Wis. Admin. Code Department of Safety and Professional Services SPS 341.33

Current through October 28, 2024

Section SPS 341.33 - Protection of vessels supplied through pressure-reducing stations

(1) SIZING SAFETY VALVES. The requirements in this section shall be used for determining the sizes of safety valves on pressure vessels such as pressure cookers, indirect hot water heaters and equipment in heating systems, that are supplied through pressure-reducing stations from boilers carrying a higher steam pressure. Where a pressure-reducing station is supplied from a boiler, the capacity of the safety valves on the low-pressure side of the system need not exceed the capacity of the boiler.

(2) REDUCING-STATION CAPACITY.

(a) The following formula shall be used to determine the steam flow rate through the pressure-reducing station.

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(b) The critical flow capacity data supplied by the reducing valve manufacturer may be used in place of the above formula to select the required safety valve capacity. The capacity calculations shall be the largest obtainable by internal trim change of the reducing valve.

(c) In using Table 341.33-1, the pressure-reducing station inlet pressure is the lowest set pressure of any safety valve on the high pressure side of the pressure-reducing station.

(3) BYPASS CAPACITY. The following formula shall be used to determine the steam flow rate through the bypass when pressure-reducing stations are arranged with a valved bypass that also acts as a potential steam source hazard in case the bypass is left open.

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(4) SELECTING SAFETY VALVE. The larger of the steam flow rates calculated by the formulas in subs. (2) and (3) shall be used for selecting the safety valve on the low-pressure side of the system.

OUTLET	PRESSURE-REDUCING VALVE INLET PRESSURE, PSIG
PRESSURE PSIG
PRESSURE PSIG	1500	1450	1400	1350	1300	1250	1200	1150	1100	1050	1000	950
1000	76560	72970	69170	64950	60540	55570	49930	43930	35230	25500	-	-
950	77430	74180	70760	67000	63100	58770	53920	48610	42380	34890	24910	-
900	77750	74810	71720	68340	64870	61040	56820	52260	47050	41050	33490	23960
850	77830	74950	72160	69130	66020	62610	58900	54930	50480	45470	39660	29080
800	-	75070	72330	69490	66700	63680	60390	56910	53060	48800	43980	38340
750	-	-	--	69610	66880	64270	61260	58200	54840	51170	47080	42420
700	-	-	--	-	66900	64270	61520	58820	55870	52670	49170	45230
650	-	-	--	-	-	-	61550	58860	56260	53480	50440	47070
600	-	-	--	-	-	-	-	58980	56270	53660	51020	48470
550	53810	51040	48470
500
450
400
350
300
250
200
175
150
125
110
100
85
75
60
50
40
30
25
15
10
5

Where capacities are not shown for inlet and outlet conditions, use the highest capacity shown under the applicable inlet pressure column.

OUTLET	PRESSURE-REDUCING VALVE INLET PRESSURE, PSIG
PRESSURE PSIG
PRESSURE PSIG	900	850	800	750	700	650	600	550	500	450	400	350	300
1000
950
900
850	23190
800	31610	22550
750	37110	30600	21800
700	40860	35730	29420	21020
650	43400	39200	34250	28260	20190
600	45010	41500	37470	32800	27090	19480
550	45800	42840	39850	35730	31310	25940	18620
500	45850	43330	40530	37610	33880	29760	24630	17720
450	45870	43330	40730	38150	35260	31980	28080	23290	16680	-	-	-	-
400	-	-	40760	38220	35680	33050	29980	26380	21870	15760	-	-	-
350	33120	30690	27910	24570	20460	14790	-	-
300	33240	-	28140	25610	22620	18860	13630	-
250	28150	25650	23200	21000	17100	10800
200	21350	18250	15350
175	18250	16000
150	18250	16200
125	18780	-
110
100
85
75
60
50
40
30
25
15
10
5

Where capacities are not shown for inlet and outlet conditions, use the highest capacity shown under the applicable inlet pressure column.

OUTLET	PRESSURE-REDUCING VALVE INLET PRESSURE, PSIG
PRESSURE PSIG	250	200	175	150	125	100	85	75	60	50	40	30	25
1000
950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
200	10900
175	12600	7250
150	13400	9540	6750
125	13600	10800	8780	6220
110	13600	11000	9460	7420	4550
100	13600	11000	9760	7970	5630
85	13600	11000	-	8480	6640	4070
75	13600	11000	-	-	7050	4980	3150
60	13630	11000	-	-	7200	5750	4540	3520
50	-	11000	-	-	-	5920	5000	4230	2680	-	-	-	-
40	-	11000	-	-	-	-	5140	4630	3480	2470	-	-	-
30	-	11050	3860	3140	2210	-	-
25	3340	2580	1485	-
15	2830	2320	1800
10	2060
5

Where capacities are not shown for inlet and outlet conditions, use the highest capacity shown under the applicable inlet pressure column.

Nominal pipe size, inches	STANDARD WEIGHT PIPE
Nominal pipe size, inches	Actual External Diameter, Inches	Approx. Internal Diameter, Inches	Approx. Internal Area, Square Inches
3/8............	0.675	0.49	0.19
1/2............	0.840	0.62	0.30
3/4............	1.050	0.82	0.53
1 ...............	1.315	1.05	0.86
1-1/4 ...........	1.660	1.38	1.50
1-1/2 ...........	1.900	1.61	2.04
2...............	2.375	2.07	3.36
2-1/2 ...........	2.875	2.47	4.78
3...............	3.5	3.07	7.39
3-1/2 ...........	4.0	3.55	9.89
4...............	4.5	4.03	12.73
5...............	5.563	5.05	19.99
6...............	6.625	6.07	28.89
8...............	8.625	8.07	51.15
10..............	1.750	10.19	81.55
12..............	12.750	12.09	114.80

Wis. Admin. Code Department of Safety and Professional Services SPS 341.33

Cr. Register, February, 1988, No. 386, eff. 3-1-88; am. intro., (1)(intro.), (2), r. and recr. (1) (a) and (b), Register, May, 1994, No. 461, eff.6-1-94; am. (1) (a), Register, June, 1996, No. 486, eff. 7-1-96; correction in (1) (intro.), (b), (2) made under s. 13.92(4) (b) 7, Stats., Register December 2011 No. 672; CR 11-047: (intro.), (1) (intro.) to (c), (2), (3) renum. to be (1), (2) (intro.) to (b), (3), (4) Register May 2012 No. 677, eff. 6-1-12.

In applying Table 341.33-2, the area of the pipe is always based upon standard weight pipe and the inlet size of the pressure-reducing valve.