A discontinuity found on the fracture surface of a weld in steel that consists of a small pore or inclusion surrounded by an approximately round, bright area.
Fisheyes in welded metal appear as circular and slightly conical spots, 0.4 to 3.2 mm (1/64 to 1/8 in.) diameter, exhibiting a brittle white fracture of two or more concentric rings in contrast with the gray ductile matrix. Fisheyes often contain one or more radial cracks emanating from a central nucleus (an inclusion, a shrinkage or a gas micro-void) and ending in one of the concentric rings. There are several possible causesfor the formation of fisheyes:
(1) Microscopic particles of mechanically entrapped slag, regardless of the structural constitution of the deposit, and, depending on interpass temperature, a heterogeneous condition of microstructure possessing differential ductility.
(2) Incipient micro-cracks developed by the drastic quenching undergone by filler metal when deposited on un-preheated base material.
(3)The. fact that the high-pressure hydrogen gas contained in small discontinuities exerts an aerostatic stress on the metal surrounding the discontinuity, but is not large enough to rupture without external aid.
It takes an externally applied stress to actually initiate fissuring in steel under stress from hydrogen. When the sum of the aerostatic and applied stress exceeds the strength of the steel, the metal ruptures internally to the extent indicated by the surrounding circular area; the pressure of the gas is reduced, tearing abates and a flake remains in a plane perpendicular to the direction of that stress. The concentric rings are probably associated with the degree of hydrogen embrittlement around the defect. It is believed that the central nucleus, the circular form, and the brittle break identify a hydrogen defect.
5F
A welding test position designation for a circumferential fillet weld applied to a joint in pipe, with its axis approximately horizontal, in which the weld is made in the horizontal, vertical, and overhead welding positions. The pipe remains fixed until the welding of the joint is complete.
5G
A welding test position designation for a circumferential groove weld applied to a joint in a pipe with its axis horizontal, in which the weld is made in the pat, vertical, and overhead welding positions. The pipe remains fixed until the welding of the joint is complete.