Piping Overpressure

[fefelvn]

Does anyone know what the guidelines are for piping ruptures i.e., at what pressure will piping rupture without a blocked flow condition (fluid with a open flow path to a low pressure rated vessel). I'm looking for a good resource on this subject. For example: 2000 psig gas flowing through 250 psig rated piping into a 250 design pressure vessel.

 

[BigInch]

First. It won't flow legally according to any design code I know of.

When the downstream outlet pressure plus the pressure drop of the flow through all the equipment is greater than or equal to the lowest burst pressure of any piece of equipment, you've found your maximum flowrate.... the hard way.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

I'd start with with a nice pressure drop per 100' of .5 to 10 PSI. I'd also look at the errosional velocities of the fluid and set a maximum speed of 3 to 100 ft/sec. These are wide ranges because it depends on how much energy you can waste, if the fluid has abrasive material, noise limits in the facility, but some general enough guidlines. THEN I'd size a valve to control the 2000 psig gas downto the 250 psig that the piping and vessel are good for.

I think the Crane TP 410 paper may discuss this.

 

[bimr]

You need to look into a piping handbook. Piping Handbook by Nayyar, McGraw Hill for example.

In the pipe design pressure formula, there is a Basic Design Factor F that takes into account the intended use and location of the piping. This design factor varies from 20% to 60% pressure derating. You have not provided enough information to get into any more detail.

 

[BigInch]

If you start with your equipment outlet pressure, assume a minimal flowrate, sum the flow losses of all equipment and iterate with increasing flowrates until the equipment inlet pressure reaches 250 psig, you'll get the most direct solution to flowrate. That way, the solution is not dependent on upstream piping or valves, where the rupture pressure and flowrates are whatever they are depending on wall thickness and yield or ultimate stresses.

bimr, "F" =1 when investigating yield hoop stress and "F" = ultimate_tensile_stress/yield, when investigating rupture hoop stress.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[jamesbanda]

I dont know the data for pipelines however I've seen the following guideance for vessels.

MAWP = Maxmum allowable working pressure. (ie design P)
P = 1* MAWP to 2* MAWP < Low probability of failure
P = 2* MAWP to 3* MAWP < Probable failure (0.5 chance)
P = 3 * MAWP > Near certain failure.

depending on the code you can replace the 3 with the 4.

Unless the pipe is overdesigned DONT SEND 2000 psig gas down the line YOU WILL FAIL THE LINE AND VESSEL

 

[djack77494]

I must be missing something, because this thread seems crazy to me. I'm reading/it is implied here that it is OK to exceed vessel and piping maximum allowable pressures by large margins. NO - Don't do it. You can hydrotest piping at above the design pressure and you can have a limited amount of accumulation in a pressure vessel during a relieving event above the design pressure, but these are well defined circumstances with well defined limits. In ordinary operations, you should never exceed your design conditions.

I know we've gotten pretty far off track from the initial question, but that question was quite confusing. What is the relevance of a connection to a low pressure vessel? Why specify that the outlet is not blocked? You may not get the responses you want because the presentation does not make sense.

Does that make any sense?
Doug

 

[BigInch]

Me too. Which is why I said you can't do it according to any code I know of.

But if he's trying to figure safety factor or something, that's legal engineering work. Wether he works for the US Army or Al Qaeda is not my business.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[dcasto]

Everyone agrees, no 2000 psi, if the limited piece is the pressure vessel, PSV set at 250 psig , finished. Size of valve is function of available flow, thermal, fire, tube rupture ect.... No one would recommend a puposeful overpressure without some protection.

We will leave the risk lawyers to sort out probability of failure and how much to pay orphans.

 

[bimr]

Have to agree with djack77494. Question does not make any sense.

Pressure is driving force. As Pressure decreases, gas expands and velocity increases. Temperature can increase or decrease depending upon relative effect of gas expansion and friction.

Rupture will occur at a fixed sonic velocity (the critical value) with mass flow influenced by the upstream pressure. Sonic velocity is approximately 1400 plus ft/sec.

 

[MJCronin]

fefelvn....

There are three commonly used formulas for calculating the burst pressure of seamless piping and tubing, Barlow’s formula, Boardman’s formula and Lame’s formula. Each uses the ultimate tensile strength of the material, at test temperature.

The formula that is incorporated into ASTM destructive test of piping is the Barlow formula, and is mentioned in the piping handbook.

Now, you should be aware that there are a lot of unknowns in burst testing of piping. Small defects and occlusions on the OD can affect the results. Variations in material properties and "out-of-roundness" can have an affect....

Testing of the same sample of piping will vary. Same with several other parameters.

The power piping code, ASME B31.1 allows a short time overpressurization of 20% if it occurs less than 1% ( as i recall) of the operating life.

Good luck..


-MJC

 

[sailoday28]

bimr (Civil/Environme)"Rupture will occur at a fixed sonic velocity (the critical value)..."
I don't understand your reasoning. Souldn't rupture occur at point where a specific pressure differential (inside to outside) occurs?
Also flow is not limited by sonic velocity for steady state gaseous flow. For isothermal flow (steady state)of a perfect gas the limiting Mach no = 1/sqrt(gamma) where gamma is the ration of Cp/Cv.

Regards

 

[BigInch]

I was waiting for that one.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[mfelzien]

BigInch - Not to make too many waves but got a chuckle out of your statement, "Wether he works for the US Army or Al Qaeda is not my business."

There is some wonderful satire on this. Tom Lehrers' song on "Wernher Von Braun". Very funny.. Wernher von braun makes the point that, "Where the rockets come down... thats not my department.. says Wenher Von Braun.".

 

[BigInch]

I'll remember that one.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com