Iranian Classification Society Rules

Section 14 Safety Valves

1401. Application

The requirements in this Section apply to tests and inspection for the type approval according to the following:

(1) The approval of the coefficient K in the calculation formula of the discharge capacity of safety valves of boilers (excluding the ordinary type valves, hereinafter the same in this Section) based on Pt 5, Ch 5, 123. of the Rules.

(2) The approval of the blow-off coefficient K in the calculation formula of the blow-off rate of pressure relief valves of the cargo containment system and process pressure vessels according to

Pt 7, Ch 5, 802. 5 of the Rules.

1402. Data to be submitted

The sectional assembly drawings of the safety valve are to be submitted to the Society in addition to those specified in 102.

1403. Type tests

1. Test

(1) The test is to be carried out according to one of the following (a), (b) and (c). The test fluid

is to be steam, air or gas having known property and the fluid atmosphere.

(A) Test A: For the same design series (e.g., the group having

at back pressure side is to be

serial nominal diameter to the

nominal pressure), the 3 representative nominal diameters are ent pressure. The 9 actual blow-off rates are measured and determined.

chosen and tested by 3 the blow-off coefficient

differ-

(K) is

(B) Test B: For the same design series, the 4 representative nominal diameters are chosen

tested by different pressure respectively. The actual blow-off rate is measured and blow-off coefficient (K) is determined.

and the

and

tested by same pressure. The actual blow-off rate is measured

(K) is determined.

and the blow-off coefficient

(2) Gauges and measuring procedures are to

3.14.1

be in accordance with the requirements given in Table

Table 3.14.1 Gauges and measuring procedures

measuring item	measuring procedures
Atmospheric pressure	Atmospheric pressure is to be measured by the gauge with error range of 33.3 Pa or less.
Temperature	Temperature is to be measured by the calibrated thermocouples or resistance thermometer in the in- side of pipes or thermometer case with attention to thermal conduction and radiation.
Pressure	The static pressure not more than 0.1 MPa is to be measured by manometer, and the static pressure over 0.1 MPa or differential pressure is to be measured by a calibrated Bourdon pressure gauge.
Flow rate	The orifice or nozzle according to national standard, etc., is to be used to measure flow rate, and the choking diameter ratio of orifice to pipe is to be not more than 0.7. The differential pressure be- tween before and after orifice is to be 100 ~ 2,500 mm H2O, and the test is to be carried out in a steady flow condition (for fluctuation over 2 %, the cause is to be checked and calibrated).
Head	The head is to be measured by calibrated 0.01 mm level dial gauge, and the head limiting device is to be attached at the valve stem to prevent exceeding design head.
Steam condition	(a) The temperature, pressure and humidity of steam in the safety valve inlet and atmospheric pres- sure are to be measured. (b) The humidity of steam is to be measured by well-insulated reducing type calorimeter and ther- mometer after reducing pressure. However, the measurement is not to be applied to steam hav- ing more than 10 % humidity. And the superheating of superheated steam at outlet of calo- rimeter may be 4.5 °C or over.

Guidance for Approval of Manufacturing Process and Type Approval, Etc. 2015 97

Table 3.14.1 Gauges and measuring procedures (continued)

measuring item	measuring procedures
Steam condition	(c) The humidity of steam is to be obtained from diagram or the enthalpy obtained from the following formula according to the steam table. Humidity (%) = 100 - where, : Dryness(%), ′ × : Enthalpy of superheated steam at atmosphere and steam temperature meas- ured by choking type calorimeter (kcal kg) ′ : Enthalpy of saturated water at steam pressure measured at inlet of choking type calorimeter (kcal kg) : Evaporation heat at steam pressure measured at inlet of choking type calo- rimeter (kcal kg) (d) The temperature measured by choking type calorimeter is not to have a difference of 0.5 °C or over at normal condition.
Air condition	The air temperature and pressure at safety valve inlet are to be measured, and the air is to be free from dust and oil.
Gas condition	The measurement of gas condition having known property is to be carried out according to the air condition measurement above.

measuring item	measuring procedures
Test apparatus	(a) Test apparatus is to be able to warm up insulated parts of the apparatus and pipes sufficiently and provided with a drain valve in its lowest part. (b) Test apparatus is to be provided with a pressure gauge, a thermometer and a head measuring de- vice at safety valve inlet. When using saturated steam, reducing type calorimeter is to be fitted for steam humidity measurement.
Test preparation	Before the test, the drainage in test apparatus is to be fully discharged.
Test of valve	(a) The pressure at safety valve inlet is to be maintained to the pressure for decision of blow-off rate until each gauge being steady state. (b) The pressure at valve inlet, indicating value of flow meter, head of valve and steam temperature and humidity are to be measured when each gauge is in a steady state.

