When to use a TSV on a water line

[daniellouw]

Hallo

I am designing a 3" line to supply raw water. The line is about 750 m long. The inlet pressure of the line is about 900 kPa(g) (9 atm) and the source is an open dam (thus the temperature is ambient temperature, between 5 and 30 deg C). The line can be isolated at the inlet and outlet. My question is: is it necessary to install a TSV (Temperature Safety Valve)?

I have looked in design manuals: One design manual state: "Relief valves shall not be provided for thermal expansion where piping and equipment can be blocked in between valves expect for liquid lines outside process areas (i.e. off sites). Protection against over pressure will be provided when low boiling liquids can be blocked in and the pressure can be increased due to vaporisation. These criteria should be considered as general rather than specific in regard to both location and application. Certain situations will arise that may require deviation from these norms." According to me, the water in this line will never reach boiling point, thus if I follow these guidelines, a TSV is not necessary.

I could not find anything in API 520 or 521.

I have spoken to my colleagues, but I got differences in opinions and neither of them were 100% sure.

I have also read through thread1203-149006 and thread124-133483: From these threads it is not 100% clear it I need a TSV. These are mainly how to size a TSV. However, from the threads, it seems as if I will need a TSV.

I got the compressibility of water at

http://www.ldeo.columbia.edu/~martins/hydro/lectures/proph2o.htm.

They specify it as: “An increase of pressure by 1 atmosphere (= 1013mbar = 14.7 psi) causes a decrease of the water volume by 5.3E-5 of the original volume”. According to my calculations, the pressure in the line can increase to 33106 kPa due to thermal expansion (if T1=5 deg C and T2=60 deg C and P1=900 kPa). Then a TSV will definitely be required.

As I say, it seems very likely that I will need a TSV. Can someone just please affirm that?

Thank you very much.

Daniel

 

[SeanB]

If the line can be blocked in full of liquid and the line is not insulated, then you definitely need a thermal relief valve.

 

[skoutso]

Your calculation for the pressure rise is correct. But you need a TSV only if the line can be shut-in. You can get rid of the TSV by carefully evaluating the chances of blocking-in the line.

If the line is not isolated there is no need for TSV.
If the line operates constinuously and it is isolated only for maintenance there is no need for TSV.
Check valves are not leakage free. Leakage through ordinary check valve is usually adequate to protect against overpressure from thermal expansion. An industry practice is to install a small by-pass with a check valve around the isolation valve. If the boundary valve is an ordinary check valve or if you have the above bypass installed, there is usually no need to provide TSV.

 

[daniellouw]

skoutso, the isolation valves will be gate valves or butterfly valves and not check valves, thus I assume that in that case, a TSV will still be required. But thanks for that information. You say that you don't need TSV's with check valves.