API Spec 6A and 16A require manufacturers to conduct hydrostatic body proof tests of individual units of pressure containing equipment. This simply means that all equipment units that have designs which include a “body” portion with end connectors (perhaps with outlets and bonnet attachment points) shall experience a hydrostatic pressure test to a specified “TEST PRESSURE”, for a specified hold period, for a specified number of cycles, at the time of original manufacture.
This test procedure also applies to any API Spec 6A and 16A equipment that has experienced weld repair and stress relief on the body or pressure containing components.
Passing this test requires that the equipment retain the specified pressure for the specified time (hold period) and the specified number of cycles without pressure release or visible leakage.
API Spec 6A does not require a hydrostatic pressure test for loose connectors, such as blind flanges and studded adapters. API Spec 16A does require a hydrostatic test for studded adapters and clamps.
Caution: Never confuse “Test Pressure” with “Working Pressure” (working pressure and rated pressure mean the same thing). Do not apply test pressure to any closure parts within equipment units, e.g. BOP rams, valve gates, choke needles and seats. Hydrostatic pressure applied to these closure parts should never exceed the equipment rated working pressure. Consult API specifications 6A and 16A for the specific details on the testing of closure mechanisms.
When checking for visible leakage, never look directly into equipment bores with closure mechanisms holding pressure. Never stand close to equipment under test pressure. Thoroughly dry all assembled equipment surfaces before testing, and look for evidence of leakage after pressure release. Operators should not apply these test pressures in the field; field tests should not exceed the rated working pressure of the equipment.
The following table provides a guide to test pressures for API Spec 6A equipment with specific working pressure ratings. API Spec 16A test pressures equal the pressures in this table except for those working pressures marked with a double asterisk.
API 6A Test Pressures for Equipment with Specific End and Outlet connections
|Nominal Size Flange||Casing Threads|
|Working Pressure Rating (psi)||13-5/8″ and Smaller (psi)||16-3/4″ and larger (psi)||Line Pipe and Tubing Threads (psi)||4-1/2″ to 10-3/4″ (psi)||11-3/4″ to 13-3/8″||16″ to 20″|
** API Spec 16A specifies all test pressures for all sizes of equipment as 1.5 times working pressure including smaller sizes of 2000 psi and 3000 psi working pressure equipment.
Apply test pressure two times. The first application of pressure shall continue for a minimum of 3 minutes. The second application of pressure shall also continue for 3 minutes minimum, or for API Spec 6A, PSL 3,PSL 3G and PSL 4, and API Spec 16A equipment, the second test shall continue for a minimum of 15 minutes. For acceptance, equipment shall show no visible leakage under test pressure.
For PSL 3G and PSL 4, a working pressure gas test shall follow the successful hydrostatic test. Reference the gas body test, valve seat test, and gas back-seat test in API Spec 6A for acceptance criteria.
Exception: Leakage by the thread during the hydrostatic testing of a threaded wellhead member, when joined to a threaded test fixture, shall not void the test so long as the leak initiated above the rated working pressure of the thread and allowed the maintenance of the required pressure for the required hold period. See Table 2 below for the working pressure rating for API Internal threaded end or outlet connections.
The table below provides the working pressure rating for Internal threaded end and outlet connections on API Spec 6A equipment.
Working pressure ratings for internal threaded end or outlet connections
|Type of Thread||Nominal Pipe Size (Inches)||Rated Working Pressure (psi)|
|3/4 to 2||5,000|
|2-1/2 to 6||3,000|
external upset round thread)
|1,050 to 4-1/2||5,000|
(8 round, buttress and extreme line)
|4-1/2 to 10-3/4||5,000|
|11-3/4 to 13-3/8||3,000|
|16 to 20||2,000|
Always have valves and chokes in the partially open position during body testing.
Test each bore of multiple-bore equipment individually.
Test pressure requirements assure that the body of an equipment unit, with any connection thereon, has the capacity to hold and retain fluid at the rated working pressure, with a margin of safety.
Tests of equipment closure parts equal to rated working pressure demonstrate the functional reliability of the equipment to operate and control the flow, or stop the flow, of fluids passing through the equipment at pressures equal to or less than the rated working pressure.