Page 56 - Oil&Gas-AustralAsia-2015-Issue-2
P. 56
S UBSEA
High-specification, tight tolerance threads ensure
reliable service for high-pressure pipe valves
The oil and gas industry’s continu- too much room for error, and a risk of .71875
ing push into more severe operating thread failure.
environments, from deeper HP/HT BuTech addresses these concerns in the ANPT
reservoirs to deepwater subsea process- ANPT spec with its own specification
ing systems located miles away from that tightens the tolerance such that .688
producing platforms, is placing greater the threads can be confidently used at
demands on equipment to operate higher pressures. The BuTech specifica- BuTech
safely and reliably at high pressures. tion was set after a thorough research
Hydraulic and pneumatic piping and program designed to identify the ideal Figure 1: Drill Tap Sizes for ½” ANPT versus
subsea chemical injection modules, for taper gage in the male/female set of the BuTech
example, must operate at pressures of fitting that would provide the maxi-
up to 10,000 psi or more. If a high-pres- mum surface contact area. cation had a minimum pitch diameter,
sure failure is to occur, it will most For the female part of the fitting, a but not a basic or maximum. This was
likely happen at one or more fittings in 6-step minor gage is used to verify the determined on the 6-step ANPT ring
a valve assembly. proper taper of the male and female gage that showed how large the outer
Lowering the risk of fitting failure components and indicates any trun- pitch diameter and major diameters
is a major priority for suppliers of cation. Upon full engagement, the were. Based on this information, the
severe-service pipe valves and fit- ideal thread opening on the female end most optimal setup for the male with
tings, and much focus has centered on should ensure that the minor gage is the Butech ANPT female would be for
developing high-quality, tight-tolerance fully secure without a shaky fit (indi- the male to fall within the minimum to
threads. The Aeronautical National cating no excessive truncation), correct basic scope. These parameters allowed
Pipe Thread (ANPT) was developed for minor diameter, and correct taper as the male to fit in properly with the fe-
high-pressure service and uses strict per the BuTech spec. male ANPT part without the risk of any
machining standards and practices to Some of the tap drills could be on the potential leakage or thread blowout.
machine threads that are sharp, precise minor end, meaning that the tap drill With this research as a guide, BuTech
and provide the proper truncation. size was too small. As a result, the mat- developed its machining process to en-
ANPT threads are also held to high in- ing (male) part would engage no more sure that both the female and male ends
spection practices, using gages to meas- than two turns into the female end, of each fitting fell within the required
ure the L1, L2 and L3 depths as well as raising the risk of a blowout with the specification. This created a carefully
the minor diameter. The machining mating part being so close to the opera- controlled taper on the threads that
process also minimizes imperfect tional edge. Some of the tap drills were maximized the surface contact area.
threads, thus ensuring proper sealing on the maximum side, meaning that the Further laboratory testing was con-
between the male and female ends and male gage would engage deeper but that ducted to compare the controlled taper
a higher pressure specification of 10,000 the minor diameter of the female thread of the BuTech thread with a standard
psi. Filler material such as Teflon tape would not properly encompass the male ANPT thread. A total of 32 test samples
is not required for the ANPT thread, part, thus resulting in a less secure fit. were prepared, with variables including
reducing the risk of contamination The basic side (a tight range between the tap drill size, the L1 engagement,
between the threads. the minor and major ends) showed the and the L3 engagement. These samples
greatest potential. Based on further conclusively showed that the BuTech
The BuTech spec investigation and design, the basic ANPT thread fitting could reliably and
tolerance provided the most secure fit consistently produce a high-integrity
While the ANPT thread provides and optimal amount of engagement. In
improved reliability in high-pressure addition, the sharp threads are main-
applications, its tolerance band (a tained and controlled using a specific
measure of the amount of variation thread insert designed for ANPT
permitted from the thread’s designated purposes. Maintaining the sharp thread
dimension) is still too wide for some provides a more sufficient seal between
oilfield applications where pressures the mating parts.
exceed 10,000 psi. In fact, the specifi- A similar investigation of the male end
cation for the standard ANPT thread showed that the standard ANPT specifi
indicates that the mating part engages
at anywhere from 2.5 to 4.5 turns, but
is only rated to 8,000 psi. This leaves
A A54 OIL & GAS ustral SIA MAY/JUNE 2015 www.oilandgasaustralasia.com
High-specification, tight tolerance threads ensure
reliable service for high-pressure pipe valves
The oil and gas industry’s continu- too much room for error, and a risk of .71875
ing push into more severe operating thread failure.
