What is a hydrostatic pressure test

Pressure tests

According to Annex I of the Pressure Equipment Directive, the acceptance of the pressure equipment during production must include a pressure resistance test, which is normally carried out in the form of a hydrostatic pressure test. In the case of pressure vessels, the hydrostatic test pressure - if applicable - must correspond to the higher of the following values:

  • 1.25 times the maximum load on the pressure equipment in operation, taking into account the maximum permissible pressure and the maximum permissible temperature, or
  • 1.43 times the maximum allowable pressure.

This test can be carried out on a statistical basis for series-produced pressure equipment of category I.

If the hydrostatic pressure test is disadvantageous or cannot be carried out, other tests that have proven to be effective can be carried out. For tests other than the hydrostatic pressure test, additional measures such as non-destructive tests or other equivalent methods must be applied beforehand.

Gas pressure tests and the associated test pressure factors are not directly mentioned in the Pressure Equipment Directive. However, the possibility of a gas pressure test is also opened up in the manufacturing process of pressure equipment according to PED, since other test methods than the hydrostatic pressure test can be used if this proves to be disadvantageous or inapplicable.

In general, the manufacturer can deviate from the specifications of the test pressure factors according to Section 7.4 in Annex I of the PED if the test method used is equivalent to the method described there. It must be proven that the overall safety to be demanded and verified by testing is also achieved with the selected method. If lower test pressures are used - for example in the case of a gas pressure test with the previously used test pressure factor of 1.1 - the equivalent safety of the products must be proven with additional measures.

These additional measures concern both the design and manufacture of the relevant pressure equipment and test measures that go beyond the pure gas pressure test. The use of a gas pressure test with a test pressure that is reduced compared to the hydrostatic pressure test according to Section 3.2.2 in Annex I of the PED when the pressure equipment is accepted must have been taken into account in the design, construction and production phase.

In the course of the production of simple pressure vessels in accordance with Directive 87/404 / EEC, a water pressure test or an air pressure test with an equivalent effect is used with a pressure Ph that corresponds to 1.5 times the design pressure in order to check their density. In order to carry out air pressure tests, the Member State in which the test takes place must have approved the safety procedures for the test.

The Ordinance on Industrial Safety and Health must be observed as a regulation for the assembly, installation and operation of pressure vessels or pressure vessel systems. According to this, recurring tests must be carried out for parts of the system of steam boiler systems, pressure vessel systems, systems for filling compressed, liquefied or pressurized gases and pipelines, which also include strength tests. The recurring strength tests for pressure equipment and simple pressure vessels must be carried out every ten years at the latest.

The term strength test is not specified in the Industrial Safety Ordinance. The corresponding more specific technical rule of the Committee for Industrial Safety has not yet been published. Since the previous technical rules for pressure vessels, pipelines, steam boilers and other systems requiring monitoring with regard to the operational requirements continue to apply until the revision by the Committee for Industrial Safety and their notification by the Federal Ministry of Labor and Social Affairs, the recurring pressure tests can also continue as strength tests on this basis be performed. First of all, this means that the stipulations made there about the level of the test pressure to be used still apply (at least 1.3 times the maximum permissible pressure for liquid pressure tests (figure) or 1.1 times the maximum permissible pressure for gas pressure tests; higher test pressures are required in justified individual cases permissible).

Fluid pressure tests:

The test requirements include to consider:

  • A fluid pressure test is usually carried out with water, provided that the design or operating mode of the pressure vessel / pipeline or the material to be coated allow this. Other suitable, non-hot liquids, e.g. B. petroleum, other mineral oil products, especially hydraulic oil, if appropriate.
  • The test is to be carried out at ambient temperature. At ambient temperatures of £ 0 ° C, a water pressure test may only be carried out if it is ensured that the test medium, the pressure gauge and the supply lines cannot freeze.
  • When determining the test pressure, additional loads, e.g. B. due to an increased differential pressure in outer shells with negative pressure or the additional static pressure of the test liquid column in relation to the operating medium (with its density and maximum level) can be taken into account.
  • The decrease in the strength values ​​of the materials and material compounds used with increasing temperature must be taken into account in the pressure test concept in the course of the manufacturing process of pressure equipment according to PED. If the test temperature (usually room temperature) is below the maximum permissible temperature (for which the pressure device is designed), the test pressure must be corrected with the test pressure factor 1.25 in the ratio of the strength parameters at test temperature or design temperature and this value as test pressure factor in to be used during the test if this correction leads to a test pressure factor above 1.43.

