Hardness For SS-304

[adilmn]

Good morning,
There is one incident happened in our site that 2" fuel gas line (ss304) get fired due to excess temperature than allowed and need to check the integrity/micro structure change of the material through hardness.

From where can i get the brinel hardness reading for SS304?
What is the acceptable criteria for the hardness reading.
how much it can be plus/minus?

Hope any of you guys are expert in this can help to get an instant solution.

 

[nickypaliwal]

If it is sour service then the criteria is 22HRC. In general, I have not come across any SS 304 material above that hardness range.

You can check the hardness and if it is above 22HRC then need to explore more on acceptable range otherwise it should be fine.

I think hardness testing only should not be used to judge on the fitness of the material and it may have undergone microstructural change and the same should be checked.

 

[metengr]

The 304 stainless steel does not undergo any strengthening through heat treatment so using hardness to evaluate strength is not needed because the 304 stainless steel will not soften. Instead, you should perform a visual to check for distortion and perform a surface non-destructive examination using Liquid Penetrant testing to check for cracks.

 

[EdStainless]

In the annealed condition most of the specs have a max hardness of RB90.
And given that the min yield strength is only 30ksi I have seen material down at 62RB that easily passes the required strength.

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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

Also Brinel hardness of 304 does not provide relative equivalence to ultimate tensile strength as it does for ferritic steels.

 

[adilmn]

Thank you all for your valuable information.
Visual inspection and surface NDT was already done and found accepted.From the above conversation,I am understanding that there wont be any additional testing required..

 

[bobjustbob]

304 is an austenitic stainless steel. Unlike other steels it does not strengthen through heat treat. The standard heat treatment is a solution anneal, that is bringing it up to 1950°F or above followed by a water quench. Unlike other steel where the water quench refines the grain structure and creates a hard structure that requires tempering, the austenitic stainless steel remails mostly austenite with some ferrite depending on chemistry. Now, elevated temperatures can damage the structure decreasing it's corrosion resistance. If the material is heated up to 1600-850°F it can be sensitized. The carbon combines with the Chromium along the grain boundaries. The Cr is no long available to form the tenacious oxide layer protecting the metal from corrosion.

So, TL,DR, the mechanical strength of the material will not be affected but the corrosion resistance could be depending on temperature. NDE is not going to tell you it it is.