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Installing and Removing
Tap End Studs in
The bolts installed in tapped holes in API studded face flanges should always have
double end, or tap end stud,
configuration. The studs should have a short thread on one end with only
enough threads to assure a thread engagement with the tapped hole equal
to one diameter of the stud. This short thread should have an end of
thread run-out on the stud body of 45° to 60° to facilitate a jam
between the end of the thread and the top of the tapped hole.
Note: When installing tap end
studs into tapped holes, always apply generous lubrication to the tap end
thread of the stud, do not apply much, or any, lubricant in the tapped
hole. Lubricant trapped below the stud in the tapped hole
may prevent full thread engagement. 1
Jamming the hole with the stud, in the manner described, will
cause visible distortion to the first thread at the top of the hole.
This jamming will tend to form a seal at the top of the tapped hole,
between the stud and the equipment body, preventing the escape of
lubricant used in the hole and on the stud, helping to prevent the
entrance of water. This jamming, at the top of the hole, will provide a
gripping phenomenon to retain the stud in the hole when removing nuts
during field use.
overdo it when jamming the stud in the tapped hole, moderate jamming
will work OK. Do not attempt to use all thread studs in tapped holes,
and do not engage the long thread end of tap end studs into the tapped
holes. Jamming the stud threaded ends into the bottom of the holes will
cause galling at the bottom of the holes, and removal of the stud, if
possible, will also remove the threads from the tapped hole. Avoid
products like Loc-Tite. 1
Tap end studs properly installed, jammed enough to
avoid un-intended back-out from the tapped hole, may prove somewhat difficult to
remove from the tapped holes. The act of jamming the stud at the time of
installation will cause distortion in the top thread of the tapped hole,
this distortion will vary with the extent of jamming force used to secure
the stud. Severe jamming may cause first thread galling in the tapped hole.
If galling has occurred in the first thread of the hole, the galled portion
of the tapped hole may seriously damage the threads on the stud during
removal, making reuse of the stud difficult or impossible. In most cases
removal of tap end studs previously jammed in tapped holes will require
careful re-tapping of the holes by hand so as to accept replacement studs.
Operators may use special equipment to remove tap end studs to
avoid damage to reusable studs. Studs damaged or corroded making them
unsuitable for reuse may be removed with a simple pipe wrench, or when
the nuts also appear unusable the operator may choose to weld them to
the end of the stud (using pre-heat of the stud and nut before welding) and remove the stud with a power wrench fitted to
the welded nut.
Note: At WOODCO USA, in cases where equipment must have special
coatings applied after final hydrotest, we install tap end studs by hand
without tightening or jamming in any way, so that removal after test
will not damage the equipment or the tap end studs.
Words in bold italic indicate they have subjective meaning and persons using this information must use experience to improve the reliability of their judgement when the meaning of these words can have impact on performance.
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that includes Tap End Studs and other API Connector Accessories.
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