Deflection of plastic pipe

[Kevin Chiu]

Hello everyone, I would like to ask about deflection limits for plastic piping.

I have a project where I used pipe stress analysis software to evaluate the stresses in a PPH pipe with a diameter of d160.

The simulation results show that the utilization is within the allowable limits. However, the calculated deflection is slightly higher than the DVS guideline (15 mm > 5 mm (L/150) ).

May I ask, if the stresses are acceptable but the deflection does not meet the guideline, what kinds of problems could this cause? Thank you for your feedback.

 

[GD2]

You need to evaluate what implication it will have by the process fluid on the piping. Where isolation and draining/ventings are required for maintenance and repair work, will it be safe to work? Think about a toxic material the piping is carrying. You may also encounter issues with gravity flow lines.
Talk to the process and take their opinion. It all comes down to safety.

 

[KevinNZ]

I have not seen a defection limit in any pipping code, just stress limits. Has DVS just made this up to be conservative?

 

[EngrPaper]

I have not seen a defection limit in any pipping code, just stress limits. Has DVS just made this up to be conservative?

Different codes have different standards. Even B31.1 when calculating its suggested maximum span uses a combination of a sag limit and a stress limit (Note C under table 121.5-1). In practicality, the engineering firms usually have internal standards for what is an acceptable sag for the sake of making span charts for the designers who are routing the pipe.

 

[LittleInch]

Add more supports.

Pipe like this doesn't like point supports and long term has a tendency to creep and sag.

Also next time don't assume we all know Gernan codes and standards...