Why Class 9000 threaded forged fittings are not published and connections are not guaranteed to hold

[snoffs]

A 3/4" Class 6000 threaded forged fitting is shown to have an equivalent wall thickness of a 3/4" XXS CS pipe per ASME B16.11. If you were to calculate the MAWP using SA-106 material, an 1/8" CA, both a taper allowance and a thread allowance, you would end up with a MAWP close to 4500 psig at ambient temperature.
A 1500# CS flange is rated for around 3700 psig at ambient. The 1500# piping class require class 9000 fittings, and CL 9000 threaded fittings are not published in the ASME B16.11 standard. I contacted MRC Global and asked why manufacturers like Bonney Forge do not publish the CL 9000 threaded fittings, and the response i received was that the manufacturer does not guarantee the threads at that high of pressure. What I don't understand is why they don't guarantee the threads if the connections are rated for more than enough pressure. Is it because there's no confirmed "hand tightening" method of the joint that will be enough to withstand the pressure?

Does anyone know why the CL 9000 threaded fittings aren't published in any standard, why the CL 9000 rated fittings are required for the CL 1500# flange piping system, and why the manufacturers wont guarantee the threads will hold at the pressure rating? Thanks in advance for your replies.

 

[hacksaw]

using pipe threads above in process chemical plants is asking for trouble.

in processes that ar not leak critical then your heavier guage fittings are for mechanical stiffness and corrosion allowance,

my two cents,

 

[MJCronin]

At Higher pressures, socket welded fittings are the wise choice.

Be sure that the weld is large enough in accordance with ASME B31.1 and B16.11

MJCronin
Sr. Process Engineer