PG-69.1.3 Capacity test data reports for each pressure relief valve design and size, signed by the manufacturer and Authorized Observer witnessing the tests, together with drawings showing the valve construction, shall be submitted to the ASME designee for review and acceptance.
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PG-69.1.4 Capacity certification tests shall be conducted at a pressure that does not exceed the set pressure by 3% or 2 psi (15 kPa), whichever is greater. Pressure relief valves shall be adjusted so that the blowdown does not exceed 4% of the set pressure. For pressure relief valves set at or below 100 psi (700 kPa), the blowdown shall be adjusted so as not to exceed 4 psi (30 kPa). Pressure relief valves used on forced-flow steam generators with no fixed steam and waterline, and pressure relief valves used on high-temperature water boilers shall be adjusted so that the blow down does not exceed 10% of the set pressure. The res eating pressure shall be noted and recorded.
PG-69.1.5 Capacity certification of pilot operated pressure relief valves may be based on tests without the pilot valves installed, provided prior to capacity tests it has been demonstrated by test to the satisfaction of the Authorized Observer that the pilot valve will cause the main valve to open fully at a pressure which does not exceed the set pressure by more than 3% or 2 psi (15 kPa), whichever is greater, and that the pilot valve in combination with the main valve will meet all of the requirements of this Section.
PG-69.1.6 Pressure relief valves for economizer service shall also be capacity certified using water at a temperature between 40°F and 125°F (4°C and 50°C). The pressure relief valves shall be tested without change to the adjustments established in PG-69.1.1 to PG-69.1.4.
PG-69.2 Relieving capacities shall be determined using one of the following methods.
PG-69.2.1 Three Valve Method. A capacity certification test is required on a set of three pressure relief valves for each combination of size, design, and pressure setting. The capacity of each valve of the set shall fall within a range of ±5% of the average capacity. If one of the three pressure relief valves tested falls outside this range, it shall be replaced by two valves, and a new average shall be calculated based on all four valves, excluding the replaced valve. Failure of any of the four capacities to fall within a range of ±5% of the new average shall be cause to refuse certification of that particular valve design.
The rated relieving capacity for each combination of design, size, and test pressure shall be 90% of the average capacity.
PG-69.2.2 Slope Method. If a Manufacturer wishes to apply the Code Symbol to a design of pressure relief valves, four valves of each combination of pipe size and orifice size shall be tested. These four valves shall be set at pressures that cover the approximate range of pressures for which the valve will be used or covering the range available at the certified test facility that shall conduct the tests. The capacities based on these four tests shall be as follows:
(a) The slope WIP of the actual measured capacity versus the flow pressure for each test point shall be calculated and averaged
For steam
For water
All values derived from the testing must fall within ±5% of the average value:
minimum slope = 0.95 x average slope
maximum slope = 1.05 x average slope
If the values derived from the testing do not fall between the minimum and maximum slope values, the Authorized Observer shall require that additional valves be tested at the rate of two for each valve beyond the maximum and minimum values with a limit of four additional valves.
For steam applications the relieving capacity to be stamped on the valve shall not exceed 90% of the average slope times the absolute accumulation pressure
rated slope = 0.90 x average slope
For water applications the relieving capacity shall not exceed 90% of the average slope multiplied by the square root of the difference between the flow rating pressure and the valve discharge pressure.
(U.S. Customary Units)
stamped capacity ≤ rated slope (1.03 x set pressure + 14.7) or (set pressure + 2 psi + 14.7), whichever is greater
(SI Units)
stamped capacity ≤ rated slope (1.03 x set pressure + 0.101) or (set pressure + 0.015 MPa + 0.101), whichever is greater
PG-69.2.3 Coefficient of Discharge Method. A coefficient of discharge for the design, K, may be established for a specific valve design according to the following procedure:
(a) For each design, the pressure relief valve manufacturer shall submit for test at least three valves for each of three different sizes (a total of nine valves). Each valve of a given size shall be set at a different pressure, covering the range of pressures for which the valve will be used or the range available at the facility where the tests are conducted.
For each valve design where the coefficient of discharge has been determined that is intended to be restricted in lift, the Manufacturer shall have capacity tests conducted on three valves of different sizes. Each size valve shall be tested for capacity at the minimum lift for which certification is required, and at two intermediate lift points between the full rated lift and minimum lift certification points. Each of the three test valves shall be set at a different pressure.
For each valve tested, it shall be verified that actual measured capacity at restricted lift will equal or exceed the rated capacity at full rated lift multiplied by the ratio of measured restricted lift to full rated lift.
(b) Tests shall be made on each pressure relief valve to determine its lift at capacity, popping, and blowdown pressures, and actual relieving capacity. An individual coefficient, K
D, shall be established for each valve as follows:
Where actual flow is determined by test and theoretical flow, WT is calculated by one of the following equations:
For tests with dry saturated steam
For 45 deg seat
(U.S. Customary Units)
WT = 51.5 x pDLP x 0.707
(SI Units)
WT = 5.25 x pDLP x 0.707
For flat seat
(U.S. Customary Units)
WT = 51.5 x pDLP
(SI Units)
WT = 5.25 x pDLP
For nozzle
(U.S. Customary Units)
WT = 51.5 AP
(SI Units)
WT = 5.25 AP
For tests with water
For 45 deg seat
(U.S. Customary Units)
(SI Units)
For flat seat
(U.S. Customary Units)
(SI Units)
For nozzle
(U.S. Customary Units)
(SI Units)
where
A = nozzle throat area, in.2 (mm2)
D = seat diameter, in. (mm)
L = lift at pressure P, in. (mm)
P = (1.03 X set pressure + 14.7), psia, or
= (set pressure + 2 + 14.7), psia, whichever is greater
= (1.03 X set pressure + 0.101), MPa, or
= (set pressure + 0.014 + 0.101), MPa, whichever is greater
P d = pressure at discharge of the valve, psia (MPa)
WT = theoretical flow, lb/hr (kg/hr)
w = specific weight of water at inlet conditions, lb/ft3 (kg/m3)
To convert lb/hr of water to gal/min of water, multiply the capacity in lb/hr by 1/500, To convert kg/hr of water to liter/min of water, multiply the capacity in liter/min by 1/60.
The average of the coefficients KD of the nine tests required shall be multiplied by 0.90, and this product shall be taken as the coefficient K of that design. All individual coefficients of discharge, KD, shall fall within a range of ±5% of the average coefficient found. If a valve fails to meet this requirement, the Authorized Observer shall require two additional valves to be tested as replacements for each valve having an individual coefficient, KD, outside the ±5% range, with a limit of four additional valves. Failure of a coefficient, KD, to fall within ±5% of the new average value, excluding the replaced valve(s), shall be cause to refuse certification of that particular valve design.
The rated relieving capacity of all sizes and set pressures of a given design, for which K has been established under the provision of this paragraph, shall be determined by the equation:
W ≤ WT x K
where
K = coefficient of discharge for the design
W = rated relieving capacity, lb/hr (kg/hr)
WT = theoretical flow, defined by the same equation used to determine KD, lb/hr (kg/hr)
