pipe thicknesscalculation

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Excerpt from a nameless major oil company standard: (NOTE BOLD STATEMENTS)

Section 841.11 of B31.8 gives the hoop stress formula (Equation 400-10) relating
internal design pressure, pipe wall thickness, pipe diameter, and factors applied to
the specified minimum yield strength (SMYS) to establish a pipe stress value.

t = P·D/(2S·F·E·T) Eq. 400-10

where:
P = design pressure, psig
D = nominal outside diameter, in.
t = nominal wall thickness, in.
S = specified minimum yield strength (SMYS), psi, stipulated in the Specifications to the manufacturer
F = construction type design factor per Code B31.8 Table 841.1A, ranging from 0.72 to 0.40, for four construction types, determined from Tables 841.15A, .15B, and .15C, and Sections 841.122 and 841.123. In setting the values for F, due consideration has been given and allowance has been made for the various under thickness tolerances provided for in the specifications approved by Code B31.8
E = longitudinal joint factor per Code B31.8 Table 841.1B. For pipe normally considered for new lines, E=1.0

T = temperature derating factor per Code B31.8 Table 841.1C. For temperatures of 250°For less, T=1.0

Although mill tests for particular runs of pipe may indicate actual minimum yield
strength values higher than the SMYS, in no case where Code B31.8 refers to
SMYS shall a higher value be used in establishing the allowable stress value (see Section 841.121(f) of Code B31.8).

Code B31.8 Section 841.121(d) warns that the minimum thickness, t, required for pressure containment by Equation 400-10 may not be adequate to withstand transporting and handling during construction, the weight of water during testing, and soil loading and other secondary loads during operation, or to meet welding requirements. Table 841.121(d) gives least nominal wall thickness for all sizes through NPS 64, but Company practice is more conservative. Code B31.8 Section 816 requires pipe with a D/t ratio of 70 or more to be loaded in accordance with API RP 5L1 for rail transport, API RP 5L5 for marine, or API RP 5L6 for inland waterway. If it is impossible to establish that transporting has been done in accordance with the appropriate recommended practice, special hydrostatic testing must be done.

Code B31.8 makes no specific reference to internal corrosion allowance, but Section
863 in Chapter VI, Corrosion Control, discusses internal corrosion control in general.

Code B31.8 Section 841.121(b) limits the design pressure P for pipe not furnished
to specifications listed in the Code or for which the SMYS was not determined in accordance with Section 811.253 of the Code. Section 841.121(e) covers allowable
stress for cold-worked pipe that has subsequently been heated to 900°F for any
period of time or over 600°F for more than one hour.

Section 841.13 of the Code B31.8 covers protection of pipelines from hazards such
as washouts, floods, unstable soil, landslides, installation in areas normally underwater or subject to flooding, submarine crossings, spans, and trestle and bridge
crossings.

with above reference shall i calculate the MAOP putting the minimum value of (t) in the formula..... please guide me and do reply as early as possible