ASME B31.3 Design Pressure Surge Vs Overpressure

[stanier]

B31.3 requires that the design pressure includes for surge at 301.2.2 b)In 302.4 f) 1) occassional variations are allowed up to 1.33 times design pressure.

Is it the intent here that the system should be designed such that the occassional loads do not create pressures that result in stresses above basic allowable. However in the event that there is a malfunction, unexpected event etc and the surge pressure doesnt not exceed that which creates stresses > 1.33 times basic allowable stress then the piping system remains in accordance with the Code? Given of course all the conditins of 302.4 are met.

For instance can one design a control system that keeps the piping operating inside the design pressure under surge conditions but if that control system failed or there was manual intervention then the system pressure could be allowed up to 1.33 times the design pressure.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[MJCronin]

stain,

It is normal and customary to consider the installation of a relief valve on piping systems to protect them against the extreme conditions where the pressure loading exceeds 1.33.

If the piping contains a liquid, a very modestly sized relief device can give a lot of protection....


MJC

 

[stanier]

Hi MJCronin,

Thank you for your reply but it doesn't address the question as such but raises an interesting point.

What pressure would you set the relief valve at? 110% of the design pressure or 110% of the occassional pressure (1.333 times design)?

Geoff

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au