Allowable Stress Values

[MIMAN]

Does anyone have access to the Allowable Stress Tables in ASME Sec. 2D? I am trying to locate the allowable stress for SB-168 N06600 in order to accurately calculate the Tmin. values for a pressure vessel.

 

[metengr]

Better have a service temperature.

 

[MIMAN]

Service Temp. is 400°

 

[metengr]

22.9 Ksi for plate annealed.

 

[MIMAN]

Thanks. I actually found 23.3 Ksi in ASME 2015. I have been trying to explain to some Chemical Engs. that Tmin is not simply obtained by subtracting the Corrosion allowance from the Nominal on the U1 form.

 

[SnTMan]

Well, good luck with that

Regards,

Mike

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

 

[jte]

Well, provided that one checks all of the potential governing conditions for thickness, then yes, a t[sub]min[/sub] which is a commonly used phrase (I also hear "retirement thickness"), or more precisely the "required thickness" as defined in VIII Div. 1 Appendix 3 in the entry for "thickness of vessel wall", can be calculated separately. However, depending on the jurisdiction and other legal issues, one would be wise to consider going thru an Alteration if one is "fine tuning" the corrosion allowance in a post construction environment. I've seen many hoop stress calc's scrawled into the margin of a U-1 form, sometimes even accompanied by initials and a date. Yet, the only legal document for the vessel is the U-1 form, and changing the data on that form can in many cases require a formal process, typically along the lines of an Alteration as governed by NBIC. In the admittedly rare case that a formal investigation is initiated by some government entity, having thorough documentation is a good thing.

Now, if one is performing a FFS approach, that's a bit different, though similar.

Better to have the required thickness determined in the design phase than to try to figure it out after the vessel has been in service. This is relatively easily done, and reduces the number of issues that could come up later.

 

[marty007]

t.min is great, but where is the limiting area? Have you considered nozzle reinforcement?

Often any excess material present in the shell material is utilized in the calculations for nozzle reinforcement. So, t.nom-CA is often accurate in areas around nozzles.