CEMP-E
TI 809-26
1 March 2000
direct-welded flange joints in beam-to-column moment connections, and at the ends of built-up member
welds such as girder web-to-flange welds. Weld tabs allow the welding of the full width of the joint,
without starts and stops or build-out regions along the edges. The use of weld tabs places the inherent
weld discontinuities made when starting or stopping a weld within the tab, and outside the major stress
flow of the spliced material. Tabs also allow the welding arc to stabilize prior to welding the main
material. For SAW, the tabs support the flux deposit at the edge of the workpiece.
(1) After welding is completed, the weld tabs may need to be removed. In some joints, particularly
in fatigue and high-seismic applications, it may be recommended or necessary to remove the weld tab
after use. Removal is required in most fatigue applications. In heavy section tensile splices, removal is
required. In high seismic regions, removal is required at transverse groove welds in moment-resisting
joints. For other applications, removal should be considered when splicing members over 25 mm (1 in.)
in thickness when the members are subjected to high tensile stresses at the splice. This is because
thicker members typically have less toughness than thinner members, and the low toughness may allow
a crack or other discontinuity in the weld tab to propagate into the primary weld. For compression joints
such as column splices, or for low-stress tensile splices, weld tabs in statically loaded structures should
be allowed to remain in place.
(2) AWS D1.1 Section 5.31, provides information on the use and removal requirements for weld
tabs.
k. Welding Sequence and Distortion Control. Parts can be preset in a skewed position so that, when
weld shrinkage occurs, the completed member will be approximately straight. WPSs that use large
passes, rather than numerous small passes, generally cause less angular distortion. Distortion may also
occur along the length of a member, resulting in unintended sweep, camber, or twist. This occurs
because welding is not balanced about the center of gravity of the member cross-section. The use of
intermittent welding, welding from the center of the member's length, and overwelding in some locations
may also be used to reduce longitudinal distortion.
l. Lamellar Tearing. Lamellar tearing is a step-like crack in the base metal, generally parallel to the
rolled surface, caused by weld shrinkage stresses applied to the steel in the through-thickness direction.
The steel is somewhat weakened by the presence of very small, dispersed, planar-shaped, nonmetallic
inclusions, generally sulfur-based, oriented parallel to the steel surface. These inclusions serve as
initiation points for tearing. Large inclusions constitute laminations, which may be detectable using
straight-beam ultrasonic testing prior to welding. The inclusions that initiate lamellar tearing are generally
not reliably detected using any form of NDT.
(1) There is no specific through-thickness at which lamellar tearing will or will not occur, nor
specific values for weld size, stresses or strains that will induce tearing. Generally, lamellar tearing is
avoided by using one or more of the following techniques: improved design or redesign of the joint,
welding procedure controls, weld bead placement selection, sequencing, the use of preheat and/or
postheat, the use of low-strength, high-ductility filler metals, "buttering," and peening. AWS D1.1
Commentary C2.1.3, provides guidance on these methods. Steels with improved through-thickness
properties may also be specified. The most common method for improving through-thickness properties,
to reduce the risk of lamellar tearing, is the specification of low-sulfur or controlled sulfur-inclusion steels.
(2) Should lamellar tears be detected, the stress type, application, and the implications of potential
failure in service should be considered. Because the completed joint is more highly restrained than the
original joint, repair of joints that have torn is difficult and expensive, with no assurance that a tear will
not form beneath the repair weld. Repair may involve complete removal of the existing weld and
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