Dehydrogenation heat treatment (DHT)

sameercnn · **Joined:** Tue Feb 08, 2011 1:39 pm **Posts:** 7

Hi,

Please let me know what is Dehydrogenation heat treatment (DHT)? And what is the difference between DHT and PWHT?

Appreciate your quick response on this.

Thanks,
Sameer

vishaltailor · **Posted:** Tue Oct 25, 2011 2:14 pm

DHT is very different from PWHT. following are some common points.
1. DHT is performed at temp. 350 to 400 degree. Holding time depend of Materail, type of Welding normally it would be inch/hour.
2. DHT is performed to remove Hydrogen from Weld metal, as temperature increase diffusivity of Hydrogen increase and therefore, trapped hydrogen get diffuse and come out.
3. it is normally performed for Low alloy steel material. Not required for Carbon steel. As, even in Carbon steel hydrogen would be trapped inside weld metal. it would not built pressure on grain boundary.
4. Therefore, in carbon steel, when it start to built pressure on grain boundary, grain boundry gets deform, therefore pressure reduce & no chance of hydrogen induced crack. However, in Low alloy steel. Hardness of weld & material in high. Therefore, Grain boundary does not difform but get's rapture. That is called Hydrogen induced Crack.
5. Therefore, to prevent Weld Metal from Hydrogen induced crack, DHT to be perfromed.

i have made it little short. Even i hope this is clear to understand.

Dehydrogenation heat treatment (DHT)

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