Max pressure for standard 3/4 plumbing pipe

Do you know the maximum (air or oil) pressure
that 3/4" plumbing pipe or black (non galvanized) can handle.

Many thanks !

Joe Ferguson

Tricky Question, the answer is that it depends.

Based upon my Mark's Standard Handbook for Mechanical Engineers ....

For 3/4" steel pipe with a working stress of 12,000 psi (i.e., max working stress for ASTM A120 pipe)

Schedule 40, 0.113" wt, 2,582 psi
Schedule 80, 0.154" wt, 3,520 psi
Schedule 160, 0.218" wt, 4,982 psi

Schedule Numbers are per ANSI B36.10.

The main concern will be with the fittings that you use with the pipe.

Most fittings available from hardware stores and building supply stores are for nonshock service (i.e., hot and cold water plumbing) at temperatures below 300F. They are at best capable of withstanding a pressure of 150 psi.

For use with an airline system, I would recommend purchasing what are known as 300lb fittings. These are rated for use at 300 psi with saturated steam. They can withstand a higher pressure in cold use (i.e., less than 300F). Also available are 150lb fittings. They are available from plumbing supply dealers.

For a hydraulic system, you will need to know what the relief valve setting is on the system. Steel fittings are available with pressure ratings up to 6000 psi.
You can order these fittings by referring to the pressure rating; i.e., 1500lb, 3000lb, 6000lb, etc.

Hope this helps.

It is true that the pressure may be way up from the pump capacity or releif valve setting.

Example: if you grade backward with the loader
bucket tilted...or if bucket is loaded "big hay bale" and tractor moves on a rough surface.

This may be avoided by using spool valves with
integrated releif valve which has to be adjusted according to your particular hydraulic system specifications.

Thanks again !

Joe Ferguson

I assume you are talking about carbon steel pipe and not copper tubing or PVC "plumbing pipe". For carbon steel without quality assurance documentation (like the pipe you would get in a hardware store or home center) in the standard weight (schedule 40) wall thickness and 3/4" nominal size, the maximum safe working pressure is about 2000 psig for temperatures up to a maximum of about 400 deg F. Note that this is for new carbon steel PIPE ONLY (not tubing). Do not use PVC for compressed air use at any pressure. It is not recommended and is potentially unsafe for that application.

Rod

If you have something specific, please advise. I certainly do not want to provide incorrect or unsafe information here. My data comes based on the American National Standard Code for Pressure Piping, ANSI/ASME B31.1, Power Piping. It probably doesn't specifically apply to mobile hydraulic systems. There may be an SAE standard that does, although I would not expect there to be large differences.

Rod

I am talking about steel pipe that we have to
make treads at each end "pipe tread" this type
of pipe was used for plumbing in houses many years
ago. 2000 PSI will be ok for compressed air lines
at 110 PSI...I will check the pressure from the
hydraulic pump of the MF-135 to be sure I can use
this type of pipe safely.

Thanks again

Joe Ferguson

The others are correct about the threaded fittings. You should not use cast, at least not for the hydraulic system. My recommendation would be forged steel only. You are not likely to find these in home centers. Weatherhead makes forged steel threaded pipe fittings for hydraulic systems that are available at NAPA. As I recall, they have a working pressure of 3,000 psig.

Rod

When human flesh is sprayed with hot oil under high pressure, it isn't pretty, and it is best to be absolutely sure of what the ratings are of the materials you are using, and allow a safe margin of error.