With regard to the process, the following should be observed:

  • The pressure chamber must be vented in such a way that it is completely filled with test liquid.
  • During the liquid pressure test, the outer walls and detachable and non-detachable connections of the test object must be dry. As a rule, leaks cannot be determined from the pressure gauge display.
  • The test object should be pushed forward step by step up to the permissible operating pressure. Only then should the pressure be slowly increased to the specified test pressure and then held for a long enough time, usually half an hour. Then the test pressure must be slowly reduced to the permissible operating pressure.

Gas pressure tests:

When performing gas pressure tests, the following general requirements must be taken into account:

  • Before the gas pressure test, internal, non-destructive or other tests and, if necessary, external tests must be carried out on pressure vessels. These tests, including their evaluation, must be completed before the gas pressure test. The gas pressure test with its increased risk potential can only be carried out if the results of all tests to be carried out beforehand do not show any safety-related objections.
  • The systems or system parts pressurized with gas must be made of a tough material. This also applies accordingly to components made of plastic.
  • As a rule, a gas pressure test may only be carried out if the weld seams in metallic materials have been tested non-destructively in relation to the object.

The requirements for the course of the examination include in particular:

  • The pressure is expediently increased in stages up to the test pressure and, at the stop point in the range from 0.2 to 0.5 bar, a leak test is carried out on the pressure vessel or pipeline to be tested. For this purpose, the pressure-bearing parts are moistened with foam-forming liquid at points that require special attention (e.g. weld seams, seals or fittings). At the other stopping points (the maximum permissible pressure is half or fully reached), the pressure vessels or pipelines are usually checked by visual and noise control.
  • If the result is positive, the pressure is increased further. The test pressure must be maintained for a long enough time, usually half an hour. Changes in pressure due to temperature equalization must be taken into account. As long as the pressure is greater than the permissible operating pressure, the locked area must not be entered.
  • After the test pressure has been reduced to the permissible operating pressure, the tightness is checked again. This is usually done by visual and noise control or by testing with a foam-forming agent.

Special personal protection measures must be taken during gas pressure tests. These include:

  • The area around the pressurized gas pressure vessel or pipelines, the z. B. is not shielded by other system parts, buildings, walls, depending on the local conditions, must be blocked off in a clearly visible manner. This area may only be entered by the persons entrusted with the test and when the pressure is below the permissible operating pressure. Required operating elements are to be attached at a safe distance.
  • The time of the test should be chosen so that as few people as possible are in the immediate vicinity of the cordoned off area.
  • Measures must be specified so that no hazards (e.g. due to the displacement of atmospheric oxygen) can occur when the test gas is blown off or released.

literature

  • Law on technical work equipment and consumer products (Equipment and Product Safety Act - GPSG) (CHV 3)
  • 14th Ordinance on the Equipment and Product Safety Act (Pressure Equipment Ordinance - 14th GPSGV)
  • Ordinance on safety and health protection in the provision of work equipment and its use at work, on safety in the operation of systems requiring monitoring and on the organization of occupational health and safety (Industrial Safety Ordinance - BetrSichV) (CHV 16)
  • Directive 2001/95 / EC of the European Parliament and of the Council of December 3, 2001 on general product safety
  • Directive 97/23 / EC of the European Parliament and of the Council of 29 May 1997 on the approximation of the laws of the member states relating to pressure equipment
  • Technical rules for operational safety on the Internet
  • TRB-TB Technical Rules for the Pressure Vessel Ordinance - Pressure Vessels (TRB), Pipelines (TRR) (paperback edition)
  • Printing devices online
  • Pressure Equipment Directive (PED): Overview - Online information from the European Commission
  • European Agency for Safety and Health at Work (information from the European Agency)

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