environments, from deeper HP/HT BuTech addresses these concerns in the ANPT
reservoirs to deepwater subsea process- ANPT spec with its own specification
ing systems located miles away from that tightens the tolerance such that .688
producing platforms, is placing greater the threads can be confidently used at
demands on equipment to operate higher pressures. The BuTech specifica- BuTech
safely and reliably at high pressures. tion was set after a thorough research
Hydraulic and pneumatic piping and program designed to identify the ideal Figure 1: Drill Tap Sizes for ½” ANPT versus
subsea chemical injection modules, for taper gage in the male/female set of the BuTech
example, must operate at pressures of fitting that would provide the maxi-
up to 10,000 psi or more. If a high-pres- mum surface contact area. cation had a minimum pitch diameter,
sure failure is to occur, it will most For the female part of the fitting, a but not a basic or maximum. This was
likely happen at one or more fittings in 6-step minor gage is used to verify the determined on the 6-step ANPT ring
a valve assembly. proper taper of the male and female gage that showed how large the outer
Lowering the risk of fitting failure components and indicates any trun- pitch diameter and major diameters
is a major priority for suppliers of cation. Upon full engagement, the were. Based on this information, the
severe-service pipe valves and fit- ideal thread opening on the female end most optimal setup for the male with
tings, and much focus has centered on should ensure that the minor gage is the Butech ANPT female would be for
developing high-quality, tight-tolerance fully secure without a shaky fit (indi- the male to fall within the minimum to
threads. The Aeronautical National cating no excessive truncation), correct basic scope. These parameters allowed
Pipe Thread (ANPT) was developed for minor diameter, and correct taper as the male to fit in properly with the fe-
high-pressure service and uses strict per the BuTech spec. male ANPT part without the risk of any
machining standards and practices to Some of the tap drills could be on the potential leakage or thread blowout.
machine threads that are sharp, precise minor end, meaning that the tap drill With this research as a guide, BuTech
and provide the proper truncation. size was too small. As a result, the mat- developed its machining process to en-
ANPT threads are also held to high in- ing (male) part would engage no more sure that both the female and male ends
spection practices, using gages to meas- than two turns into the female end, of each fitting fell within the required
ure the L1, L2 and L3 depths as well as raising the risk of a blowout with the specification. This created a carefully
the minor diameter. The machining mating part being so close to the opera- controlled taper on the threads that
process also minimizes imperfect tional edge. Some of the tap drills were maximized the surface contact area.
threads, thus ensuring proper sealing on the maximum side, meaning that the Further laboratory testing was con-
between the male and female ends and male gage would engage deeper but that ducted to compare the controlled taper
a higher pressure specification of 10,000 the minor diameter of the female thread of the BuTech thread with a standard
psi. Filler material such as Teflon tape would not properly encompass the male ANPT thread. A total of 32 test samples
is not required for the ANPT thread, part, thus resulting in a less secure fit. were prepared, with variables including
reducing the risk of contamination The basic side (a tight range between the tap drill size, the L1 engagement,
between the threads. the minor and major ends) showed the and the L3 engagement. These samples
greatest potential. Based on further conclusively showed that the BuTech
The BuTech spec investigation and design, the basic ANPT thread fitting could reliably and
tolerance provided the most secure fit consistently produce a high-integrity
While the ANPT thread provides and optimal amount of engagement. In
improved reliability in high-pressure addition, the sharp threads are main-
applications, its tolerance band (a tained and controlled using a specific
measure of the amount of variation thread insert designed for ANPT
permitted from the thread’s designated purposes. Maintaining the sharp thread
dimension) is still too wide for some provides a more sufficient seal between
oilfield applications where pressures the mating parts.
exceed 10,000 psi. In fact, the specifi- A similar investigation of the male end
cation for the standard ANPT thread showed that the standard ANPT specifi
indicates that the mating part engages
at anywhere from 2.5 to 4.5 turns, but
is only rated to 8,000 psi. This leaves
A A54 OIL & GAS ustral SIA MAY/JUNE 2015 www.oilandgasaustralasia.com
