Page 335 - Pipeline Pigging Technology

Pipeline Pigging Technology

Fig. 11. Safety margins in IP6[15] pipeline code.
An intermediate safety margin of 0.72 is obtained by using the SMYS:

'SMYS' safety margin = 0.72/1.00 = 0.72

This safety margin is arbitrary and cannot be related to the IP6 code, but
it is directly related to a pipeline property, SMYS, and is the margin resulting
from a hydrotest to 100% SMYS level. Therefore, three overall safety factors
(SM x SF) in Eqn(3) can be proposed:

(IP6)'Hydrotest' =0.8x0.97 =0.78 4(a)
'SMYS' =0.72x0.97 =0.70 4(b)
'Defect Free' =0.63x0.97 =0.61 4(c)

These safety factors are then applied to Eqns(l) and (2) to obtain a safe
operating pressure; Fig. 12 presents Eqns(l) and (2) graphically. The above
safety factors relate to the assessment methods and relevant codes; they do
not take into account detection limits, tolerances, etc.

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