA). The extent of carbide formation is dependent upon time at temperature and the carbon content of the alloy. Thus, exposure in the temperature range stated does not automatically mean that sensitization, or IGA will occur.

Sensitization may also result from slow cooling from solution annealing temperatures, or stress relieving - after welding - in the 425 to 900C (800 to 1650F) temperature range. In welded fabrications, sensitization and IGA may occur in corrosive environments in a rather narrow band on either side of or on the side opposite the weld, known as the heat affected zone (HAZ).

It is important to note that even if sensitization does occur, it is not of significant consequence unless the alloy is exposed to a corrosive environment. Sensitized stainless steel performs in a normal manner and safe manner in non-corrosive applications.

Order of Resistance

904L Highest This table lists some of the common stainless steels as to general resistance to pitting or crevice corrosion in aqueous environments where corrosive conditions may exist.
317L  
329  
316/316L  
304/304L  
430  
410  
420 Lowest

Methods of Minimizing Intergranular Attack - IGA

1) Solution anneal above 1040C (1900F) followed by a rapid quench.

2) Use type 347, a Cb stabilized grade, or 321, a Ti stabilized grade.

3) Use a low carbon, 0.03% max. carbon grade such as 304L, 316L, 317L or 904L.

With today's technology, carbon is economically reduced to very low residuals. The low carbon grades are the standard for welded fabrication.

ASTM A262 practice A to E are standard tests to determine susceptibility to IGA. Practice E, the Huey test, is widely used.

 

Contact Us

If you have questions or need our depth of experience to help with your issues...

Call us: 281-556-8774

Email us: info@hghouston.com

News

The safe operation of oil refineries in the United States is under constant r...read more
When: January 30, 2017 - February 2, 2017 Where: Galveston Island Conventi...read more

View all articles

Stay Current

Sign up for our quarterly newsletter

covering updates on corrosion