Dished Head Safety Factor

[ZaxMin]

Hi All,

If I using ASME VIII Code to calculate the 2:1 Semi Ellipsoidal Dished Head,

ASME formula calculate out the minimum thickness is 10.35mm, so do I need use the minimum thickness time the safety factor 1.2? After time safety factor will be 12.42 and I choose using plate of 15mm. If not from the min thickness 10.35mm I straight use 12mm plate.

Is there any code in ASME stated need to time the safety factor after get the minimum thickness from the formula.

Please advise.

Thanks.

C.Min

 

[victorpbr]

Where are you getting this 1.2 factor from?

Results from applying ASME formulas will give you the minimum finished thickness of the head, you must account for losses on thickness due to the fabrication process.

 

[ZaxMin]

Hi,

Which mean I need to choose using 12mm plate since the min thickness 10.35mm?

How to account for the losses on thickness on the fabrication process? Is there any formula to including it?

Thanks.

 

[JStephen]

On the thickness loss in fabrication- check with the head supplier- they should be able to tell you what nominal thickness is required to get a specified minimum thickness.

By the way, the "safety factor" (or longer more formal term for it) is generally incorporated into the allowable stresses that the code specifies, so you don't apply an additional factor for that.

 

[SnTMan]

You could also specify the head as "10.35mm (MIN)" & let the supplier worry about the thinning. Kind of a PITA nuisance not knowing the nominal thickness however.

Regards,

Mike

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

 

[chicopee]

You already have a factor of safety in the thickness calculation and that is in the allowable stress for the metal.

 

[DriveMeNuts]

Contact a head manufacturer with the diameter and minimum new thickness and they will advise you of the nominal plate thickness that they will use.

If they are really kind they might give you an "estimate" of the as formed thickness profile.