Common Problems Encountered In The Use Of Threads

Problem: Mismatching of Standards
Pipe sizes 1⁄2″ and 3⁄4″ have the same pitch and cone taper angle on R and NPT series threads and may appear to screw together without any mismatch. Please remember the two series of threads are completely different in all other respects, and it is recommended that the mixing of the two thread standards does not occur.

Problem: Joining of an R series male thread with G series female thread
The two thread standards are independent of each other, so while the two threads may appear to connect together without any mismatch, problems may occur with:
a) The male thread may screw into the female thread further than designed, thus having a potential to leak.
b) The beginning of the male thread interferes with the end of the female thread. This is a common problem encountered with valves that are screwed with G series threads.
Usually the female thread length is insufficient to accommodate the male thread.

Problem: American standard castings with R series threads
Fittings originally cast to the American Standards ANSI B16.3 and B16.14 that are designed to be machined with an NPT thread, but are subsequently machined with an R series thread. The length of the fitting as cast is found to be too short, to produce an R series thread to its correct length.

Problem: R series threads locking up in the wash out part of the thread
This is easy to check, male thread should have two to three threads exposed after hand tight engagement with a female thread, this is to allow the joint to be wrench tightened.

Problem: Rp thread machined or tapped oversize
The male thread engages too deeply and lock up could occur in the wash out of the thread, or the front face of the male fitting could foul with the end of the female thread.

Problem: Insufficient thread engagement
NPT male and female threads manufactured to maximum and minimum tolerance respectively, the amount of engagement could be limited to as little as one turn. Fitting blow-out may occur with the introduction of high pressure.

Problem: Incorrect thread form
NPT threads machined with the incorrect thread form, thus the possibility of leakage or thread blow out.


The Solution

Prochem Pipeline Products is Australia’s leading manufacturer of stainless steel threaded fittings, with all fittings manufactured in complete accordance with the various International fitting standards, under the strict control of a Quality Assurance System certified to ISO 9001 by Lloyd’s.
All of the problems as detailed within, have been identified, and indeed rectified, by Prochem, with industry Australia wide gaining the benefits of our local expertise.
If you have concerns about fitting problems you may be experiencing or in fact you require a particular fitting product to meet your special application, then please do not hesitate to contact your nearest Prochem office.
At Prochem, we have the quality of product and service, the experience and the expertise, to provide the solutions to your fitting problems, and we are only too pleased to assist in any way we can:
that’s the Prochem advantage.

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