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PD5500 Question

PD5500 Question

PD5500 Question

(OP)
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?

RE: PD5500 Question

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 "C" has m=3.5 & A=4.22 x 10^13
Weld Class "D" has m=3 & A=1.52 x 10^12
Weld Class "E" has m=3 & A=1.04 x 10^12
Weld Class "F" has m=3 & A=6.33 x 10^11
Weld Class "F2" has m=3 & A=4.31 x 10^11
Weld Class "G" has m=3 & A=2.50 x 10^11
Weld Class "W" has m=3 & A=1.58 x 10^11

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

RE: PD5500 Question

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.

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