(3) Test procedures by steam is to be in accordance with the requirements given in Table 3.14.2 Table 3.14.2 Test procedure by steam

measuring item	measuring procedures
Test apparatus	(a) A drain valve is to be fitted in the lowest part of the apparatus or pipes and is to be observed for occurrence of frost in the test. (b) Pressure gauge and thermometer for measurement of air at safety valve inlet and head measuring apparatus are to be fitted.
Test preparation	Before the test, the drainage in test apparatus is to be fully discharged.
Test of valve	(a) Pressure at the safety valve inlet is to be maintained to the pressure for determination of blow-off rate until each gauge is in a steady state. (b) The pressure and temperature at the valve inlet, indicating value of flow meter and head of valve are to be measured when each gauge is in a steady state.

(4) Test procedures by air is to be in accordance with the requirements given in Table 3.14.3 Table 3.14.3 Test procedure by air

(5) Determination of blow-off rate and nominal blow-off coefficient (K)

98 Guidance for Approval of Manufacturing Process and Type Approval, Etc. 2015

(A) The condition for determination of blow-off coefficient

(a) The measured value, in order to evaluate blow-off coefficient (K), is to be compensated for gauge error, and not to be much fluctuation.

(b) In case test fluid is humid saturated steam, the measured value is to be compensated for humidity.

be selected in large range as practicable.

(d) Each blow-off coefficient (K') obtained from measurement of actual blow-off rate is to be within a range of ± 5 % of their average value.

(e)

The measurement of actual blow-off rate is, in principle, to be carried out one time in

(f)

1 test condition, and if there is any doubt about the measured value, measurement may

be added 2 times in same condition. The measured value K in this case is to be used for the evaluation of (d) above. However, if (d) above is not satisfied, the corrected safety valve or substitute of the same design condition may be tested additionally.

The standard deviation of actual blow-off rate obtained from (B) (a) above is to be not more than 2.5 %.

(B) Determination of blow-off rate and blow-off coefficient

(a) Determination of blow-off rate by reducing apparatus

(i) The measurement of blow-off rate by reducing apparatus is to be in accordance with

(2) above, and in principle, to be calculated by the following formula, and may be determined by other national standard.

where,

: Flow rate at orifice inlet(kg/h)

: Flow rate

Reduced hole diameter in operation state (m)

: Pressure difference between before and after orifice (Pa)

∆ Fluid density at orifice inlet (kg m ), for air, ×

× ×

: Absolute temperature of fluid at orifice inlet ( )

(ii) The calculated flow rate is to be considered for standard deviation which may be obtained according to the requirement of 3.6 of KS A 0612 or equivalent.

(b) Theoretical blow-off rate formula

Theoretical blow-off rate is to be determined by the following formula (i) or (ii).

(i) Case of calculation with assumption that ideal gas having frictionless flow in safety

valve, flow coefficient of 1.0 and constant specific heat having isentropic process is blow-off.

× ×

However, in case of

≤

× ×

Theoretical blow-off rate (kg/h)

Guidance for Approval of Manufacturing Process and Type Approval, Etc. 2015 99

Actual blow-off area of test valve (mm )

: Adiabatic exponent of fluid at valve inlet, for air, may be

1.40. Absolute pressure at valve inlet (Pa)

Absolute pressure at valve outlet (Pa)

: Specific volume of fluid at valve inlet (m

kg)

: Gas constant of fluid (J/(kg K))

(ii) Case of absolute pressure at valve outlet not much more than critical absolute pres- sure at valve inlet for steam or gas

(steam) ×

where,

: Molecular weight of gas (kg/h)

Actual blow-off area of test valve (mm )

: Steam pressure at valve inlet (MPa gauge)

Factor depending on steam property according to the requirement of

KS B 6352

4.2.2 of

(gas)

where,

: Molecular weight of gas

Actual blow-off area of test valve(mm )

: Compression coefficient according to the requirement of 4.2.2 of KS

for air, = 1

Absolute temperature of gas (K)

B 6352,

: Factor depending on vapor property according to the requirement of 4.2.2 of

KS B 6352

(i) Determination of blow-off coefficient ( ′ ) by measurement of actual blow-off rate

′

where,

: Actual blow-off rate (kg/h)

: Theoretical blow-off rate (kg/h)

(ii) Determination of nominal blow-off coefficient ( )

When blow-off coefficient obtained from (i) above satisfy the requirement of (5)

(A) (d) above, the arithmetic mean value is to be the nominal blow-off coefficient of each safety valve.

100 Guidance for Approval of Manufacturing Process and Type Approval, Etc. 2015

where,

: Number of trial

(6) Calculation of nominal blow-off rate

(A) Calculation of nominal blow-off rate ( )

(B) Conversion of blow-off rate of gas having known property

The conversion may be in accordance with the following when applying pressure than measured pressure.

(a) Case of conversion from value for steam

is not less

(b) Case of conversion from value for air or gas having known property

′

where,

: Actual blow-off rate (kg/h)

: Absolute pressure of fluid at valve inlet (MPa)

: Gas

: Steam

1 : Air or gas having known property measured blow-off rate 2 : Gas having known property in order to convert blow-off rate

Guidance for Approval of Manufacturing Process and Type Approval, Etc. 2015 101

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