Branch Reinforcement

When there is an opening in the pipe, it may be necessary to add additional metal around the hole to compensate for the weakening effect of the opening. The reinforcement material must be sized and placed to preserve the general strain pattern predominating in the pipe and to avoid creating n overriding stress concentration itself.

The design of branch connections to sustain internal pressure in cases where the angle between axes of the branch and of the run pipe is between 45 and 90 degrees (inclusive) can be made according to code rules as follows:

Required Reinforcement Area

Available Reinforcement Area (without a pad):

Excess areas lying within the reinforcement zone resulting from any excess thickness available in the run pipe and branch pipe.

These areas are all within the reinforcement zone and are further defined below:

• Area A2 is the area resulting from excess thickness in the run pipe wall, which is basically the area available in the Pipe Header.

• Area A3 is the area resulting from excess thickness in the branch pipe wall, which is basically area available in the pipe branch.

• Area A4 is the area of other metal provided by welds and properly attached reinforcement which basically cross-sectional area of welds.

Where,

• T_h and T_b = Nominal thickness of pipe header and pipe branch respectively, inches
• t_h, t_b = Pressure design thickness of header pipe and pipe branch respectively, inches
• c = Corrosion Allowance, inches
• m = Mill Tolerances, inches
• β = Angle of Branch connection, degrees.
• d₁  = Actual corroded length removed from run pipe, inches
• d₂ = Half width of reinforcement zone, inches
• d₂ = d₁

OR:

= whichever is greater, but in any case, not more than the outside diameter of the header pipe.

• t_r = Nominal thickness of reinforcing pad, thickness
• L₄ = Height of reinforcement zone outside of run pipe, inches
•     = 2.5 ( T_h – c), or
•     = 2.5 (T_b – c) + t_r

Whichever is lesser.

Application:

• If A2 + A3 + A4 ≥ A1, then the opening is adequately reinforced.
• If A2 + A3 + A4 < A1, then it can be said that reinforcing pad is required.

Standard Pad Size:

• Thickness = Thickness of run pipe
• Width = Half the normal diameter of branch pipe