CS Tube Anealing

[Aodwan]

Hi All,

We are constructing the Heat Exchanger under ASME codes, the tubes required is of material SA179 and client wants us to perform
anealing with temp min 725, but in SA179 it depicts the heat treatment temp shall be within range of 650 or higher.

Is it needed to anealing CS tubes? Is there any where in ASTM it is mentioned?

 

[metengr]

The better approach for removing cold work and residual stresses from cold bending carbon steel is to perform a subcritical thermal treatment - similar to the temperature range of post weld heat treatment (595 deg C to 650 deg C). Your client may require a post bend treatment for service conditions. However, an anneal thermal treatment is not practical or required instead; ask the client if a subcritical thermal treatment can be used. You may need to show the benefit by a mock-up and destructive lab testing.

 

[Aodwan]

Thanks, it means after bending post weld is required, agreed.
But for plain tubes there is no need to anneal, also no where it is mentioned.

 

[metengr]

Simply because it is not mentioned in the standard does not mean it does not need to be performed. Also, you misunderstood my statement above. In lieu of annealing, I would consider a subcritical anneal (aka subcritical PWHT). All this means is that after cold bending, the bend region is heated using the same time at temperature as post weld heat treatment.

 

[Aodwan]

Yes i got your point, But for straight CS tubes where no U bending is required, do we need to annealing at Temp above 725 ?

Sorry if i misunderstood again.

 

[metengr]

No, if no cold work or welding was performed.