ASME Section I - External pressure and MDMT

[ADMADM]

Dear All,

recently i have been involved in an ASME section I project and the below issues arised:

- External pressure for heads (pressure on the convex side)

- Determination of the M.D.M.T. for a given material with an assigned thickness.

For cylindrical shells a procedure consisting in 6 steps (same as per Section VIII div.1) is included in PFT para., but it for firetubes design and not for the cylindrical drum.

Does anyone have any suggestions in order to clarify the issue?

Thanks in advance.

ADMADM

[Ali366]

ADMADM,

I believe ASME It does not provide any requirement for low temperature or external pressure of the cylindrical shell.

This code applies to boilers where a low temperature is not expected either during normal operation or up-set conditions and start-up or shut-downs.

Additionally, external pressure does not usually apply to boilers. Normally there is no compressor or pump located down stream boilers which can cause a vacuum pressure. Also vacuum due to condensation (say during shut-downs or up-set conditions) is not practically possible.

So, if for any reason you need to consider additional requirements for low temperature applications, this should be included in the specification. And for external pressure design, you can still use section PFT or even ASME VIII Div.1 method, which, by concept, is essentially the same as PFT and uses the same set of external pressure charts! That sound to me a good engineering practice if you really need to consider external pressure on the shell.

Cheers,

[ADMADM]

Many thanks for your suggestions.

In anycase i will soon receive comments by AI and will post details in order to further clarify the issue.

[sharmilasu]

REFER PFT-50 & PFT-51 for external pressure calculations for tubes & furnaces.
The method is similar to Sec VIII Div 1

Regarding MDMT, this is not a design condition for boilers. To avoid brittle failure during hydrotest, Section I is specific about water temperature. It shall not be less than ambient but in no case less than 20C.