Sulphuric acid TRV 1

[leo31]

Hello there, I'm trying to help with a side project following up a training HAZOP analysis where it's has been underlined how a PSV might be necessary for a loading pipeline where fluid might get trapped and be effected by solar heat. The fluid is diluite sulphuric acid (at different concentration depending on the request).
By looking at the Total Pressure of Aqueous Sulfuric Acid Solutions I've gathered that no vaporization of the solution has to be expected as the pressure would have to be too low.

By reading some very interesting threads here I understood how in this case a TRV should be required, so I've tried to evaluate what thermic expansion is to be expected to then understand what overpressure could be developed.

At this point I've calculated the cubic expansion coefficient α=0,0006 1/°C (both by hand and also by finding tabulated values) and also the isothermal compressibility coefficient X=3*10^-5 1/bar. By putting this informations together i get ΔP/ΔT=19 bar/°C so with only 1°C the pressure would increase of 19 bar, way higher than the 5 bar design pressure of the pipes.

Could this be correct ? Should i stick with the TRV or should I get a look into a proper PSV ? Many thanks in advance

 

[mk3223]

Yes, the TRV is typically installed in the loading/unloading pipeline to protect it from overpressure due to the liquid thermal expansion as exposed under the sun.

 

[LittleInch]

19 bar per C seems a bit high but I wouldn't surprised at between 2 and 4 bar / C

But volume will be very small hence the TRVs are very small.

See this FAQ which might help

https://www.eng-tips.com/faqs.cfm?fid=1339

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[leo31]

Thanks for your answers, I'll have get a look into this and check my results

 

[LittleInch]

You need to find bulk modulus of the fluid.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[shvet]

@leo31
I bet at final you will obtain results that TRV's orrifice area required is less than the smallest one manufactured&distributed by local suppliers and any commercially available industial RV is ok for this application.

Why not just add a simple gas pocket?

4.4.12 Hydraulic Expansion
4.4.12.2 Sizing and Set Pressure
The required relieving rate is not easy to determine. Since every application is for a relieving liquid, the required relieving rate is small; specifying an oversized device is, therefore, reasonable. A nominal diameter (DN) 20 × DN 25 (NPS 3/4 × NPS 1) relief valve is commonly used. If there is reason to believe that this size is not adequate, the procedure in 4.4.12.3 can be applied.

302.2.4 Allowances for Pressure and Temperature Variations.
...
(f) Occasional variations above design conditions shall remain within one of the following limits for pressure design.
...(1) Subject to the owner’s approval, it is permissible to exceed the pressure rating or the allowable stress for pressure design at the temperature of the increased condition by not more than
......(-a) 33% for no more than 10 h at any one time and no more than 100 h/y, or
......(-b) 20% for no more than 50 h at any one time and no more than 500 h/y
The effects of such variations shall be determined by the designer to be safe over the service life of the piping system by methods acceptable to the owner. (See Appendix V.)
(2) When the variation is self-limiting (e.g., due to a pressure-relieving event), and lasts no more than 50 h at any one time and not more than 500 h/y, it is permissible to exceed the pressure rating or the allowable stress for pressure design at the temperature of the increased condition by not more than 20%.

 

[Latexman]

For most ambient heated lines within the "battery limits" of a process area or loading/unloading operation, there is no need to size the PSV. Just install a 3/4" or 1" TRV. An example where calculations for thermal expansion generated by ambient heating should be considered is applications (e.g. long pipelines or large liquid-filled vessels) where the required flow rate due to thermal expansion approaches the rated capacity of the valve. This is where experience helps us; knowing intuitively when the problem is too big for the 3/4" or 1" TRV.

dP/dT of 19 bar/[sup]o[/sup]C tells us nothing about the size of the problem. More details/better description from you will allow us to help make a determination if the PSV needs to be sized or not. What kind of loading pipeline? Ship, railcar, truck, other? Loading pipeline diameter and approximate length? Is the pipeline insulated or bare? Is the pipeline painted or not; what color? Location of installation?

Good Luck,
Latexman