Page 54 - Pipelines and Risers

Wall-ihickness and Material Grade Selection 27

Table 2.1 Characteristic thickness and diameter used in various pipeline codes.

1 Code Thickness 1 Diameter
ABS (2000) Minimum mean
ASMEB31.1 (1951) Minimum external - 0.8 t,,
ASME B31.3 (1993) Minimum external, mean or
external - 0.8 t,,
ASME B31.4 (1992) Nominal external
ASME B31.8 (1992) Nominal external
BS 8010 (1993) Minimum external, close to mean for
D/t I20
CEN 234WG3-103 (1993) Minimum external
CSA-Z184-M86 (1986) Minimum external
Danish Guidelines Minimum internal
DNV (2000) Minimum mean
NEN 3650 (1992) Minimum I mean ~~ II
NPD (1990) Minimum I external II

2.3.2 Hoop Stress Criterion of DNV (2000)
The primary requirement of the pipe wall-thickness selection is to sustain stresses for pressure
containment. The tensile hoop stress is due to the difference between internal and external
pressure, and is not to exceed the permissible value as given by the following hoop stress
criterion:

where:
Oh = hoop Stress
pi = internal pressure
pe = external pressure
D = nominal outside diameter of pipe
tl = minimum wall thickness
tl = nominal wall-thickness - fabrication tolerance - corrosion allowance
SMYS = Specified Minimum Yield Stress
fy,temp = derating value due to temperature

The usage factor for pressure containment is expressed as:

(2.4)