Hydrotest

PV Elite

App. 27-4 - ASME Appendix 27-4, Division 1. The hydrotest pressure is 1.3 times the

maximum allowable working pressure for the vessel multiplied by the lowest ratio of the

stress value S for the test temperature to the stress value S for the design temperature.

This type of hydrotest is normally used for glass-lined vessels.

For Division 2, the software provides the following methods to determine hydrotest pressure.

Select one of the following:

 AT-300 - ASME AT-300, Division 2, based on vessel design pressure. The hydrotest

pressure is 1.25 times the design pressure marked on the vessel, multiplied by the

lowest ratio of the stress intensity value Sm for the test temperature to the stress

intensity value Sm for the design temperature. This type of hydrotest is normally used

for non-carbon steel vessels for which the allowable stress changes with temperature

starting even at a somewhat low temperature.

 AT-301 - ASME AT-301, Division 2, based on calculated pressure. A hydrostatic test

based on a calculated pressure is allowed by agreement between the user and the

manufacturer. The hydrostatic test pressure at the top of the vessel is the minimum of

the test pressures calculated by multiplying the basis for calculated test pressure for

each element by 1.25 and then reducing this value by the hydrostatic head on that

element.

 AT-410 - ASME AT-410, Division 2, based on vessel design pressure. The pneumatic

test pressure shall be no less than 1.15 times the design pressure multiplied by the

lowest ratio of the stress value S for the test temperature to the stress value S for the

design temperature.

Hyd. Allowable is 90% Yield

Select to use 90 percent of the ambient yield stress as the hydrotest allowable stress. Clear

to use the ASME Division 1 value, which is 1.3 times the ambient allowable stress Sa for the

material. When the vessel is tested, the largest circumferential stress should not exceed this

value. The software recalculates the hydrotest allowable each time this option is selected or

cleared.

According to ASME Section VIII Division 2, the stress limits for hydrotest pressure are in the following:

4.1.6.2 Test Condition – The allowable stress for the test condition shall be established by the following requirements. Controls shall be provided to ensure that the Test Pressure is limited such that these allowable stresses are not exceeded. When applicable, the static head and any additional pressure loadings shall be included.

a) Hydrostatically Tested Vessels – when a hydrostatic test is performed in accordance with Part 8, the hydrostatic test pressure of a completed vessel shall not exceed that value which results in the following equivalent stress limits:

1) A calculated Pm shall not exceed the applicable limit given below:

Pm <= 0.95Sy (4.1.3)

2) A calculated Pm +Pb shall not exceed the applicable limits given below:

Pm + Pv <= 1.43Sy for Pm<=0.67Sy (4.1.4)

Pm +Pb <= (2.43 - 1.5Pm) for 0.67Sy <=Pm <= 0.95Sy (4.1.5)

b) Pneumatically Tested Vessels – when a pneumatic test is performed in accordance with Part 8, the pneumatic test pressure of a completed vessel shall not exceed that value which results in the following

equivalent stress limits:

1) A calculated Pm shall not exceed the applicable limit given below:

Pm <= 0.80Sy (4.1.6)

2) A calculated Pm +Pb shall not exceed the applicable limits given below:

Pm + Pv <= 1.20Sy for Pm<=0.67Sy (4.1.7)

Pm +Pb <= (2.20 - 1.5Pm) for 0.67Sy <=Pm <= 0.8Sy (4.1.8)

Criteria for Limiting Hydrotest Stress in COMPRESS

Because ASME VIII-1 does not provide guidelines for determining allowable stress values for the test condition, COMPRESS uses the following method by default. It is taken from the 2004 Edition of ASME VIII-2, paragraph AD-151.1. If needed, you can define a different percentage of yield allowed at test in the Set Mode Options > Defaults > Testing area.

(a) P_m ≤ 0.9 * S_y

(b) P_m + P_b ≤ 1.35 * S_y for P_m ≤ 2 / 3 * S_y

(c) P_m + P_b ≤ 2.2 * S_y − 1.5 * P_m for 2 / 3 * S_y < P_m ≤ 0.8 * S_y

In the equations above, P_m is the primary membrane stress and P_b is the primary bending stress. The yield stress S_y is taken as the smallest of the shell, reinforcing pad or nozzle neck S_y values.

The discontinuity stress state at a nozzle includes both primary membrane and bending components. As equation (a) governs for shells and either equation (b) or (c) governs for nozzles, the test allowable may be different for nozzles and shells even when they are made from the same material.