Tube Rupture Case

Tube rupture may be occurred for shell and tube heat exchanger type. Based on my experience, some design philosophy using 2/3 rule, and some other using 10/13 rule for the criteria of requirement PSV for tube rupture. Which one is correct? Should we apply 2/3 or 10/13 rule?

Tube rupture is possible cause overpressure in shell and tube heat exchanger type if Test Pressure of Low Pressure Side LESS than design pressure of High Pressure Side. That is where 2/3 and 10/13 rule coming from. For equipment with test pressure = 1, 5 x design pressure, the 2/3 (=10/15) rule is applied, whereas for test pressure = 1, 3 x design pressure, the 10/13 rule is applied

When tube ruptures, fluid will flow from high pressure side to low pressure side. Check whether increasing pressure at low pressure side due to tube rupture possible exceeds the corrected test pressure or not. If YES, the tube rupture case applicable to be considered

My friend, do you know, why API STD 521 use term corrected test pressure to evaluate the possibility of overpressure due to tube rupture? hydrotest pressure is conducted at ambient temperature, therefore the correction is required because tube rupture is not occurred at ambient temperature.

The corrected test pressure can be calculated with this following formula.

Allowance stress at ambient temperature > allowance stress at elevated temperature, therefore from above formula, corrected hydrotest pressure > uncorrected hydrotest pressure. In other word, we can use uncorrected hydrotest pressure for checking whether tube rupture is applicable to be considered or not. This understanding is very useful, especially when we don’t have the data of allowance stress.

Hopefully this picture gives a simple explanation.

Thank for reading, hopefully this posting useful for you

Have a great day…