Tag: Stress

Stress Analysis

• Permissible load variation is determined as the ratio of (Travel x Spring rate / Load ) based on max. operating condition.
• Cold Load = Hot Load + Movement x Spring Rate (For pipe movement up)
• Cold Load = Hot Load – Movement x Spring Rate (For pipe movement down)
• the load variability shall be up to 25% throughout the total travel. However, for critical systems such as piping connected to pumps, compressors, reboilers, etc. lesser load variation is required to meet the allowable load requirements.
• if the load variation exceeds the allowed value, in the same load range selects a spring with lower spring rate. Else, select higher size spring.

Data required for flexibility calculations
1. Code of Practice
2. Basic Material of Construction of Pipe
3. Ambient / Installation temperature
4. Number of Thermal Cases
5. Flexibility Temperature (See Note)
6. Design Pressure
7. Outside diameter of Pipe
8. Type of construction of pipe
9. Nominal Thickness of Pipe
10. Manufacturing tolerance
11. Corrosion allowance
12. Pipe Weight
13. Insulation Weight
14. Specific Gravity of Contents
15. Young’s Modulus at Ambient/Installation Temperature
16. Young’s Modulus at Flexibility Temperature
17. Thermal Expansion at Flexibility Temperature
18. Allowable stress at Ambient/ Installation temperature
19. Allowable stress at flexibility temperature
20. Bend radius and type of bend
21. Branch connection type
22. Weight of attachments – Valves and Specialties
23. Terminal movements with directions

A maximum variability factor of 25% has been established by MSS to limit the load differential which may be prescribed in a variable spring support

Travel stops are installed in all constant spring support before shipping. These must be present during any hydro testing, but must be removed during installation before normal operations

Design pressure safe for short occasional or short operating periods if higher than design pressure if loop pressure less than (Y SA max allowable pressure)
Y = 15% if event less than continuous 8 hrs/day or 800 hr/year
Y = 20% if event less than continuous 1 hrs/day or 80 hr/year

Maximum sustained pressure + occasional pressure + transient pressure less or equal design pressure by code