PD5500 Question 1

[meca]

I am using a specification which refers to a value "m" which is defined as "Negative Slope of SN Curve from Table C.1 PD5500". I don't have a copy of PD5500, and am trying to calculate this value "m". Here is how I have calculated m:

m = -b

Log S = b * Log N + c

S - Stress Range
N - Number of Cycles
b - Slope of SN curve
c - Intercept

Can anyone that has access to PD5500 tell me if I am calculating "m" correctly?

 

[kamatr]

In Annex C of PD 5500:2000 Symbol "m" is defined as "the index in equation of fatigue design curve (see table C.1)"

Formula C-5 is of the form "Sr^m * N = A" where:
Sr = Stress Range (N/sq.mm)
m = as noted above
N = is the design curve fatigue life (cycles)
A = is the constant in equation of fatigue design curve (table C.1)

Table C.1 indicates:

For N<10^7 cycles:
Weld Class &quot;C&quot; has m=3.5 & A=4.22 x 10^13
Weld Class &quot;D&quot; has m=3 & A=1.52 x 10^12
Weld Class &quot;E&quot; has m=3 & A=1.04 x 10^12
Weld Class &quot;F&quot; has m=3 & A=6.33 x 10^11
Weld Class &quot;F2&quot; has m=3 & A=4.31 x 10^11
Weld Class &quot;G&quot; has m=3 & A=2.50 x 10^11
Weld Class &quot;W&quot; has m=3 & A=1.58 x 10^11

For N>10^7 cycles:
Weld Class &quot;C&quot; has m=5.5 & A=2.55 x 10^17
Weld Class &quot;D&quot; has m=5 & A=4.18 x 10^15
Weld Class &quot;E&quot; has m=5 & A=2.29 x 10^15
Weld Class &quot;F&quot; has m=5 & A=1.02 x 10^15
Weld Class &quot;F2&quot; has m=5 & A=5.25 x 10^14
Weld Class &quot;G&quot; has m=5 & A=2.05 x 10^14
Weld Class &quot;W&quot; has m=5 & A=9.77 x 10^13

The weld joint types are defined pictorially in Table C.2 and allow the most appropriate Weld Class to be selected to enable the fatigue analysis to be undertaken.

 

[Raydel]

PD 5500 fatigue calculations can be successfully carried out for nozzles subject to various pressure ranges using the CodeCalc programme from COADE. It takes into all the crack classifications for Types C to W inclusive. It works great.