> The effects of welding on bolts, both high and low carbon
> contents. Any comments or advice will be appreciated.
It's safe to say it depends upon the bolts, when you do it, and the
Structural bolts such as A325s and A490s are heat-treated to attain their
strength/mechanical properties during manufacture. (Quenched and tempered at
800 deg F min.) Welding on such bolts will affect those properties, lower
their strength, and impede or negate tightening efforts. (Or relax those
which have already been fully tightened.)
All four RCSC bolt tightening methods would be affected by welding on a bolt
before tightening, each differently. For example, if one were using the
'turn-of-nut' tightening method, the specified turn will no longer lead to
attainment of the required minimum tension. Even if 'match-marks' were
used, they would no longer be indicative of a fully-tensioned bolt when
inspected by the party contracted for that task.
Similarly, welding on a twist-off bolt (ASTM F1852) before shearing of the
break-neck will alter its properties and destroy the proprietary lubricant
which has been applied to the fasteners in an attempt to control the
torque/tension relationship. The heat associated with welding even in
proximity to such lubricants typically raises the 'k' (aka 'nut' or
'friction' factor) and will result in shearing of the break-neck element
before attaining minimum required tension. Many such lubricants are
water-based, so it doesn't take much heat. Thus, inspection to verify
shearing of the break-necks will not correlate with tension. Likewise, the
'Calibrated Wrench' method will suffer the same fate, as the lubricant will
suffer ---- even before the fastener's mechanical properties are altered.
Further inspection by torque wrench will not 'catch' this fact.
Lastly, the Direct Tension Indicator (ASTM F959) method could be affected
too. Just like all other heat-treated fasteners, the mechanical properties
of Load Indicating Washers will show signs of being altered as temperatures
approach within ~150 deg. F of the tempering temperature used in their
manufacture. Thus, a flattened DTI would not necessarily mean a properly
tightened bolt. If only the bolts were welded upon and the DTI unaffected,
the likely result would be bolt breakage in a vain attempt to flatten the
load indicators. (A phonecalls from irate ironworkers to my office telling
me our load-indicators are too strong.)
In general, welding on any heat-treated fastener is a risky proposition at
best. We 'fastener people' react poorly when anyone alters the mechanical
properties of our parts. Yet, in shear connections a 'soft' part probably
won't be any worse ----- except that softening of a fastener with a welding
torch brings factors that we don't usually have to consider. We have the
benefit of softening (tempering) in controlled atmospheres. I would imagine
welding on a part is much more likely to introduce cracks and
discontinuities --- things that could affect shear values and other
If I haven't gone on too far already, consider this: The Fastener Quality
Act of 1990 considers any person who 'alters the mechanical properties of a
fastener' as the new manufacturer, and thereafter requires that party to
fully test the fasteners in a NIST-accredited laboratory, mark them with his
or her own 'manufacturer's ID marks' and provides for fines of
$25K/violation for those who choose not to.
So --- borrowing from Jay Leno's chip commercial, "Go ahead and weld on
them, as long as you throw them away rather than leave them in any part of
the structure . . . . We'll make more."
David F Sharp
57 E. 11th St.
New York, NY 10003