中国微合金化技术与含铌钢发展30周-of Evolution(10)

中国微合金化技术与含铌钢发展30周-of Evolution

30 中国含铌钢技术发展30周年国际研讨会论文集

small (5 km) demonstration projects. The workhorse grades for onshore pipelines are currently API Grade X-70 (482 MPa) and API Grade X-80 (550 MPa) with the latter taking on increasing importance.

The chemical compositions in current use are presented in Table 6 below. Niobium and vanadium may be used in combination with molybdenum, chromium, copper and nickel depending on pipe wall thickness, alloy costs and available manufacturing equipment. Each pipe mill thus arrives at an optimized steel composition and production cost matched to it’s engineering capability.

* S<0.005 N<0.008 Al 0.02-0.05

Table 6: Examples of X-80 Steels in Current Use.

The Nb-Cr alloy design has emerged in the past few years as a favorite of Chinese [34-44] and other pipe producers. The 0.10 percent niobium (HTP) steel has a much wider processing window than conventional Nb-V type steels, Figures 9-11 [45] which results in less variation in toughness and yield strength, the later being an important consideration in the current regulatory climate in the United States.

Figure 9: Wide Processing Window for Yield Strength of 22 mm Plates ACC at 6ºC/s [45].