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IS 12794 (1989): Shipbuilding - Steam traps - Guidelinesfor selection [TED 19: Marine Engineering and Safety Aids]

March 1990

IS 12794 : 1989

Indian Standard

SHIPBUILDING - STEAM TRAPS - GUIDELINES FOR SELECTION

UDC 629.12.063 : 621’186.6

0 BIS 1990

BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

Price Groop 2

Marine Engineering Sectional Committee,T ED 19

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards on 18 August 1989, after the draft finalized by the Marine Engineering Sectional Committee had been approved by the Transport Engineering Division Council.

IS 12294 : 1989

Indian Standard

SHIPBUILDING - STEAM TRAPS - GUIDELINES FOR SELECTION

1 SCOPE where W

1.1 This standard specifies guidelines for selection = weight of liquid to be heated, kg

of steam traps for various application on board C, ‘= specific heat of the liquid, k Cal/kg “C

ships. n T = temp rise of the liquid, “C L = latent heat of steam k Cal/kg

2 ASSESSMENT ‘OF CONDENSATE FLOW t = time in hours

RATES 2.5 Steam Jacketed Dryers kg condensate/h

2.1 kg condensate/h of 30 m of insulated steam main line at 21°C ambient.

= 600 ( Wi -Wf)+(Wix AT) L

Steam Pressure ( bar ) r------

50 80

0’7 3 4

4 5 7

7 6 9

20 10 15

42 15 22

Steam Main Size .-,-_-_L ------_--__

100 t5O 200 252 (mm)

’ 5 8 10 12

9 14 17 21.

11 16 ?O 25

19 28 35 44

28 41 52 64

2.2 Steam Tracing Lines where

Approximate load is 30 kg/h for each 30 III of Wi = initial weight of the material, kg/h tracerline. Wt = final weight of the material, kg/h

AT = temp rise of the material, “C 2.3 General Usage Formulae L = latent heat of steam, k Cal/kg

1 Heating Water with Steam; 2.6 Heating Air with Steam Pipe Coils and I/h of water x temp rise”C Radiation

kg condensate/h = 500 AxUxAT

2 Nearing Fuel Oil with Steam: kg condensate/h = ~~~~ L -.- --

kg condensate/h = l/h of fuel oil x temprise “C where

100 ~~~ ~~- A = area of the heating surface, ma

3 Heating Air with Steam: u = heat transfer coefficient k Cal/m2 ‘JC

mR min of air X temp rise’C ( 2 for free convection ) kg condensate/h = --._-p-- --~-

27 AT = steam temp minus the air tempera- ture “C

2.4 Heating Liquids in Steam Jacketed Kettles

WxC,x AT kq condensate/h = ~~-__-. Lxt

L - latent heat of steam k Cal/kg

NOTE - The condensate load to heat the cquip- ment must be added to the condensate load for heating the material, using same formula.

3 ASSESSMENT OF PRESSURE DIFFERENTIAL

value is assessed as indicated below:

3.1 The pressure .differ.ential is the ditference between the ‘pressure (kg/cm’ ) absolute at &he where trap inlet and that at the trap outlet.

.=sw,(T, - Tb) __-- 9P

3.2 Pressure at Trap Inlet When Draining Pipes

When steam flows through a pipeline there is a drop in pressure between the beginning and end of. the line. If this pressure drop beoomes a signihcant percentage of the initial pressure ( say 10 percent ) due .to length of pipe -1iee and steam velocity, then it is necessary to assess the value and to allow for the reduced inlet pressure for those traps near the end of the line.

