Maximum Allowable Working Pressure of Carbon Steel Header Pipe – Indian Boiler Regulations (IBR) 1950
In mechanical engineering and boiler design, maximum allowable working pressure (MAWP) is a critical parameter that ensures safety, efficiency, and compliance with statutory codes. The Indian Boiler Regulations (IBR), 1950 provide clear guidelines for calculating MAWP of boiler components such as headers, stubs, and pipes.
This blog explains step‑by‑step how to calculate the MAWP of a carbon steel header pipe with stubs, using Regulation 270 of IBR 1950. The solution is based on a real examination problem (CBB Part 2, 2017–2020).
Problem Statement
A 5 m long carbon steel header contains a single row of stubs at a pitch of 450 mm.
- Header pipe size: 141.3 mm OD × 6.55 mm thickness
- Maximum negative tolerance: 12.5%
- Stub size: 63.5 mm OD × 4.5 mm thickness
- Allowable stress of header material: 1200 kg/cm²
Calculate the maximum allowable working pressure (MAWP) of the header in kg/cm² as per Indian Boiler Regulations, 1950.
Step‑by‑Step Solution
1. Given Data
- Pitch (P) = 450 mm
- Outside Diameter (OD) = 141.3 mm
- Nominal Thickness (T) = 6.55 mm
- Negative tolerance = 12.5%
- Stub OD = 63.5 mm
- Stub thickness = 4.5 mm
- Allowable stress (F) = 1200 kg/cm²
2. Effective Thickness
Considering negative tolerance:
T_min = T * (1 - 0.125) = 6.55 * 0.875 = 5.73 mm
3. Internal Diameter
ID = OD - (2 * T_min) = 141.3 - (2 * 5.73) = 129.84 mm
4. Stub Internal Diameter
ID_stub = 63.5 - (2 * 4.5) = 54.5 mm
5. Ligament Efficiency
E = (P - d)/P = (450 - 54.5)/450 = 0.87
6. Regulation 270 Formula
According to IBR Regulation 270:
Final Answer
The maximum allowable working pressure (MAWP) of the carbon steel header pipe is:
76.94 kg/cm² (as per IBR 1950 Regulation 270).
Conclusion
This calculation demonstrates how boiler design engineers apply IBR 1950 rules to ensure safety and compliance. By understanding ligament efficiency, negative tolerance, and allowable stress, engineers can confidently determine the safe working pressure of boiler components.
Such problems are frequently asked in CBB examinations and are highly relevant for professionals preparing for boiler operation engineer(BOE) certification exams or working in power plants, refineries, and industrial boiler systems.