Flattening of tubing in bends should not exceed what percentage of the original diameter?

• A. 20 percent
• B. 25 percent
• C. 30 percent
• D. 40 percent

Answer: (B)

When tubing is bent, the cross-section tends to flatten and the wall thickness can decrease at the bend. To keep the bend strong and ensure adequate flow, there’s a safe limit on how much the diameter can be reduced. The maximum recommended reduction is about 25 percent of the tube’s original diameter. Going beyond that means the bend could become too weak or flow could be restricted, increasing the risk of failure. A 20 percent reduction is within the limit, but it’s not the maximum; 30 percent or 40 percent would exceed the safe limit.