Page 86 - Pipeline Rules of Thumb Handbook

Construction 73

TERMINOLOGY 9–11

Defect parameters closed by rolling or other work but has not been fused into
sound metal.
Defect: A crack, pit, crevice, gouge, dent, metallurgical anomaly, or *Hard spot: An area in the pipe with a hardness level consider-
combination of two or more of the above which is known or sus- ably higher than that of surrounding metal; usually caused by
pected to reduce the effective pipe strength level to less than 100 localized quenching.
percent of its specified minimum yield strength (SMYS). *Crack: A stress-induced separation of the metal which, without
O.D. defect: A defect emanating at and extending radially inward any other influence, is insufficient in extent to cause complete
from the outside surface but not entirely through the wall of the rupture of the material.
pipe.
I.D. defect: A defect emanating at and extending radially outward (b) Defects in the seam weld
from the inside surface but not entirely through the wall of the pipe. *Incomplete fusion: Lack of complete coalescence of some
Interior defect: A defect emanating in the interior of the pipe wall portion of the metal in a weld joint.
but not of sufficient radial extent to be connected with either the *Incomplete penetration: A condition where weld metal does not
inside or the outside surface. continue through the full thickness of the joint.
Leaking O.D. defect: A defect which was initially an O.D. defect, *Under-cut: Under-cutting on submerged-arc-welded pipe is the
but which has grown through the wall to become a leak. reduction in thickness of the pipe wall adjacent to the weld
Leaking I.D. defect: A defect which was initially an I.D. defect, but where it is fused to the surface of the pipe.
which has grown through the wall to become a leak. *Weld area crack: A crack that occurs in the weld deposit, the
Superficial defect: A lap, crevice, pit, group of pits, metallurgical fusion line, or the heat-affected-zone. (Crack: A stress-induced
anomaly, or plain dent (i.e., without scratches, gouges, or cracks) separation of the metal which, without any other influence, is
which is of insufficient extent to reduce the effective strength level sufficient in extent to cause complete rupture of the material.)
of the pipe below 100 percent of SMYS.
*Upturned fiber imperfection: Metal separation, resulting from
imperfections at the edge of the plate or skelp, parallel to the
Kinds of defects
surface, which turn toward the I.D. or O.D. pipe surface when
* (Definitions marked by asterisk are from API Bulletin 5T1 Nonde- the edges are upset during welding.
structive Testing Terminology, Third Edition, April, 1972.) *Penetrator: A localized spot of incomplete fusion.
*Cold weld: A metallurgically inexact term generally indicating a
Not every conceivable kind of defect in pipe is covered by this list. lack of adequate weld bonding strength of the abutting edges,
The list is limited to those which are likely to be encountered in an due to insufficient heat and/or pressure. A cold weld may or
in-service pipeline. may not have separation in the weld line. Other more defini-
tive terms should be used whenever possible.
Defects originating from pipe manufacture
Defects originating from external or internal
(a) Defects not necessarily in the seam weld (primarily in the body environmental degeneration of the pipe
of the pipe)
*Lap: Fold of metal which has been rolled or otherwise worked (a) Seam weld defects
against the surface of rolled metal, but has not fused into Selective corrosion: Preferential corrosion in the fusion line of an
sound metal. electric resistance welded or flash welded longitudinal seam.
*Pit: A depression resulting from the removal of foreign material Hydrogen stress cracking: Environmentally stimulated cracking
rolled into the surface during manufacture. of the weld metal or heat-affected-zone of the longitudinal
*Rolled-in slugs: A foreign metallic body rolled into the metal seam.
surface, usually not fused. (b) Defects not in the body of the pipe (possibly in the seam weld—
*Seam: Crevice in rolled metal which has been more or less but not specifically because of the seam weld)

8. Christian, J. R., and Cassie, B. A., “Analysis of a Live 10. Eiber, R. J., “Field Failure Investigations,” Fifth Sympo-
Welded Repair on An Artificial Defect,” ERS.C.96, sium on Line Pipe Research, American Gas Association,
October, 1975. 1974, Catalog No. L30174.
9. Smith, R. B., and Eiber, R. J., “Field Failure Survey 11. Wright, R. R., “Proper Inspection Methods Minimize
and Investigation,” Fourth Symposium on Line Pipe Pipeline Failures,” Oil and Gas Journal, May 23, 1977,
Research, American Gas Association, 1969, Catalog No. pp. 51–56.
L30075.