Dear All

Greeting.....

I want to calculate relief quantity due to solar radiation only. In this case i required area which is exposed to solar radiation. According to me area will be foot print area. Area (A) = Line Outer Dia (D) x Length (L) between two valve. Although the value of the solar radiation is generally in the range of 250 to 330 BTU/hr/ft2 (0.79 to 1.04 kW/m2). as per API 521, Pg. no. 41. In this case total total heat transfer rate will be = Foot print area x 330 BTU/hr. (maximum). Accordingly we can calculate capacity.
My reservation is, in actual semi cylinder exposes the solar radiation, in any case the exposed curve surface area does not more than half because solar radiation will be only one side even vertical pipe or tilted from y axis, in this case the half curve surface area will not be equal to foot print area then curve surface area will be = 3.14xDxL/2. But in this case the solar radiation will not be equal to every point on the curve surface area and radiation will be maximum only on perpendicular to the sun so we can not take 330 BTU/hr/ft2 value for whole curved surface area. So better to take foot print area. Although it will not make much difference in relief capacity. In API 521 page 13,14 The total heat transfer rate (H) BTU/hr. For calculating H, API considered volume expanded by the solar radiation due to radiation , conduction and convection, but i am not sure for the conduction which area they have taken, whether foot print or semi cylinder.

Your's comment will be always expedite.

With Regards

Sunil Pal
EEC, Mumbai

Why do you want to calculate the relief quantity due to solar radiation only?

And what is it that you are calculating? Is it a pipe? Is it a 100% liquid-full vessel?

Is this a thermal relief valve application?

If it is a thermal relief application, you normally do not have to calculate anything. Simply install a conventional 1/2" or 3/4" diameter thermal relief valve and you're done.

Please explain what it is (or what you think) that you are confronting.

It's vendor requirement, Vender does not accept Material Requisition (MR) for the Thermal expansion relief valve without relief quantity. However 1/2" or 3/4" is the inlet size of the of the pipe and for the calculation of orifice area we have required relief quantity. I admit mostly the valve size 3/4" or 1/2" inlet but being a design engineer, it does not necessary the valve always will be 1/2" or 3/4" only. After the calculation whatever quantity comes the size should be based on that. API does not says that for the thermal radiation due to solar radiation for sizing the valve relief quantity is not required. Primiraly this problems comes in pipe only. In the last post we have calculated for consideration of pipe.
In same time without relief quantity, we can not find out the number of devices if the line is having higher dia and long length or we can not justify provided valve adequate or not.
Yes , this is thermal relief valve application.

Sinil:

I don’t know what “MR” means, I only speak English, Spanish, Portuguese, and some French.

You say it’s a thermal relief application; then, it only requires a nominal ½” or ¾” thermal relief valve. That, in USA practice is the accepted, legal engineering norm. I don’t know what the requirements are in India. We don’t calculate the relief quantity here in the USA, and much less the relief rate.

If you look at the size (volumetric capacity) of your “equipment” – which you don’t identify – you will probably find out that the theoretical relief quantity due to radiation is probably so small (a few cm3/min) that a formal calculation is considered a ridiculous waste of time. However, we don’t know the size of your “equipment”, so there is a remote possibility that you may have need for a larger relief valve or rupture disk.

@Sunil Pal

It is still not clear if you are talking about the thermal relief for a pipe, pipe line or for equipment. Please clarify.

For pipes that are not considered pipelines of considerable length and diameter, and considering only solar heating, then I will disagree with you, a 3/4" x 1" PSV will always be more than ample for protection. As Art said, you are not required (at least in the U.S.) to show a calculation to prove this. The orifice calculated from the required relieving rate will not even come close to the smallest PSV you can buy so why bother? If you want or need to consider fire, then yes, you can possibly require a significantly larger PSV than the 3/4" x 1".

If you are so intent on calculating the heat requirements, then you only need to grab a copy of Perry's Chemical Engineering Handbook. I believe there is a procedure given for solar heating.

I don't understand your vendor as they are not responsible for determining the PSV size required, you are. They should supply what you ask for. If your vendor insists on a relief capacity and to save you some time, then take the stamped capacity of the particular 3/4" x 1" PSV you want to purchase and use that.

You also have to understand what is happening here and why you want a PSV for thermal relief in the first place. If the pipe is completely full, there is no place for liquid to go whan it begins to increase in volume as the temperature goes up. Liquid expansion is very slight but creates a tremendous amount of pressure when it does expand. The PSV allows a certain amount of liquid to burp out of the pipe. Once this "burp" happens, the pipe is no longer completely full. Therefore, the odds of a second relief happening is essentially nill after this since the liquid will not expand enough to refill the pipe. This is why for a scenario such as solar heating can be protected with just a minimum 3/4" x 1" PSV.

Greetings to all.

The following may be used to approximate relieving rates of liquid expanded by thermal forces where no vapor is generated at relief valve setting and maximun temperature. These calculation assume the liquid is non-compressible:

gpm = ( B )( Q )/500(G)(S)

typical values of the liquid expansion coefficient B are:

API Gravity*********Specific Gravity*********B, 1/ºF
water***************1.000****************0.0001
3 - 34.9*************1.052 - 0.850**********0.0004
35 - 50.9************0.850 - 0.775**********0.0005
51 - 63.9************0.775 - 0.724**********0.0006
79 - 88.9************0.672 - 0.642**********0.0008
94 - 100*************0.628 - 0.611**********0.0009

Q, BTU/hr = solar radiation (250 - 330 BTU/hr * sq ft) aplied to surface area
G = specific gravity relative to Air=1.0 or water=1.0
S = Specific heat (BTU/lb ºF)

I hope that this information help you. usually this value is accepted for completed the MR's

JULYSAN,
Good information...

The formula seem to me was extracted from API RP 1997.

I hope you are using latest API Std 521 Fifth edition, 2007.

JoeWong

Hi

I am using API 521 2007 ed

I have been asked to justify installing a thermal expansion relief valve in a gas condensate line

I have therefore tried to use equations 3, 4 & 5 to determine the increase in pressure if the line becomes boxed in.

However, the formulae do not converge

I have tried this graphically also

Has anyone had this problem?

Regards

Ian

eqns from section 5.14.4

Mr. Art,
I agree with you. I have several TSV in our gathering pipeline (2 phase, gas and liquid), it is D orifice size. Problem is, I was requested to design a relief system to receive any relief from those TSVs? Does anyone has any experiences on how to designed a relief system for TSV? Should we provide a kind of vessel or can we release it to atmosphere?
Thank you,

Witono
- Indonesia -