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# Calculating Nominal Design Stress (f) (BS EN 12516-2)

## Calculating Nominal Design Stress (f) (BS EN 12516-2)

(OP)
Hi,

I have been studying BS EN 12516-2 where it mentions the calculation method for steel valve shells and my question is how to calculate the "f" value for the wall thickness calculation.

There is a table (table 2) mentioning that it should be calculated regarding the steel, nevertheless I am still not sure where to take the values of Rp0,2/t, Rm, etc from.

I am looking to calculate the min wall thickness for the material ASTM A536 65-45-12. Should I consider 310Mpa / 1,9 as the value of "f"?

### RE: Calculating Nominal Design Stress (f) (BS EN 12516-2)

Hi, ASTM A536 is for iron castings. The safety factor for those is in EN 12516-4. For 12% enlargagement it should be Rp/3,5 aprox.

### RE: Calculating Nominal Design Stress (f) (BS EN 12516-2)

(OP)
@ManoloGalarraga

Thanks for your reply, EN 12516-4 does not mention this material, howcome do you know the SF should be around 3,5?

### RE: Calculating Nominal Design Stress (f) (BS EN 12516-2)

Hi, in EN 12516-4 the safety factor is related to the elongation:
- 18% or more: 2,4
- 15% or more: 3,5
- 7% and 10%: 4
- 3% or less: 5

12% is not listed but so you can choose 3,5 or 4.

By the way in EN 12516-4 there's a mistake (I think).
EN GJS 400-18: 2,4
EN GJS 400-18 LT and RT: 5
I think there's no reason for this.

### RE: Calculating Nominal Design Stress (f) (BS EN 12516-2)

(OP)
@ManoloGalarraga

I didn't know this.. thanks. By the way, where in the standard it is stated?

I am making the question because I am using the resulting "f" value to calculate the minimum wall thickness of a valve regarding BS EN 12516-2.

### RE: Calculating Nominal Design Stress (f) (BS EN 12516-2)

Hi Marcelo,
The EN 12516 is made for Steel Valves. Cast Iron is not steel and has another code. In most times also a higher test pressure (2x maximum working pressure).
The EN 12156 Part 1 is the European version of ASME B16.34. The difference is that the European Steels are tabbeled in pressure/temperature classes. Also EN 1092 flanges and ASME B16.5 and B16.47 are taken-up.

The EN 12516 Part 2 is the calculation method, old school, for steel valves (with materials given in ASME B16.34). If you like to differ from the ASME B16.34 use the proper code.

Despite the lot of reading, start with the forword in the Euopean Norms. There is most times taken-up for what the standard is made.

Cheers,
Peter

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