中国微合金化技术与含铌钢发展30周-of Evolution(9)

中国微合金化技术与含铌钢发展30周-of Evolution

High Strength Microalloyed Linepipe: Half a Century of Evolution 29

introduced, which were stimulated both from an alloy design perspective, to aid niobium carbide solubility, and from an end user (specification) initiative to improve field weldability. This led to dramatically improved toughness in the X-60 and X-70 steels shown in Figure 8. These levels of toughness at low temperatures have been preserved/maintained as strengths have almost doubled.

Figure 8: Progress of development showing simultaneous increase in toughness with strength and passage of time.

A representative controlled rolled X-60 steel composition, circa 1980, is presented in Table 4 below. Such steels were used for construction of several major pipelines in Saudi Arabia and the North Sea.

Table 4: Typical X-60 Steel Composition

Steels of API Grade X-70 were successfully used in the construction of the Alyeska oil pipeline in 1973. A typical chemical composition for such steels, which were produced in Japan, is shown in Table 5 below:

Table 5: Example of X-70 Steel Used in Alaska, circa 1972

As mentioned earlier linepipe steels with strengths over X-80 have not been used except in