SINGLE-PHASE ALTERNATING CURRENT: This term refers to a simple current, alternating in direction.
Commercial single-phase current follows a sine wave. Such a current requires only two conductors for its circuit. Most
common commercial frequencies are 25,50 and 60 cycles per second.
SKIN EFFECT (MT, EC): The phenomenon that causes current to flow along the surface of a conductor. As frequency
increase, skin depth decreases.
SKIP DISTANCE (UT): In angle beam testing, the distance from the sound entry point to the first reflection point on
the same test surface; also sometimes called V-Path.
SKY SHINE (RT): Scatter radiation caused by interaction of the X-ray photons with the atoms in the air molecules, or
structures in the vicinity, and radiates back toward the earth. Skyshine can be detected at considerable distance from
the source, therefore, it should be considered when establishing barriers, etc.
SLAG: A non-metallic residue that forms on molten metal as a result of the combining of impurities.
SLAG INCLUSIONS: Nonmetallic solid material entrapped in weld metal or between weld metal and base metal.
SLAG LINES: Elongated cavities containing slag or other foreign matter.
SLIP LINES: (Slip Bands) Traces of slip planes observed at low magnifications on the polished surface of a crystal
which has been deformed after polishing.
SLIP PLANES: In a given metal, slip occurs most easily along certain croplatographic planes. Hence, these planes are
termed slip planes.
SLOUGHING (RT): The loosening of an emulsion from its base, commencing at the edges. It is usually caused by
prolonged immersion in a liquid at too high a temperature or of unsuitable chemical composition.
SLUGGING (STUBBING): The addition of a separate piece or pieces of material in a joint before or during welding.
S-N DIAGRAM: A plot showing the relationship of stress, S, and the number of cycles, N, before failure in fatigue
SNELLS LAW (UT): Law that defines the angle of incidence and angle of refraction or mode conversion; expressed
sinØl divided by sinØ2 =
V1 divided by V2
Ø1 = angle (measured from the normal to the interface surface) of the incident sound beam.
Ø2 = angle (measured from the normal to the interface surface) of the refracted or mode converted beam.
V1 = velocity of incident sound beam.
V2 = velocity of refracted or mode converted sound beam.
SOAKING: Prolonged holding at a selected temperature.
SOAK TIME (PT): The period of time wherein parts are immersed in a bath of liquid penetrant.