safety valve - all regulations.docx

7/27/2019 Safety Valve - All Regulations.docx

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Reg. 290

Chests etc., in General

a) All chests and fittings shall be smooth, sound and free from flaw, cracks or other injurious

defects. After completion, the chests shall be tested hydraulically at the manufacturing worksto at least twice the working pressure of the boiler for which they are intended.

Hydraulic test shall be made with water which may contain a corrosion inhibitor, with

kerosene or which other suitable liquid provided its viscosity is not greater than that of water

at a test temperature not above 52 C.

b) Valves may be fabricated from seamless steel pipes of pressure not exceeding 250 pounds

per square inch and temperatures not exceeding 800ºF. The welding should conform to

Regulation 125 and valve chest should be stress relieved after fabrication. Valves meant for

use in pipe work may also be fabricated by welding from seamless steel pipes but no

restriction as above regarding pressure and temperature shall apply to them provided the

welding complies with all the relevant requirements of fusion welding such as stress relieving

and radio-graphic inspection of the weld and the like prescribed in Chapter V of these

Regulations.

The working pressure of the chests shall be determined by equation 91 or 91A, whichever is

applicable, where the term „2 Se‟ shall be substituted by the term „1.8 x S‟ The wall thickness

shall not be less than 3/8”. The fabricated valves with their assembled fittings shall withstand

satisfactorily a hydraulic test to the same pressure as will be applied to the drum during its

registration.

c) The working pressure and the thickness of Bronze and Cast Iron Valve chests shall be

determined by the following formulae, subject to minimum thickness as specified in

regulation 283 (b):

WP=R x ( T - C )

Eqn.(76)4.5 x D

T =4.5 x WP x D

+ C Eqn.(77)R

Where,

R is the minimum specified tensile strength of the grade of the material.D - is the external diameter of the chest.T - is the minimum thickness of the chest, excluding tolerance andC - is the minimum positive tolerance as specified here under:-For Bronze Chests C = 1.5 mm

For Cast Iron Chests C = 5 mm

http://dipp.nic.in/boiler_rules_updated/reg125.htm

http://dipp.nic.in/boiler_rules_updated/chapter5.htm







d) The working pressure and the thickness of the steel valve chest of circular cross section

shall be determined by the following formulae, namely:-

Working Pressure =2f ( T - C )

D - T+ C

T =WP x D

+ C2f + WP

f = allowable stress in kg/mm2 for the material at the working metal temperature “t” to be

determined on the basis given below:-

The allowable stress “f‟” at or below 454oC is the lower of the following two values.

f =E

or f =R

1.5 2.7

For temperatures above 454oC; the least of the following three values.

a) f =Et

1.5

b) f =SR

1.5

c) f = Sc

where,

Et = Minimum value of yield point (0.2 percent proof stress) at temperature „t‟

R = Minimum specified tensile strength for the grade of steel concerned at room

temperature.

Sr = the average stress for the grade of steel concerned to produce rupture in 100,000

hours.

If the width of the scatter band of results obtained when determining this value exceeds ±20percent of the average value, then Sr shall be taken as 1.25 times the minimum stress at

temperature, „t‟ to produce rupture in 100,000 hours..

Sc = The average stress to produce an elongation (creep) of 1% in 100,000 hours for the

grade of steel concerned at temperature „t‟. For metal temperature t below 250oC values of

„f‟ for 250oC shall be used.

Note 1:- In case Sc values are not available in Material Standard and such materials are

known to have been used in boiler in India or abroad, then for such materials, the allowable

stress may be taken as the lower of



Etor

Sr

1.5 1.5

Note 2:- The allowable stress for cast steel shall be 80 per cent of that determined on the

above basis.

D = the external diameter of the chest

C = the minimum thickness of the chest, excluding tolerance and

T = the minimum positive tolerance as specified hereunder;

For cast steel chest C=5 mm

For forged or stainless steel chest C=2.5 mm

Note: Over and above the calculated thickness, additional thickness needed for assembly

stresses, valve closing stresses, shapes other than circular and stress concentrations, shall

be provided by the manufacturers to the satisfaction of the Inspecting Authority.

e) The number of valves and fittings which shall be made available to the Inspecting Officer

(excluding mechanical tests) shall be as follows:

Upto and including 51 mm 10 percent.

Over 51 mm and upto and including 76 mm 15% of the number of chest.

Over 76 mm and upto and including 114mm 20% of the number of chest

Over 114 mm 100%

If the Inspecting Authority is satisfied that the manufacturer has adequate facilities for testingand inspection of valves intended for service pressure exceeding 10.5 kg/cm2 or

temperature exceeding 204oC and actually tests each fitting at his works, the Inspecting

Authority may, at his discretion, undertake test on a sample basis.”

f) The working pressure and the minimum thickness of the steel valve chest of spherical cross

section shall be determined by the following formula, namely:-

Working pressure =4 f ( T - C )

D - 0.8 (T - C)

T =WP x D

+ C4 f + 0.8 WP

where,

T = the minimum thickness of the chest.

D = the external diameter of the chest

f = allowable stress for the material to be determined on the basis given in clause (d) above.

C= the minimum positive tolerance as specified hereunder;

For Cast Steel Chest C=5 mm.For Forged or stainless steel chest C=2.5 mm.



Reg. 350

Steel Pipes

The maximum working pressure allowed on steel pipes shall be determined by the following

formula:

a) Where the outside diameter is the basis for calculation.

W. P. =2 f e (t - c)

Equation 91D - t + c

b) Where the inside diameter is the basis for calculation.

