Regulations

Salient Features of Indian Boiler Regulations, 1950

Indian Boiler Regulations, 1950 is a voluminous work of specifications for design, fabrication, testing and certification of boilers and boiler components manufactured and erected in India. It is periodically updated by Central Boilers Board, New Delhi.

1. DESIGN – Working Pressure Equation: Most of the boiler components like drum, header, pipe and tube are cylindrical in shape. Internationally Boiler Codes use some variation of thin-wall formula of pipe, called the membrane formula, as the design equation for the determination of maximum allowable working pressure, P of such parts: P = 2tS/d where S is maximum allowable stress for the material of pipe, d is ID of pipe and t is thickness of pipe. This gives a liberal value for P. Barlow’s equation uses D, the OD of pipe instead of d: P = 2tS/D. This gives a conservative value for P. IBR uses the average diameter (D - t) so that the equation becomes P = 2tS/(D – t). This gives a fair value of P for a wide range of D/t ratio in use in boiler industry.

2. DESIGN – Allowable Stress Formula: IBR assumes the creep range to start from 850 deg F (454 deg C). In the non-creep range minimum of UTS/2.7 and Yt/1.5 is taken as the allowable stress, where Yt is the yield strength of material at design temperature. In the creep range minimum of Yt/1.5 and Sr/1.5 and Sc is taken as the allowable stress, where Sr is the creep rupture strength and Sc is the creep strength of material. Generally this formula gives liberal values of allowable stress as compared to ASME Boiler Code. However, this formula cannot be used for materials conforming to ASME specification, in which case IBR forces the designer to use the corresponding values of allowable stress given in ASME Code.

3. FABRICATION – Materials: Specifications for popular carbon steels, Cr-Mo alloy steels and Cr-Ni austenitic stainless steels in various product forms like plates, pipes, tubes, forgings and castings are given in IBR in chapter 2. However, fabricators generally prefer materials conforming to ASME and ASTM specifications – popular among them are SA515 Gr70, SA516 Gr70 and SA299 carbon steel plates, SA106 GrB, SA106 GrC carbon steel pipes, SA335 P11, SA335 P22, SA335 P91 alloy steel pipes, SA210 GrA1, SA210 GrC carbon steel tubes, SA213 T11, SA213 T22, SA213 T91 alloy steel tubes, SA213 TP347H stainless steel tubes, SA105 carbon steel rods, SA182 F22 alloy steel rods, SA234 GrWPB, SA234 GrWPC carbon steel fittings, SA234 GrWP11, SA234 GrWP22 alloy steel fittings, SA216 WCB carbon steel castings, and SA217 WC6, SA217 WC9 alloy steel castings.

4. FABRICATION – Welding: Welding is the major fabrication process employed in the boiler industry. IBR stipulates that only qualified welders can be engaged in welding pressure part joints – it specifies detailed procedure, in chapter 13 for qualifying welders in plate and pipe & tube in various positions. Stress Relieving is the major heat treatment process employed in the boiler industry. IBR specifies a range of 20 degrees either side of 600 deg C for soaking temperature for carbon steels. For alloy steels ASME Boiler Code and ANSI Power piping Code are generally referred by the boiler manufacturers. IBR specifies 2.5 minutes per mm of thickness for soaking time.

5. FABRICATION – Testing: IBR stipulates Radiography Testing or Ultrasonic Testing for critical butt joints of pressure parts like weld seams of drums of water-tube boilers and shells of shell-type boilers. For procedure and acceptance criteria of these non-destructive tests international codes like ASME Boiler Code are referred by the boiler manufacturers. For drum seams of water-tube boilers and shell seams of shell-type boilers, IBR also requires test plates which are to be destructively tested - procedure and acceptance criteria are vividly described in chapter 5 and chapter 12 respectively. IBR requires hydraulic testing of shell-type boilers and critical boiler components of water-tube boilers like drums to 1.5 times their maximum allowable working pressures.

6. CERTIFICATION: For the purpose of certification IBR has given various forms for various boiler components – important forms are listed below:

Form II – Certificate of Inspection during Construction

Form III – Constructor’s Certificate of Manufacture and Test

Form IV – Steel Maker’s Certificate of Manufacture and Results of Tests

Form XIII – Qualified Boiler Welder’s Certificate