Does the presence of moisture accelerate the high temperature corrosion of stainless steel?

The short answer is yes it does but the mechanism by which this occurs is complex.

The performance of stainless steels subjected to high temperature corrosion is, in general, governed the stability of the protective oxide scale that forms on the metal. To be effective, this scale should ideally be adherent to the metal, dense and stable ie it does not continue to grow. If the layer is porous or crack-prone then oxygen and / or other elements can reach the metal and the reaction continues.

There is much recorded information on the recommended maximum temperatures for stainless steels to form such protective scales in dry air when subjected to continuous exposure. Above these temperatures the oxide layer is no longer an effective barrier to the reaction taking place. Although Cr2O3, chromia, is the primary constituent of the scale for stainless steels it can be improved by the addition of other oxide formers such as silicon and aluminium.

In the presence of moisture, OH also plays a role as an oxidising species and CrO2(OH)2 forms. It evaporates readily thus removing chromium from the metal surface and reducing the potential for the formation of a protective scale. The maximum service temperature in air may be lowered by    200 deg C in the presence of moisture and if this temperature is exceeded breakaway oxidation may occur. Mitigating this risk may be possible by using alloys with higher levels of chromium and / or silicon and aluminium

>>>>>>>>>>>>>>>>>>>>are both stainless steels that are used in applications that require resistance to corrosion at elevated temperatures.

Nominal Chemical Compositions (%)

Cr Ni Si Mn N C Ce Fe
253MA UNS S30815 21.0 11.0 1.7 0.6 0.17 0.07 0.04 Bal
310S UNS S31008 25.0 20.0 0.5 1.6 0.05 Bal

Composition of an alloy will dictate is ability to resist corrosion at elevated temperatures and in the first instance this may be achieved by the formation of a dense protective scale. In the case of 310S, the nature of the protective scale is dependent primarily on the chromium whilst for 253MA the higher silicon content improves the protective scale and the cerium enhances its adhesion to the metal beneath it. Both grades have comparable resistance to oxidation.

253MA has slightly greater resistance to high temperature corrosion in the presence of sulphur containing gasses whilst 310S is better suited for nitriding / low oxygen potential environments.

The nitrogen and carbon contents of 253MA result in this grade having better creep strength properties than 310S which may be advantageous. If this is considered at the design stage it will allow for the optimisation of the thickness of the metal.

Commercially, the lower nickel content of 253MA should reflect in the price of this grade but this will only be the case when it’s compared on a like for like basis. eg it may apply for plate, a product form which is imported per sea and stocked locally in the case of both grades.


Got any questions, contact one of our sales staff

Multi Alloys specialises in the supply of high performance metal alloys in various forms. Our focus is on supplying heat and corrosion resistant metal alloys for demanding applications coupled with specialist service and advice.