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Applying UCS-68 (b)

Applying UCS-68 (b)

Applying UCS-68 (b)

(OP)
Hello all,

I need a clarification regarding the application of UCS-68(b)
The equipment concerned here is Steam Airpreheater which basically consists of steam flowing in the tubes and air flowing across the tubes such that air is heated as it flows across the tubes.
The mechanical construction consists of Inlet and Outlet pipe manifolds to which the tubes are welded, with a U-Bend at the end.See the attached sketch for clarification.
Design conditions are as per mentioned below :
Design temp. – 290-C
Design pressure – 7 bar / FV
Required MDMT – (-) 49 C
Inlet header – 6”, Sch 80, SA 333 Gr 6 pipe
Outlet manifold – 3” Sch 80, SA 333 Gr 6 Pipe
Tube – 1” Sch 80 , SA 334 Gr 6
Corrosion allowance – 2.5 mm for Manifolds and Tubes
Since MDMT is lower than -45C, UCS-68 (b) requirements need to be checked.
Inlet and Outlet manifolds have enough excess thickness, so UCS -66 Stress ratio is well below 0.35 and hence, UCS-68 (b) is not applicable.
But, due to the application of Corrosion allowance, required thickness for tubes is just sufficient and hence, the stress ratio is more than 0.35 making application of UCS-68 (b) mandatory.
As per UCS-68 (b), PWHT is required for all welded joints if MDMT is colder than -45C and coincident ratio is > 0.35. However, this code para also provides the criteria for exemption from PWHT as per below :
a) Material is P No. 1– this condition is satisfied
b) It is impact tested at MDMT or lower temp (in this case Tubes are being impact tested at -56C, with absorbed energy values of 34J) – this condition is satisfied
c) Joints is type no. 1 , category A & B and is subject to 100% RT –
For the case under consideration, Tube to manifold joint is basically a Cat D joint, for which I donot find any mention in this clause.
So, does this mean that since only Cat A & B joints are exempt from PWHT, Manifold to Tube joints of Cat D should be stress relieved?
Or some thing else??

Am I missing something here?
Kindly help me understand.

Thanks a lot for your advice and efforts to read until this….

RE: Applying UCS-68 (b)

D2HANDLE, I tend to agree with your interpretation, PWHT is required.

I do find the SCH 80 designation for tubing a little confusing however.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Applying UCS-68 (b)

(OP)
SnTMan,

Thanks for sharing your opinion...

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