Pressure vessel with cladding

[zdji1969]

Hi everybody,
We are preparing details for the fabrication of 2 pressure vessels (Separators) with the following requirements written on the datasheet:
- Code: ASME VIII Div. 1
- Base material: SA-516 Gr.70 (thk. 42 mm) with internal cladding Duplex 2205 (UNS S32205) according to SA-264
- The cladding is intended for corrosion protection
- PWHT is required
- Dimensions: ID = 5250 mm, Tan-Tan = 20000 mm

1. Our sub-contractor would like to apply weld overlay on the whole vessel not only on attachments (nozzles, manways, etc) while the cladding is specified (especially for shell & heads); is this acceptable?
2. The problem of precipitation may occur (Duplex cladding); what precautions must he take to avoid the problem?
3. We understand the UCL part of the code is not applicable as the cladding is an anti-corrosion; is that right?
4. Special question: if we would like to avoid PWHT by reducing the base material thickness, what material can we use in substitution of the proposed SA-516 Gr. 70? is that feasible as per ASME VIII?
5. If we use ASME VIII div.2 instead of Div.1, may we have a thickness reduction?

Thanks in advance for your help

 

[gr2vessels]

Weld overlay on the entire wetted area is very common, the welding procedures are also common. Your specification has to include the minimum unmodified 2205 material, which usually stands at 3-3.5 mm plus 1.5 mm max thickness of the intermetallic weld metal. Depending on the weld overlay process and the maximum required overlay thickness, you can cladd everything, including nozzles, size permitting.
To reduce the thickness by 25% you might need to reduce the design conditions or use better (more expensive) materials. For example, if money is not object, you might make the whole thing out of Duplex material and the shell thickness will drop significantly. Also, no more PWHT!
A high pressure separator is quite commonly designed per ASME VIII-2. However, I wouldn't consider 1.5-2 MPa high pressure. What you might save on the material thickness will be spent on inspection requirements of Div. 2.
Cheers,
gr2vessels

 

[mechyp]

Hi Zdji1969

For thickness reduction you can check Material grade SA 387 Cl2 grades.

regards
mechyp