Question
Explain the Nozzle Neck Thickness calculations as per ASME Section VIII Div.1 UG-45.
Answer
To understand nozzle neck thickness requirements, refer to ASME BPVC Section VIII, Division 1, UG-45. This section specifies the minimum wall thickness for nozzle necks and related components.
UG-45 Overview:
Definitions
- ta: Minimum neck thickness required for internal and external pressure using UG-27 and UG-28 (plus corrosion and threading allowance), as applicable.
- External forces and moments from supplemental loads (UG-22) must be considered. Shear stresses caused by UG-22 loadings shall not exceed 70% of the allowable tensile stress for the nozzle material.
- tb1: For vessels under internal pressure, the thickness (plus corrosion allowance) required for pressure (assuming E = 1.0) for the shell or head at the location where the nozzle neck attaches.
- Use the parent component radius (shell/head) in the UG-27 formula instead of the nozzle radius.
- Must not be less than the minimum thickness specified in UG-16(b).
- Use vessel corrosion allowance (Cav) instead of nozzle corrosion allowance (Can).
- tb2: For vessels under external pressure, the thickness (plus corrosion allowance) obtained by using the external design pressure as an equivalent internal design pressure (assuming E = 1.0) for the shell or head at the nozzle location.
- Must not be less than the minimum thickness specified in UG-16(b).
- tb3: Thickness given in Table UG-45 plus corrosion allowance.
- tUG-45: Minimum wall thickness of nozzle necks.
Example:
Steps:
- Calculate ta using UG-27 for internal pressure, considering nozzle material and corrosion allowance.
- Calculate tb1 using shell/head radius and assuming E = 1.0.
- Use vessel corrosion allowance (Cav) instead of nozzle corrosion allowance (Can).
- Compare ta, tb1, tb2, and tb3 as per UG-45 rules.
- Final nozzle neck thickness = max(ta, tb).
See Also