P = flashing factor Ts = temp of the saturated steam being

trapped Tb = temp of the steam corresponding to the

.back .pressure at the tramp, neglecting friction, “C

W m = maximum rate of condensate ,fiow ( kg/h )

P - pressure factor ,( bcy *ig. 1 )

3.3 Pressore at Inlet to Trap or O$JRV De&e 3.42 Effect of Back Pressure on Steam Trap When ,Dralning a Steam Heat User Capacity

When the steam is allowed an unrestricted flow into the steam heat user ( that is when the equip-

The total back pressure wfll petice *he c+ity of the trap by the amount given in Table 1. This

ment is required to perform the maximum of heat transfer ) it is only necessary to cal~~k~te the drop

does not apply to inverted bucket traps since

from initial pressure due to pipe friction ( from selection is made considering both inlet as well as

source to user ). back pressure.

3.4 Pressure at

L

5 IS 20 25 30 35 a

PRESSURE Famot? I

%rr;. 1 PRYSURE FACTOR GRAFH

Table 2 shows the recommended safety factors Table 2 for the various types of steam ‘traps.

Recommended Safety Factor for Steam Traps

( CIause 4.1 1

Every intending user of steam traps, must ascef- Type of Trap Saftity FtWtor

tain @he auarall UCWXditiOnS Under Which 8 oap 1s Vapour-pressure thermostatic traps 2to4 to operate. After these conditions have been determined, however, the ‘individual character& Liquid expansion trap 2to4

tics Of the various types Of Steam trap must be considered in order to select the most suitable trap

Bimetallic traps 2t;oa

for a particular application. Float traps l-5 to 2.5

5.2 Fundamental Factors Affecting Selection

A steam trap must be suitable for the steam, condensate and installation conditions. The &am trap selection table lists the factors relating to these conditions.

5.3 Maximum Steam Pressure and Temperature

Inverted bueket traps

Thermodynamic traps

2 to 3

1.2 to 2

NOTE -The actual safety factor to be used for any particular application will depend upon accuracy of the following:

1 Estimated load

2 Estimated pressure at trap Having selected a suitable type ( or types ) of trap from the selection table the user must then ascertain from the data published by the manu- facturer(s) whether the type(s) chosen is available

3 Estimated back pressure

Any unusual or abnormal conditions must be. taken into consideration.

for the required pressure.

3

IS 12794 ‘f 1989

5.4 Steam Trap Selection General Guide - ___.________~ ~--.~~

Application .

a) Air heating coils i) Low and medium pressure

ii) High pressure

b) Hot water heaters ( Instantaneous )

c) Hot water heaters ( storage ) d) Shell and tube exchanger

i) Small - high pressure ii) Large - low and medium

pressure reboilers

e) Steam humidifiers

f) Steam -jacketed vessel i) High pressure

ii) Low pressure

g) Steam line drip traps i) O- 1 kg/cm2

ii) Above 1 kg/cm” to 8 kg/cm’ iii) Above 8 kg/cm2 to 40 kg/cm” iv) High pressure - superheat

h) Steam pipe coils ( air heating ) ,

j) Steam radiators k) Steam separators

i) O- 1 kg/cm’ .i$ ~Above 1 kg/cm2 to 8 kg/cm’ iii) Above 8 kg/cm* to 40 kg/cm’

m) Steam tracer lines

n) Storage tank coils p) Submerged heating coils

i) High pressure

ii) Low and medium pressure

q) Unit heaters

Type of Trap

Float/Inverted bucket type Float/Inverted bucket type

Float/Inverted bucket type

Float/Inverted bucket type

Vapour pressure/‘Thermostatic

Float/Inverted bucket type

Float/Inverted bucket type

Thermodynamic/Float Float/Inverted bucket type

Float/Inverted bucket Thermodynamic/Float Thermodynamic Thermodynamic/Bimetallic

Vapour pressure/Thermostatic

Vapour pressure/Thermostatic

Float Thermodynamic/FIoat Thermodynamic/Inverted bucket Vapour pressure/Thermostatic/Thermodynamic/ Bimetallic Float/Inverted bucket

Thermodynamic/Vapour pressure/Thermostatic FIoat/Vapour pressure/Thermostatic Float/Vapour pressure/Thermostatic

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Amend No. Date of Issue Text Affected

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