Steels_ Metallurgy and Applications, Third Edition

Low-carbon structural steels 187

Apart from differences in nomenclature for yield strength and formula presenta-
tion, this expression is identical to that shown above for the minimum Charpy
value for steel frame buildings, namely:
Yst
Cv >

• 710k
  for situations where k = 1.
  In keeping with the situation with the bridge code BS 5400, BS 5950 has not
  yet been updated to reflect the withdrawal of BS 4360 and the introduction of
  European specifications for structural steels. However, amendments to Table 2
  of BS 5950: Part 2 and Table 4 of BS 5950: Part 1 are being prepared to reflect
  the changes in steel nomenclature.

Steels for pipelines

Pipelines are very efficient for the mass transportation of oil and gas and can
extend over vast distances. For example, the Alaskan National Gas Transportation
System involves more than 4000 miles of linepipe in diameters ranging from
42 to 56 in. In Europe, the pipelines from northern Russia to Germany and
Austria extend for more than 3100 miles and are predominantly in 56-in diameter
linepipe. In either case, the operating pressures are up to 1450 lb/in. 2 Over the
past 30 years, the trend in pipeline design has been to larger sizes and higher
operating pressures in order to increase the efficiency of transportation. This has
been accomplished through the provision of steels with progressive increases in
yield strength coupled with good weldability and sufficient toughness to restrict
crack propagation. However, other trends in the extraction of oil and gas have
imposed further requirements on the performance of linepipe steels. These include
the need for high-strength, heavy-waU pipe to prevent buckling during pipeline
installation in deep water, e.g. in depths of 170 m in the North Sea. The operation
of pipelines in arctic regions, coupled with the transportation of liquid natural
gas (LNG), have also imposed further demands for improved levels of toughness
at low operating temperatures. However, a particularly important trend has been
the exploitation of sour oil and gas reserves which has required the development
of linepipe steels with resistance to hydrogen-induced cracking (HIC). Thus in
addition to higher strength and toughness, developing pipeline technologies have
required improved resistance to corrosion which has been met with specific alloy
additions and special control over non-metallic inclusions. Of major importance
in meeting the property requirements of the oil and gas industries have been
the developments in the thermomechanical processing of steel and the bulk of
linepipe steels are now supplied in the controlled-rolled condition.

Specifications and property requirements

Most linepipe specifications in the world are based on those issued by the Amer-

ican Petroleum Institute (API) which cover high test linepipe (5LX series) and