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 TB 55-1900-232-10
the chain be cut out and a detachable link inserted. If the major portion of the chain has loose studs, the chain
should be scrapped.
Any grinding to eliminate shallow surface defects should be done parallel to the longitudinal direction of the
chain, and the groove should be well rounded and should form a smooth transition to the surface. The ground
surface should be examined by magnetic- particle or dye-penetrant inspection techniques
D-9 TYPES OF WEAR
The rough treatment to which chain items of towing gear are exposed can lead to various chain problems. Eight
such common problems for which towing personnel should be alert are described below.
a. Missing studs. the stud contributes about 15 percent of the chain's strength A chain link without a stud
may significantly increase the possibility of link failure. High bending stresses and low fatigue life in links
are predictable consequences of missing studs
b. Bent links: a bent link is the result of chain handling abuse. The link may have beenexcessively torqued
when traversing a sharp, curved surface or the chain may have jumped over the wildcat, making point
contacts between the link and the wildcat
c.
Corrosion: excessive corrosion increases the possibility of chain failure from corrosion fatigue or
overloading due to reduced cross-sectional area.
d.
Sharp gouges: physical damage to the chain surface, such as cuts and gouges, raises stress and
promotes fatigue failure.
e. Loose studs: loose studs, caused by abusive handling or by excessive stretching of chain, result- ing in
lower bending strength of the chain.
f. Cracks: surface cracks, flash weld cracks and stud weld cracks propagate under cyclic loading, and result
in premature chain failure.
g. Wear. wear between links in the grip area and between links and the wildcat reduces the chain diameter
The diameter reduction decreases the load-carrying capacity of the chain and invites failure.
h.
Elongation: excessive permanent elongation may cause the chain to function improperly in the wildcat,
resulting in bending and wear of the links. Wear in the grip area of the chain as well as working loads m
excess of the original proof load will result in a permanent elongation of chain.
D-10 SPECIAL PRECAUTIONS
Chain generally is the most rugged component of the towline system Because of this, there may be a tendency
to become overconfident in its capability and somewhat lax m inspection. Avoid overconfidence when using
chain.
Personnel tend not to check carefully enough on such items as:
a
Adequate radius of curvature on surfaces of fair- leads, chocks, etc. A ratio of 7:1 is generally accepted
as the minimum D:d ratio of bearing surface to chain size for heavy loads when the chain direction is
changed significantly over the surface
b. Wear in the grip (partially-hidden contact) area between chain links.
c.
Looseness from excessive wear in shackles, swivels and detachable links.
d. Presence of detachable links that are not equipped with safety-lock hairpins.
e. Screw-pin shackles, which should never be used in towline connections
D-4
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