Sch 40 vs Sch 80

[phllp581]

Can you mix Sch 40 and Sch 80 pipe/fittings? For example I am having a hard time finding 3/4" Sch 40 API 5L FBE Seamless pipe, but I can find Sch 80, Is it okay to upgrade to Sch 80 and intermix with Sch 40, or will the fittings and pipe not connect properly?

 

[bimr]

The outside diameter remains the same regardless of schedule. Schedule 40 and schedule 80 pipe use the same fittings and same points of entry, making them interchangeable in jobs that don’t require a heavier walled pipe.

 

[pennpiper]

Schedule 80 fittings will mate with Sch 40 pipe. The only issue is the I.D. of the two will not match absolutely. But in the sizes you are talking about (3/4") it is probably not a problem as long as your flow rates are low and the service is not a slurry.

Sometimes its possible to do all the right things and still get bad results

 

[BigInch]

Welding wall thicknesses of 3/32"+ (2.38mm) will require special taper cut or a transition piece under some codes.

 

[moltenmetal]

If you're butt welding the parts, you should not mix wall thicknesses. Even if you properly back-taper the bore, you are likely to fail radiographic examination- not due to real problems, but due to problems of interpreting the radiographs.

If you are socket welding, which would make the most sense at 3/4" NPS in most services, then the pipe wall doesn't matter - assuming the lighter wall is adequately strong for the service.

 

[racookpe1978]

In general, yes, you can replace a lighter weight fitting with a heavier schedule fitting.
You can replace a light weight (thinner wall) pipe like Sch40 with its heavier-walled same-dia Sch80, same material for most welded fittings - butt weld prep's need to be addressed as mentioned above.

BUT! Flanges are different: You can generally use a heavier-walled pipe within a pipeline or a pipe run (make sure you update the as-built configuration record appropriately for that section) if the specified flanges mounted outside the pipe remain the same. You CANNOT arbitrarily replace lower-rated flanges with heavier-rated (higher-rated) flanges since the bolt holes, gaskets, bolt lengths and diameters, and flange faces will then differ.

 

[pennpiper]

Hay folks the original question only referred to 3/4" piping, let's not go overboard.

Sometimes its possible to do all the right things and still get bad results

 

[pryn12]

Yes, you can use higher schedule pipe always. Just have to make sure the velocity should not exceeds above. As far as 3/4" pipe concernd, there will be 2mm difference between both schedule which is actually less than 10%. I believe it should be fine. Please bore the pipe to suit the id of sch.40.

 

[XL83NL]

Keep in mind your stress analysis, if performed, may have a different outcome. Sch80, though thicker and often considered to be stronger by most people, is less flexible and easily induce higher thermal displacement stresses, which can be detrimental (though I doubt if this would be the case for 3/4"). I once ran into the situation where sch10 wasn't available and we had to use sch20. The (negative) impact on the stress analysis was there for sure.

 

[BigInch]

Don't usually do stress analysis on such tiny line diameters.