Design Pressure and Temperature

Can you explain your questions clearer as I am not sure what your asking.

What is your application?

The process piping system am working with has an operating pressure of 2600 PSI. I need to find out what the design pressure of the system is. What factor (value) can I multiply with the operating pressure to have my design pressure.

In similar situation, what factor will be multiplied by operating temperature to give design temperature.

If you make the design pressure and temperature at least = to maximum operating pressure/temperature I don't think you'll go far wrong. This approach is used for pressure vessel design. The designer then works to that. There are safety factors in the design codes which ensure the material is well below ultimate tensile stress at design conditions.

As it's a pipe, you don't need to design it specifically (though somebody must have done it at some point), as pipe comes in pressure/temperature ranges depending on wall thickness (for a given diameter). Just need to select pipe with adequate rating. Same goes for pipe connections.

Cheers........Codey

It is impossible to answer your question. Your location is unknown as is your competence. But, from the details provided, I doubt that we can help.

That is correct - we cannot give you a definite answer.

It should depends on company standards.

Which involves future expansion considerations, pumping deadhead pressure, effects/anticipated hammering, tie-ins to existing equipment (pressure vessels, existing relief valves, ...) ........

I have seen values of 10% higher, more commonly 15%, sometimes 25%, less commonly 50% (when expansion considerations drove the installation)

Same goes for temperature.

lynlynch your compentence, or rather lack of is well know and well documented. Not really sure what the location has to do with supplying a general answer. Once more you post just for the sake of it. sad really

The top end burst pressure requirements may be many times higher than the designed working pressure also depending on the shock loads.

Hydraulic systems often work on the 2000 -3000 PSI range with temperatures up to around 200 F. The design of most hydraulic line systems now are for working pressures 2 - 3 times the system relief pressure and with burst ratings 2 - 4 times higher than the lines rated working pressure ratings!

Its common to use 4500 - 6000 PSI working pressure rated hoses on a 2000 - 3000 PSI system. And the good quality 4500 - 6000 PSI rated hose typically has burst ratings of around 3:1 - 4:1 or around 13500 - 24000 PSI!

I was recently working for a farmer who had four brand new hydraulic lines burst in a very short time frame all on similar load applications. (truck and trailer hoist systems) The trucks are rated as having 2000 PSI pump systems. The hoses were rated at 2400 PSI with a 2:1 burst rating. The simple shock load of moving the hydraulic levers quickly with loads on them was enough to burst them. (grain and beet elevators and pilers really don't like having 20 -30 gallons of hydraulic oil sprayed all over their facilities and equipment. I know, I burst one on a beet piler and OH what a mess!)

Now all the trucks and trailers with that line are going to have to be taken apart and have it replaced with 6000 PSI line with a minimum burst rating of 3:1.

I don't know if that helps you any but as you can see just by application and working conditions you may have to have far higher limit capacities than you may have first assumed. If the fluids being pumped at high pressures and tempuratures are dangerous and people are going to regularily need to be working any where near them there may be even higher levels of safe overhead working and burst pressures required as well.

Have a look to swagelok. It's a company that sell tubing. Their tubing data is on the net (i.e. http://www.swagelok.com/downloads/webcatalogs/EN/MS-01-107.pdf). It might give you more understanding about your question. From what I know their product are very reliable, since they use a factor of 4 for their suggested allowable pressure, meaning that they divide by 4 the maximum pressure in order to get the allowable pressure. In this link (i.e pdf format) you would also get the factor by which you should multiply in order to get the allowable pressure for a particular maximum temperature. Having said that you should not apply those number to tubing that are not from that company. Since those number comme from leak test, you should get the number from the company that made your pipes systems.

What code are you using?

It is recommended in all standards that maximum operating pressure shall be taken as design pressure to calculate the wall thickness. You have also to consider the maximum operating temperature as design temperature in order to find the allowable stress values of the material you have chosen. You must also consider if any additional force other than operating pressure is applying on the walls of the pipe, water hammer forces for example. If you have any surge loads such as water hammer forces you have to follow the below steps:

1. Find out the wall thickness as per design pressure
2. Check out if the stress for the selected wall thickness, including the surge loads, are below the yield point of the material. You must be always below the yield point ( for stress with surge load appr. 87% of the yield point)
3. If the wall thickness is not sufficient for surge loads increase the thickness.

As others have posted the factor you select is based on numerous factors. My experience with piping selection is based on industrial hydraulic systems. As you have not stated the application clearly I will base my response on generally accepted practice for piping selection for industrial hydraulic systems though the selection process is similar for other applications. I will assume you are attempting to determine what schedule of pipe to select. You are then also trying to determine the pipe size for acceptable flow/pressure losses over the system run length.

As the pipe size goes up for a given schedule the pressure rating goes down. If you go to the next heavier pipe schedule the I.D (inner diameter) gets smaller so you must again consider the acceptable pressure drop. Don't forget to include additional pressure drop for t's and elbows etc.

Standard Pipe Tables may provide "Working PSI" others will provide "Max Pressure". They will almost always also provide "Burst Pressure" The factor between working and burst is conservatively set at 6:1 between burst and working pressure. You can go lower 4:1 is commonly used as well. "If in doubt make it stout" Take care though as If the application will allow the piping to be exposed to

corrosion

puts human life at risk,

high cycling (pressurized to de-pressurized)

high shock due to water hammer or external shock loading of actuators

or leaks are expensive to contain (ie are you close to waterways etc)

You will want to stay closer to the 6:1 range or higher

If the application is low risk, has smooth pressure rise, low number of pressure cycles, doesn't pose significant risk to people and is in a contained area. You could go lower than 4:1 but I would not go lower than 2:1 under almost any circumstances even at that level you need to be really sure that is what you want to do. Of course this all leads back to dollars. The higher the factor the more costly the installation. Make sure all stakeholders are involved with the decision on what factor to use and sign off if a lower factor is selected. You save money now but could be in major trouble later.

There may be a factor that is required based on the application type. If for example it is for a marine application you will have to investigate the standard being designed to DNV (Det Norske Veritas) or Lloyd's for example.

You can find Pipe and Fittings tables on the internet but I would try to get them from the vendor you plan on sourcing them from.

Have fun.

My background is in Process design - typically we wouldnt set design conditions for pipework. The design conditions for the pipework would be copied forwards or back from the vessels at either end or the pump / compressor

For a pump I would always specify the downstream system for the shut in head of the pump - the calculation of this depends on the variation between normal and design pressure in the suction vessel, the proportion of head due to static losses and dynamic losses, the shape of the pump curve and the overall head gain.

For a vessel the start point would typically be to add 10% to the highest possible working pressure that is if the system cycles or is operated in different modes whichever one gives the highest. If there is no intended variation it is prudent to add 5% to the specified normal to allow for some variation so overall you add 15%.

However many vessels have odd design pressures (ie much higher than their working pressure) due to such things as settle out from compressors etc.

For temperatures it is normal to ADD a temperature margin 20°C (36°F) is typical to all ow for variation. Again there might be circumstances where you would choose not to do this. e.g. For a steam vessel, LPG service you might set the Design Temp in line with the vaporisation temperature at the design pressure with say 10°C margin.

If temps are based on ambient conditions remember to use the black body temp for the site not the max ambient. On a project in Kuwait the max ambient is 52°C but the black body temp (ie the temp of materials left in the sun) is 82°C and this is the max design temperature even for refrigerated systems operating at -45°C

Without knowing what the design standards relevant to the facility are, it is not possible to help.

Check the design standards and consult a local Mentor within the organisation, because these pressures are not the sort of thing that needs to be handled by a novice; ask for appropriate training as a first step.