1. Remove all foreign material such as paint,
THREAD LEAKS
All leaking threaded joints that cannot be tightened
of pipe or tubing for at least 6 inches on each side of the
with a reasonable amount of pull-up should be taken
repair area; it is not necessary to polish the pipe. The
apart, cleaned, and examined to remove bad thread
pipe or tubing should be clean, dry, and free of solvents
conditions. Recoat with a compound suitable for the
and flammable vapors.
intended service, and carefully reassemble to avoid any
2. Pipe or tubing requiring repair may show cracks
other thread damage. Poorly cut threads are a constant
or other defects indicative of incipient failure. In the
source of trouble with threaded joints. Therefore, it is
area to be repaired where such defects are not obvious,
essential that thread cutters receive proper use and care.
liquid-penetrant test the area before pressurizing to
Various thread leak causes and corrective measures
ensure that undetected defects are not present.
to be taken are listed in table 16-6.
For additional information on the characteristics,
special requirements and procedures, and the types and
PREPARATION OF PIPES FOR REPAIR
frequency of tests and inspections to be conducted on
specific piping systems, refer to NSTM, chapter 505. For
more information on the repair of hydraulic systems,
Prepare pipes requiring repair according to the
consult NSTM, chapter 556.
procedures described in the following paragraphs:
Table 16-6.--Thread Leak Causes and Corrective Measures
Correction
Cause of Trouble
Rough Threads:
Sharpen
Dull chasers
Use plenty of good oil
Insufficient lubrication
Grind properly
Excessive or insufficient lead cutting
Grind to correct angle
Grind out entire tooth
Broken tooth in chaser leader
Clean slots, set chasers to true cutting circle, grind
Chaser not set to form true cutting circle
chasers, if necessary, to a uniform length
Shaved Threads:
Regrind lead
Improper lead of chaser
Keep slots clean
Chasers not tracking properly
Correct setting
Chasers not set in correct rotation
Repair carriage
Carriage travel retarded (machine only)
Wavy Threads:
Center die or chasers; get new die head
Die or chasers not true (manual only); loose chasers
(machine)
Tighten with wrench; get new die head
Thumb screws not tight (manual only); worn cam
in head (machine)
Get new die stock
Keep slots clean
Cuttings or dirt in chaser slots (manual only)
Shoulders:
Recut square and rethread
Pipe ends not square (manual only)
Die and chuck not aligned (machine)
Check and realign
16-45