Steels_ Metallurgy and Applications, Third Edition

190 Steels: Metallurgy and Applications

2.00

1.75

~- ..,. 1.50

~1.25

e-

~2 ~.oo

0.75

0.50

0.25

Seamless

ERW

16"

42'

Spiral-SAW

26"

UOE-SAW

64"

l

80"

4 8 12 16 20 30 40 50 60 70 80

Outside diameter (in)

Figure 2.23 Size ranges available with main Japanese linepipe manufacturing processes
(After Nara et al. 32)

thermomechanical processing and therefore a wide range of compositions is used
to satisfy the property requirements of individual grades within the API speci-
fication. Sage 33 has produced a useful guide to the types of composition used
for linepipe and this is shown in Figure 2.24. It will be noted that this chart
differentiates between steels that exhibit the Bauschinger effect and those that
experience a slight increase in yield strength during pipe making. The detailed
chemical compositions used in various countries to satisfy API requirements
are illustrated in Table 2.19. This includes some very low carbon, boron-treated
steels 34 which develop a bainitic microstructure. In the production of these steels,
the slab reheating temperature is in the range 1000-1150~ and the presence of
fine particles of TiN inhibit austenite grain growth. The steels are finished at a
temperature of about 700*C.
In general, X60 grade is satisfied by controlled-rolled ferrite-pearlite steels
containing about 0.03% Nb. For X65 and X70, it is usual to supplement the
grain-refining effect of niobium with dispersion strengthening from vanadium,
and steels 3 and 5 in Table 2.19 are typical of this practice. In order to achieve
X80 properties, small additions of nickel or molybdenum are made to the Nb-V
steels and the steels are also subjected to a very severe controlled-rolling practice.

Pipeline ratings

Pipelines use a variety of fittings, such as valves, bends and tees, which have
the same property requirements as linepipe, namely high strength, toughness and
weldability. However, because of their method of production, the development
of higher strengths in fittings has tended to lag behind that in linepipe material,
which relies heavily on thermomechanical processing for the achievement of
properties. Fittings are produced from forgings or as fabrications from plate and,