Quality
Waterjet Newsletter – 06/13/2006
Pressure Limits of Tapered Pipe Thread Connections An experimental study was conducted
by Wright et al* to determine the maximum allowable pressures for tapered
pipe thread connections used in the waterblast
industry. Its main points are reviewed here. The two popular equations for
calculating burst pressure of a cylinder are as follows: Barlow equation for thin walled
cylinders (ID/wall > 10)
Lame’ equation for thick walled
cylinders (ID/wall < 10)
Where P = burst pressure, S =
tensile strength of material, t = wall thickness, D = outer diameter, w =
wall ratio (OD/ID). All the test
samples in this study had a wall ratio less than 10. Using a safety factor of
2.5, specified by Waterjet Technology Association, the maximum allowable
operating pressure can be calculated with P/2.5. Tests were done to verify these two
equations applied to tapered pipe thread connections. Test samples (including
6 solid plugs, 24 male pipes, 16 pipe couplings) were made from 303, 304A
bar, 304L seamless schedule 160 pipe and 17-4 H900
stainless steel. Tests with different thread engagement and multiple
assemblies were also done. A single stroke intensifier pump (80 kpsi maximum operating pressure) was used for most of the
tests. In some cases leakage of test fitting exceeded the capacity of the
intensifier pump and then a triplex plunger pump (40 kpsi
maximum) was used instead.
Reported test results include
failure pressure and failure mode of each test, photos of tested samples
showing the failure modes, as well as comparison with calculated values. To
the left is a graph that illustrated the ratio of calculated values to actual
failure pressures. It appears that Lame’ equation most accurately predicts
the failure pressure. *Wright, D., Wolgamott, J., and
Zink, G. (2003) Pipe threads --- what is the limit? Proceedings of the 2003
WJTA American Waterjet Conference, Beyong High Pressure ·
Courtesy to Prof. O.V. Krishnaiah
Chetty, an electronic copy of his paper “Studies
on Recharging of Abrasives in Abrasive Water Jet Machining” is now available
at http://www.qualjet.com/Newsletter/RechargingAbrabsive.pdf.
Professor Chetty can be reach at ovk@iitm.ac.in. |
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