Thread seal tape is a polytetrafluoroethylene film for use in sealing pipe threads. The
tape is sold cut to specific widths and wound on a spool, making it easy to wind around
pipe threads. It is also popularly but incorrectly called Teflon tape in spite of DuPont, the
holder of that trademark, no longer manufacturing it. Thread seal tape lubricates allowing for
a deeper seating of the threads, and it helps prevent the threads from seizing when being
unscrewed. The tape also works as a deformable filler, helping to seal the joint without
hardening or making it more difficult to tighten, and instead making it easier to tighten.
Typically the tape is wrapped around a pipe's thread three times before it is screwed into
place. It is commonly used commercially in applications including pressurized water systems,
central heating systems, and air compression equipment.
Types
There are two US standards for determining the quality of any PTFE tape. MIL-T-27730A
requires a minimum thickness of 3.5 mils and a minimum PTFE purity of 99%. The second standard,
A-A-58092, is a commercial grade which maintains the thickness requirement of MIL-T-27730A
and adds a minimum density of 1.2 g/cm3. Relevant standards may vary between industries;
tape for gas fittings is required to be thicker than that for water. Although PTFE itself
is suitable for use with high-pressure oxygen, the grade of tape must also be known to be
free from grease. Thread seal tape used in plumbing applications
is most commonly white, but it is also available in various colors. White PTFE is single density,
yellow is double and pink is triple . It is often used to correspond to color coded pipelines.
These color-codes for thread sealing tape were introduced by Bill Bentley of Unasco
Pty Ltd in the 1970s. In the UK, tape is used from coloured reels, e.g. yellow reels for
gas, green for potable water. White – used on NPT threads up to 3/8 inch
Yellow – used on NPT threads 1/2 inch to 2 inch, often labeled "gas tape"
Pink – used on NPT threads 1/2 inch to 2 inch
Green – oil-free PTFE used on oxygen lines and some specific medical gasses
Gray – contains nickel, anti-seizing, anti-gailling and anti-corrosion, used for stainless pipes
Copper – contains copper granules and is certified as a thread lubricant but not a
sealer In Europe the BSI standard BS-7786:2006 specifies
various grades and quality standards of PTFE thread sealing tape.
Uses PTFE tape can be used for propane on spud
guns, for small diameter pipe like 1/4 inch meter equipment. Yellow tape is for gas because
it is stronger and will not clog a gas valve.
Thread tape is appropriate for use on tapered threads, where the sealing force is a wedge
action. Parallel threads may not seal effectively with or without tape, as they are intended
to be sealed by a gasket. Thread sealing tape is almost entirely applied
by hand, although at least one machine is available for production wrapping of fittings.
PTFE tape is also commonly used in the stretching of body piercings, through a process known
as taping, because it is inert and safe for this use. The wearer wraps layers of the tape
around a plug, slowly increasing the size and thus slowly increasing the size of the
piercing. Hazards
Overuse or misapplication of thread tape may be a hazard. Excess application of PTFE tape
can prevent mating threads from fully engaging, reducing the shear point of the threads. Combining
thread-seal tape with a pipe dope compound can also overload threads. Also, internal
overhangs of loose material may constrict a joint or slough off and form a foreign body
that could jam a valve seat. Therefore, use of PTFE tape as a thread sealant is generally
not considered appropriate in fluid power systems.
Misnomer Familiarity with the Teflon brand of fluoropolymers
has led to the practice of errently referring to PTFE-based thread seal tape as "Teflon
tape". DuPont, owners of the Teflon trademark, no longer manufactures any thread seal tape,
and the company has launched a campaign against the practice.
See also Pipe dope
References