8/12/2019 ART_T_3

1/2

ARTICLE T-3

HYDROSTATIC TESTS

AT-300 HYDROSTATIC TESTS BASED ON

VESSEL DESIGN PRESSURE

Except as otherwise permitted in AT-330 and AT-

400, completed vessels designed for internal pressure

shall be subjected to a hydrostatic test pressure which,

at every point in the vessel, is not less than 1.25 times

the design pressure (see AD-121.1) to be marked on

the vessel, multiplied by the lowest ratio (for thematerials of which the vessel is constructed) of the

stress intensity value Sm for the test temperature of the

vessel to the stress intensity value Sm for the design

temperature (see Table AD-150.1).

AT-301 Hydrostatic Tests Based on Calculated

Pressure

A hydrostatic test based on a calculated pressure

may be used by agreement between the user and the

Manufacturer. The hydrostatic test pressure at the top

of the vessel shall be the minimum of the test pressure

calculated by multiplying the basis for calculated testpressure for each pressure element by 114 and reducing

this value by the hydrostatic head on that element. The

basis for this calculated test pressure is the highest

permissible internal pressure, as determined by the

design formulas, for each element of the vessel using

nominal thicknesses, including corrosion allowance, and

the allowable stress intensity values given in Subpart

1 of Section II, Part D for the temperature of the test.

When this pressure is used, it shall be as set forth in

the Design Report.

AT-302 Upper Limit of Hydrostatic TestPressure

The requirements of AT-300 represent the minimum

standard hydrostatic test pressure required by this Divi-

sion, except as permitted in AT-330. The requirements

of AT-301 represent a special test condition based on

calculations. Any intermediate value of pressure may

be used. The upper limits of hydrostatic test pressure

are established in AD-151 and AD-151.1. If the hydro-

260

static test pressure is allowed to exceed, either intention-

ally or accidentally, the value determined as prescribed

in AT-301 to the degree that the vessel is subject to

visual permanent distortion, the Inspector shall reserve

the right to reject the vessel. (See AT-330.)

AT-310 HYDROSTATIC TESTS OFCOMBINATION UNITS

Combination units shall be tested by one of the

following methods.

AT-310.1 Pressure Chambers Designed to Operate

Independently.Pressure chambers of combination units

that have been designed to operate independently shall

be hydrostatically tested as separate vessels; that is,

each chamber shall be tested without pressure in the

adjacent chamber.

AT-310.2 Common Elements Designed for a Maxi-

mum Differential Pressure. When pressure chambersof combination units have their common elements de-

signed for the maximum differential pressure that can

possibly occur during startup, operation, and shutdown,

and the differential pressure is less than the higher

pressure in the adjacent chambers, the common elements

shall be subjected to a hydrostatic test pressure of at

least 114 times the differential pressure to be marked

on the unit, corrected for temperature as in AM-300.

AT-310.3 Adjacent Chambers. Following the test

of the common elements, as required by AT-310.2,

and their inspection, the adjacent chambers shall be

hydrostatically tested simultaneously (see AT-300 andAT-301). Care must be taken to limit the differential

pressure between the chambers to the pressure used

when testing the common elements.

AT-310.4 Special Stamping and Data Report Re-

quirements for Combination Units. The vessel stamp-

ing and the Manufacturers Data Report must describe

the common elements and their limiting differential

pressure (see AS-101, AS-300, and AS-301).

merican Society of Mechanical EngineersYRIGHT American Society of Mechanical Engineersensed by Information Handling Services

8/12/2019 ART_T_3

2/2

AT-320 PART AT TESTING AT-355

AT-320 VESSELS DESIGNED FOR

VACUUM

Vessels designed for a vacuum or partial vacuum

only and chambers of multichamber vessels designed

for a vacuum or partial vacuum only shall be subjected

to an internal hydrostatic test or, when a hydrostatictest is not practicable, to a pneumatic test in accordance

with the provisions of Article T-4. Either type of test

shall be made at a pressure not less than 114 times

the difference between normal atmospheric pressure

and the minimum design internal absolute pressure.

AT-330 ENAMELED VESSELS

The test pressure for enameled vessels shall be at

least equal to but need not exceed the design pressure

to be marked on the vessel.

AT-340 PAINTED/COATED/LINED VESSELS

Vessels, except for those in lethal service as defined

in AG-301(c), may be painted or otherwise coated

either internally or externally, and may be lined inter-

nally, prior to the pressure test. However, the user is

cautioned that such painting/coating/lining may mask

leaks that would otherwise have been detected during

the pressure test.

AT-350 HYDROSTATIC TESTING

PROCEDURE

AT-351 Provision of Vents at High Points

Vents shall be provided at all high points of the

vessel in the position in which it is to be tested to purge

possible air pockets while the vessel is being filled.

261

AT-352 Fluid Media and Temperatures for

Hydrostatic Tests

Any liquid, nonhazardous at any temperature, may

be used for the hydrostatic test if below its boiling

point. Combustible liquids having a flash point less

than 110F (43C), such as petroleum distillates, maybe used only for near atmospheric temperature tests.

It is recommended that the metal temperature during

hydrostatic test be maintained at least 30F (17C)

above the minimum design metal temperature, but need

not exceed 120F (49C), to minimize the risk of brittle

fracture. The test pressure shall not be applied until

the vessel and the pressurizing medium are at about

the same temperature. If the test temperature exceeds

120F (49C), it is recommended that examination of

the vessel required by AT-355 be delayed until the

temperature is reduced to 120F (49C).

AT-353 Check of Test Equipment Before

Applying Pressure

Before applying pressure, the test equipment shall

be inspected to see that it is tight and that all low-

pressure filling lines and other appurtenances that should

not be subjected to the test pressure have been discon-

nected or isolated by valves or other suitable means.

AT-355 Examination for Leakage After

Application of Pressure

Following the application of the hydrostatic test

pressure, examination for leakage shall be made of alljoints and connections and of all regions of high stress

such as head knuckles, regions around openings, and

thickness transition sections. This examination shall be

made at a pressure equal to the greater of the design

pressure or three-fourths of the test pressure and shall

be witnessed by the Inspector. Any leaks that are

present shall be corrected in accordance with the rules,

after which the vessel shall be retested in accordance

with these requirements.

merican Society of Mechanical EngineersYRIGHT American Society of Mechanical Engineersensed by Information Handling Services