What is the ASTM G48 test?

What is the ASTM G48 test?

To give it it’s full title, ASTM G48 is the “Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution”. It is a corrosion test, utilising an aggressive solution of ferric chloride.

What is critical pitting temperature?

Pitting corrosion of stainless steels can be characterized by the critical pitting temperature (CPT), which is defined as the lowest temperature at which stable pitting is possible. 1 This temperature limit is defined as potential independent CPT.

How do you test for crevice corrosion?

Crevice corrosion ASTM G78 test method The test involves the application of castellated washers (MCAs) to the surface of the specimen, usually with 20 contact points on each washer in a chloride-containing environment (seawater) for a test duration of up to 30 hours (typically 24 hours).

What is critical crevice temperature?

The critical crevice temperature is the minimum temperature (°C) to produce crevice attack and CCT is usually lower than the critical pitting temperature (CPT). Computer software such as CRA-Compass can be used to assess the crevice corrosion resistance of an alloy for a given temperature and chloride concentration.

What causes intergranular corrosion?

Intergranular corrosion (IGC) It is as a result of chromium depletion, mainly due to the precipitation of chromium carbides in the grain boundaries. Chromium carbides can be precipitated if the stainless steel is sensitized in the temperature range 550–850°C (1020–1560°F), for example during heat treatment or welding.

What is intergranular corrosion test?

Intergranular Corrosion (IGC) or Intergranular Attack (IGA), is an efficient test for screening a material’s corrosion resistance under certain conditions.

How does pitting corrosion occur?

Pitting corrosion occurs when the cathode (damaged coating) is large and the anode (exposed metal) is small. Typically the surface protection layer or film becomes the cathode when it is damaged and cracked. A small area of metal is then exposed and becomes the anodic.

How does crevice corrosion occur?

Crevice corrosion occurs where stagnant solution is in contact with the metal in crevices. such as in threaded connections, beneath absorbent gaskets, and under deposits of dirt and rust.

What is ASTM G48 Method A?

ASTM G48 (Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution) [1] is a common test to evaluate the crevice corrosion resistance of stainless steels and nickel alloys.

What is the difference between pitting and crevice corrosion?

Whereas pitting corrosion occurs across the surface of a component, crevice corrosion is associated with a crevice, be that one that forms around a fastener, washer or joint, in a sharp corner or in an area where the flow of a liquid is slowed i.e. a dead spot.

How do you mitigate crevice corrosion?

Eliminating gaps, such as those found in welds and joints, can help to reduce crevice corrosion risk. Ensuring complete drainage of vessels and removing electrolytes from surfaces can further reduce risk. Utilizing solid, non-absorbent gaskets can reduce risk at connections and equipment.

How can you prevent IGC?

Intergranular corrosion can be prevented through:

  1. Use low carbon (e.g. 304L, 316L) grade of stainless steels.
  2. Use stabilized grades alloyed with titanium (for example type 321) or niobium (for example type 347). Titanium and niobium are strong carbide- formers.
  3. Use post-weld heat treatment.