U-bend tube post bending heat treatments soaking time

[Shayan Zariean]

Dear Readers
I have bent Carbon Steel (A179) (2.11 mm Thickness) tube and there is requirement for post bending stress relief due to Sulfide stress cracking. based on UCS-56 the minimum soaking time at maximum temp. is 15 minutes, bu at UCS-79 it is mentioned that it is possible to change soaking time for less than 6 mm thickness if it is sure that all thickness is in the same temperature. so I want to know what is the soaking time for u-bend of carbon steel tube with 2.11 mm thickness? 15 minutes or lesser?
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besides i have the same question for solution annealing of Stainless Steel (SS316 and SS321) tubes with the same thickness. How much soaking time is enough for Solution Annealing of these tubes?

 

[EdStainless]

How are they heating?
Are they sure that they get uniformity?
I don't see why a couple of minutes wouldn't be enough.
Uniformity and gentle cooling will be the keys.

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P.E. Metallurgy, Plymouth Tube

 

[Dhurjati Sen]

Dear Shayan Zariean,

Is there a hardness requirement after bending stress relief for the CS tubes? If yes, then you can try a holding time of less than 15 minutes.

Else, it is 15 minutes only.

Same logic holds for the SS tubes as well.

Regards.

DHURJATI SEN
Kolkata, India

 

[Shayan Zariean]

Dear EdStainless
the heating method is in the furnace, i have proposed 2 minutes as holding time but the manufacturer emphasis on 15 minutes.

 

[EdStainless]

In a furnace you will likely need 10 min just to reach temp.
They may feel that they need that long to assure temperature uniformity.
The actual stress relief process is very fast, it is diffusion less.

When we heat SS ubends we use electrical resistance.
The heat-up and hold process is about 15-30 sec depending on the tube size.
The cool down is about 1.5-2 min.

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P.E. Metallurgy, Plymouth Tube

 

[Shayan Zariean]

Dear EdStainless
Finally , in your opinion is 2 minutes holding time (only holding step, not heating or cooling) enough for stress relief of 2.11 mm thick Carbon Steel in furnace? (2 minutes at 620 centigrade).

 

[Compositepro]

The holding time that is important is for the part temperature and not the oven temperature.