W. P. =

2 f e (t - c)

Equation 91Ad + t - c

Where

t = Minimum thickness

W. P. = Maximum working pressure

f = Allowable stress as provided under regulation 271

D = Outside diameter of pipe

d = Inside diameter of pipe

e = Efficiency factor

= 1.0 for seamless and for electric resistance welded steel pipes and for electric fusionwelded steel pipes complying with the requirements of Chapter II in which the weld is fully

radiographed or ultrasonically tested.

= 0.95 for electric fusion welded steel pipes complying with the requirements of Chapter II,

= 0.90 for welded steel pipes for values of t up to and including 22mm.

= 0.85 for welded steel pipes for values of t over 22mm and up to and including 29mm.

= 0.80 for welded steel pipes for values of t over 29 mm.

C = 0.75mm

Note: In case Sc values are not available in Material Standard and such materials areknown to have been used in boilers in India or abroad, then for such materials, the allowable

stress may be taken as the lower of

Etor

Sr

1.5 1.5

Carbon Steel

Seamless, hydraulic

lap welded and

The lower value obtained

on the following basis from







Electric resistance welded

for temperatures up to and including

350°C (662°F)T.S

orEt

2.7 1.5

For temperatures above 454°(850°F)Molybdenum steel seamless

Etor

Sror Sc

1.5 1.5Chromium Molybdenum Steelseamless

where, T. S. = Minimum Tensile strength at 20°C(68°F)

Et = Yield point (0.2% proff stress) at the temperature t.

Sr = The average stress to produce rupture in 100,000 hours and in no case, more than 1.33

times the lowest stress to produce rupture.

Sc = The average stress to produce an elongation of 1% (creep) in 100,000 hours.

Reg. 309

Determination of Working Pressure

1. The maximum working pressure to be allowed for steel springs of round, square or

rectangular section shall be determined from the following formulae:-

For Springs in Extension.

(a) Round section: -

W.P.=10,000 p d³

Eqn. (80)DACK

(b) Square section: -

W.P.=33,333 d³

Eqn. (81)DACK

(c) Rectangular section: -

W.P.=160,000 B² H²

Eqn. (82)DACK (3B+1.8H)

where all dimensions in inches

For Springs in Compression.- The working pressure calculated by the above equation may

be increased by 25 per cent.

K = {4 D - 1} + .615 (In case of rectangular Eqn. (83)



d section substitute B for D)

{4D

- 4}D

d d

W. P. = Working pressure in lb. per square inch (set pressure). A = Loading area of valve.

d = diameter of round or side of square steel.

B = Breadth of wire (radial to spring axis).

H = Depth of wire (parallel to spring axis).

D = Mean diameter of coil

C = Constant =L 1 + L2

Eqn.(84)L1

L1 = Initial compression or extension of the spring to give the required loading (W.P.X A).

L2 = The further compression or extension of the spring to give the lift as defined in

Regulations 292 and 304.

Examples:-

C=2 where compression or extension of spring to give the required loading is ¼ diameter of

valve.

C=1.5 where compression or extension of spring to give the required loading is ½ diameter

of valve.

C=1.25 where compression or extension of spring to give the required loading is full

diameter of valve.

Note –

(1) The above formulae are based on a maximum allowable safe stress of 5,624 kg/cm²

(80,000 lbs. per square inch) on the sections of the springs under extension and 7,030

kg/cm² (100,000 lbs. per square inch), where they are in compression.

(2) The above values of „C‟ apply only to the case of „full-lift‟ Safety Valves, where L2 is equal

to D/4. In case of “high-lift” and “ordinary-lift” Safety Vales, respective values of “C” may be

worked out by using appropriate values of L2.

1) In the case of torsion bars the maximum shear stress as calculated from the following

formula shall not exceed 55 kg./mm² (80,000 lbs per square inch):-

fs =TDC

2 J

where,

fs = Shear stress.

T = Torque at set pressure.

http://dipp.nic.in/boiler_rules_updated/reg291.htm#reg292



http://dipp.nic.in/boiler_rules_updated/reg291.htm#reg292



D = Outside diameter of the bar.

J = Polar moment of inertia of the section of the bar, and

C =

Angle of twist at full lift of valve

Angle of twist at set pressure

(as furnished by the manufacturer)

The dimensions of sleeve transmitting the torque shall be of substantial proportions for the

material used

Reg. 312

Number of Effective Coils

The number of effective or free coils in a compression or extension spring shall be

determined from the following formulae:-

(i) For Round or Square Wire: -

N =KCd4

Eqn.(85)SD³

(ii) For Rectangular Wire: -

N =66 B³ H³ K

Eqn.(86)(B² + H² ) SD²

where,

N = Number of effective coils.

K = Compression or tension in inches at set pressure.

C = 22 for round, 30 for square steel.

d = diameter or side of square steel in 16th of an inch.

S = Load on spring in lbs. at blow off pressure.

D = Mean diameter of coil in inches.B = Breadth of wire in 16 th of an inch.

H = Depth of wire in 16th of an inch.

Reg. 313, Reg. 314, Reg. 315, Reg. 316

Spacing of Coils

The space between the coils when the valve is lifted 1/4 th of its diameter, shall be not less

than 1.6 mm (1/16 inch) for full lift valves and 0.8 mm (1/32 inch) for ordinary and high lift

valves."



Reg. 314

Finishing of Ends

Compression springs shall have their ends ground flat and smooth and at right angles to the

axis of the springs over the full circumference so that when placed on end on a horizontal

plane the springs will stand perpendicular.

safety valve - all regulations.docx

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