During the last decade, the specifications, WES-135 and -136 played important guiding roles for developing and standardizing weldable high strength steels and structural steels for low temperature applications. In WES-135 which was established in September 1970, equivalent carbon content,
C
eq
is adopted as an indication of the weld cracking susceptibility for high strength steels In order to accurately estimate the cracking susceptibility, a new parameter,
P
cm
, is adopted as an indication of the carbon equivalent since March 1971. On the other hand, the toughness requirements specified in WES-136 are based on the correlation between small-scale tests and large-scale brittle crack propagation arrest tests as expressed in terms of
K
c
-value. In this standard, steel plates are classi e into two classes of G and A, where G is generally accepted for welded structures where hazard of brittle fracture is anticipated and A is used for arresting a propagating crack. In order to establish revised toughness requirements for G class steels, comprehensive cooperative research works have been conducted since 1971. In this paper, the descriptions are focused on the weldability and toughness requirements of WES-135 and -136, their connexions with other standards, and the points under continuous examination.
