Page 534 - Corrosion Engineering Principles and Practice

500 C h a p t e r 1 2 C o r r o s i o n a s a R i s k 501

Function PCPSH
Private PCPSH_Value
PCPSH_Value = 0.05
If COAT1 = “FBE”
PCPSH_Value = if(DIST = 1, 0.05, PCPSH_Value)
PCPSH_Value = if(DIST = 2, 0.05, PCPSH_Value)
PCPSH_Value = if(DIST = 3, 0.05, PCPSH_Value)
Cathodic PCPSH_Value = if(DIST = 4, 0.05, PCPSH_Value)
protection Endif
deficiency
If COAT1 = “EP”
PCPSH_Value = if(DIST = 1, 0.05, PCPSH_Value)
PCPSH_Value = if(DIST = 2, 0.05, PCPSH_Value)
PCPSH_Value = if(DIST = 3, 0.05, PCPSH_Value)
PCPSH_Value = if(DIST = 4, 0.05, PCPSH_Value)
Endif
If COAT1 = “AE”. or. COAT1 = “CTE”
PCPSH_Value = if(DIST = 1, 0.46, PCPSH_Value)
PCPSH_Value = if(DIST = 2, 0.56, PCPSH_Value)
Cathodic PCPSH_Value = if(DIST = 3, 0.30, PCPSH_Value)
Inadequate PCPSH_Value = if(DIST = 4, 0.55, PCPSH_Value)
C.P. potential protection Endif
shielded
If COAT1 = “PT”. or. COAT1 = “PT2”. or.;
COAT1 = “SRT”. or. COAT1 = “HHT”
PCPSH_Value = if(DIST = 1, 0.30, PCPSH_Value)
PCPSH_Value = if(DIST = 2, 0.88, PCPSH_Value)
PCPSH_Value = if(DIST = 3, 0.51, PCPSH_Value)
PCPSH_Value = if(DIST = 4, 0.79, PCPSH_Value)
Endif

Function PCPINAD
Private PCPINAD_Value
PCPINAD_Value = 0.0
PCPINAD_Value = if(DIST = 1, 0.000152, PCPINAD_Value)
PCPINAD_Value = if(DIST = 2, 0.007100, PCPINAD_Value)
PCPINAD_Value = if(DIST = 3, 0.000134, PCPINAD_Value)
PCPINAD_Value = if(DIST = 4, 0.000388, PCPINAD_Value)

FIGURE 12.12 Detailed code for the basic events leading to a natural gas
pipeline cathodic protection deficiency.

for two basic events describing the probable impact of a cathodic
protection deficiency on the pipeline network.

12.5.5 Event Tree Analysis
Event tree analysis (ETA) is a logical representation of the various events
that may be triggered by an initiating event (e.g., a component failure). It
uses branches to show the various possibilities that may arise at each
step and it is often used to relate a failure event to various consequence
models. It may also be used to quantify system-failure probabilities,
where several contributory causes can only arise sequentially in time.
Like FTA, event tree analysis is also a logic-based methodology
for identifying accident scenarios, but unlike FTA it is a “forward
thinking” method. The analysis begins with a given initiating failure