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Low hardness at weldment and HAZ

Low hardness at weldment and HAZ

Low hardness at weldment and HAZ

What should we do if we find low hardness of fired heater tube? I have no information during fabrication. This might be occured several years ago without thickness measurement.

For further comment, please advise me about documents to study about replica in detail.

RE: Low hardness at weldment and HAZ

Low hardness in fired tubes is not uncommon, the firing process anneals the tube and if its a welded in application the heat affected zone will be annealed from the welding.

RE: Low hardness at weldment and HAZ

You have not specified the metallurgy of the tubes, nor the hardness data. Also, design/operating temperature will help in making a rough analysis. A more accurate analysis would require thorough examination, including microstructures.

RE: Low hardness at weldment and HAZ

Does the low hardness cause a problem?

RE: Low hardness at weldment and HAZ

The tube material is 5Cr-0.5Mo steel. In my understanding, less than 120 HB should not be acceptable. I think about decarburization....Can anyone advise me about some references to study about its microstructure?

I did not see any detrimental effect in past operation. This is the first time that I check hardness at such location.

RE: Low hardness at weldment and HAZ

  Quite possible that you've measured hardness of the surface, wich is decarburised. What is the indentation depth? If you have possibilty to destruct tobe - measure hardness in cross section. If you havent this possibilty - measure hardness after deeper grinding of tube surface.
  The other case is overheating or burning of this steel. If this is so - thermal heating wont restore mechanical properties.
  To find out the reason I recomend you to make microstructure testing.

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