ASME Section I MDMT calculation

[FabianoRibeiro]

Is there a procedure in ASME Section I for MDMT calculation or should I use any other such as Section VIII?

Best regards.

 

[metengr]

FabianoRibeiro;
There is no MDMT requirement for Section I. Why? Because boilers that produce steam operate at a high enough service temperature that DBTT is not a concern for ferrous materials. Why are you even concerned with MDMT?

 

[FabianoRibeiro]

I'm concerned about brittle fracture during the hydrostatic test.

 

[metengr]

FabianoRibeiro;
You have peaked my interest. I have to presume that this is for an existing boiler, correct? If not and this is for a new boiler, Section I has very specific requirements for water temmperature for hydrostatic testing.

If this is for an existing boiler, this can be tricky and is highly dependent on original materials of construction and age of the boiler. The National Board Inspection Code provides guidance for hydrostatic testing metal temperature.

Without going into too much detail, I would recommend you increase the water temperature for hydrostatic testing to at least 70 deg F (if posssible). If the existing boiler is over 35 years old you may need to go higher in temperature. Verify your materials of construction before you do anything - for older boilers watch out for SA 212 plate steel.

 

[FabianoRibeiro]

In fact the question refers to a new boiler.

This MDMT, as you said, will not be important now because of the restrictions that the code impose. However, when I'm doing the calculation notes of the equipment, I like to include this kind of information.

The reason of that is because it can be useful in the future. For example, if the process condition changes, the operators can look at the calculation notes and see if the equipment is suitable for the service.

 

[metengr]

FabianoRibeiro;
If this is a new boiler see if there is any plate material left over from fabrication to run impact tests. Actual impact test data of the plate material will give you a starting point in addition to the material test reports (get this as well). You don't need any calcs for this critical information (if you can get it).

Here is a tip, for fitness for service regarding pressure retaining components use API 579. ASME Section VIII, Div 1 will be of no use for in service evaluation. Having the necessary information I mentioned above combined with API 579 fitness for service is all you need.