UG99-e

The test pressure formula:

P_t = 1.3 MAWP x (S_t /S_d)

P_t = Test Pressure

S_t = Allowable stress at temperature of hydrotest

S_d = Allowable stress at design temperature

Note: (S_t/S_d) will always be equal to or greater than 1!

Hydrotest Procedure – From the Code

1.    Complete all pre-hydro work & examination.

2.    Assure vessel & support structure is designed for weight of hydrotest liquid.

3.    Select hydrotest fluid - any non-hazardous liquid below its boiling point.

4.    Disconnect or "blind off" appurtenances not to be tested.

5.    Vent off high points to remove possible air-pockets.

6.    Test fluid should be 30 ºF (17 ºC) above the MDMT but not need exceed 120 ºF (48 ºC)

7.    Pressure gauges must be acceptable range.  About 2 times test pressure.  (Acceptable range is 1½  to 4 times Test Pressure)

8.    Pressure gauge should be calibrated.

9.    Pressure gauge should be connected directly to vessel.  If not visible, another should be connected near operator.  (Be sure to understand effect of static head on pressure.)

10. Check tightness of test equipment.

11. Perform pressure test at 1.3 times MAWP corrected for temperature.

12. Minimum inspection pressure:  Test Pressure divided by 1.3

A vessel is constructed of a P-1 material. The vessel is stamped MAWP – 300 psi at 800 ºF.  Material allowable stress “S” is:

            100 ºF = 20,000 Psi

            800 ºF = 13,500 Psi

 Determine the:

            a.  Hydrostatic Test Pressure

            b.  Minimum Inspection Test Pressure

1. Calculate Test Pressure

Givens:          MAWP = 300 psi,
S_t = 20,000 psi,
S_d = 13,500 psi

Formula:        P_t = 1.3 MAWP x (S_t/S_d)
P_t = 1.3 (300) x (20,000/13,500)
P_t = 390 x 1.481
P_t = 577.7 psi

Hydrotest pressure is 577.7 psi at the top of the vessel.

2. Calculate minimum Inspection Test Pressure

Formula:        P_Insp = P_t /1.3
P_Insp = 577.7 /1.3
P_Insp = 444.4 psi