PD 5500 Category 3 issue with allowable stress

[MikeG7]

Dear Forum

I have a problem upderstandig the PD 5500 category 3 application. If the vessel in question is cat.3 (which means not NDT was done on welds), then the PD 5500 standard says the maximum allowable stress should be Rm/5 (where Rm is the Tensile strength). Let's say the tensile strength is around 500 MPa that means effectively I must use 100MPa.

question 1)
If a torispherical head is rolled from a plate (fairly small size e.g. 1000mm diameter) there are no welds. Does the "penalty" of Rm/5 apply?

question 2)
How does one take into account the effect of temperature on the strength of the material used in the calculations. For example, if the design temp is 0 C or 100 C or 200 C, Rm/5 is still 100 MPa! ?

Help please.
Thanks

 

[EngAddict]

Q1)
3.4.2.2 Category 3
"A welded flat end or a dished end can be treated as a category 2 component even though the circumferential seam joining it to the vessel is category 3, provided that the cylindrical flange meets the thickness requirements for the cylinder."

Q2)
When design strength is calculated based on ultimate strength the mechanical properties are relatively unaffected by temperature until somewhere between the 250-350°C range for carbon steels.

 

[MikeG7]

Hello EngAddict

A belated thanks for your informed reply, it helped!