4 | Baker Hughes
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Jacket Pressure Set Point
pressure for a required flow
rate can now be determined
by either of two methods:
Do not exceed the maximum rated diffential pressure
of the Tube at any time.
A. Tube Differential chart adjustment method:
Example:
1. A 12”, ASME Class 600, 887 Surge Reliever, with a
Nitrile 846 Tube is connected into a pipeline where
the fluid (water) is just above freezing, 32 degrees
Fahrenheit.
2. The pipeline pressure that is to be protected is
approximately 800 psig (55 barg).
3. The Maximum Allowable Operating Pressure (MAOP)
is 1440 psig (99.3 barg).
4. The 887 is to start opening and relieve pipeline
pressure at 900 psig (62 barg), this is the Designed
relief pressure.
5. Refer to the REDQ Tube Differential Pressure Chart to
select the DF Min and DF Max. values using the valve
size, the Tube/Durometer, the ASME Class, and the
lowest estimated operational temperature of the tube:
i. DF Min = 23 psid (1.6 bard)
ii. DF Max = 41 psid (2.8 bard)
6. Determine the Jacket Pressure Set Point: Subtract
DF Min from the pressure determined in item 4. of this
example, the Designed Relief Pressure… 900 psig – 23
psid = 877 psig (62 barg - 1.6 bard = 60.4 barg) .
This is the Jacket Pressure Set Point pressure reading
for the pressure gauge connected to the Jacket Port
connection.
7. Determine the pressure the 887 Surge Reliever will
be fully open: Add DF Max to the Jacket Pressure Set
Point pressure…41 psid + 877 psig = 918 psig (2.8 bard
+ 60.4 barg = 63.2 barg).
This is the approximate pipeline pressure where the
887 surge reliever will be fully open (918 psig).
8. Verify the Jacket Pressure Set Point pressure will
remain constant enough for the application.
B. Direct flow adjustment: Jacket pressure is directly
adjusted to attain the required flow rate at the desired set
point.
Example:
1. Desired relief point is 900 psig (62 barg) at a flow rate
of 1000 GPM (0.063 m3/s).
Do not exceed the maximum rated differential pres-
sure of the Tube at any time.
2. Introduce Jacket pressure of 950 psig (65.5 barg) with
a dry gas.
3. Introduce inlet line pressure of 900 psig (62 barg).
4. Reduce the Jacket pressure slowly until flow just
begins; record the Jacket pressure (assume 877 psig or
60.4 barg)… Inlet pipeline pressure – Jacket Pressure
Set Point pressure just flowing or - 900 psig - 877 psig
= 23 +/- psid = DF Min. (62 barg - 60.4 barg = 1.6 bard
+/- barg = DF Min.).
5. Continue to reduce the Jacket Pressure Set Point
pressure slowly until flow of 1000 GPM (0.063 m3/s) is
attained; record the Jacket Pressure Set Point pressure
(assume 870 psig /60 barg), approximately 900 – 870 =
30 +/- psig (62 - 60 = 2 +/- barg).
6. With the Jacket Pressure Set Point pressure set at
870 psig/60 barg. The 887 valve will flow 1000 GPM
(0.063 m3/s) when the pipeline pressure reaches
approximately 900 psig = (870 psig + 30 psig) or 62
barg = (60 barg + 2 barg).
