Pneumatic test

Based on our practical experiences in the applieation of AE on pressure equipments since 1979, we started in the year 1994 to apply AE on steam drums in combination with pneumatic tests. Before we are able to do this, we have to perform extensive lab tests with the specific material (grey cast iron and cast steel) from which these drums are produced. 

Beside all technical reasons the big advantage of a pneumatic test is, that the steam drums can remain within the line because first we have no additional load for the bearing and only small adjustments (for the connection with the pressurisation unit and the tightening of the man ways for the applied low temperature gas test) have to be done to make the drum ready for a pneumatic loading. The pressurised air is available in every paper mill and even if the maximum pressure does not fit, the use of a compressor or pressure bottles produce no problems. 

The main goal during the pneumatic test (loading and pressure holds) is to have a pre-warning system against any catastrophic failure during the pneumatic loading (gas pressure test).(4)... 

The main reasons for the application of a pneumatic test in conjunction with an AE are... 

During a hydrotest the additional weight of the water superimposes the normal operational stress by steam pressure. The big advantage of the pneumatic test is now, that it is the best imitation of the normal service condition. 

Table 1 Steam drums, which undergo a pneumatic test monitored with AE...

The only meaningful solution is a pneumatic test in conjunction with an AE. Beside the high sensitivity of an AE and its reliability in combination with an established and proven data base, the method can be performed by experienced testing agencies easily and within short shut down period. A lot of 4 up to 9 drums can be tested within one day. 

A study is at present being carried out to check and validate the feasability of acoustic emission monitoring of the pneumatic testing of tanks. This study is being carried out in the context of the CIAPES program. This article gives only a brief summary of the results obtained on various materials, and different types of vessels, under different operating conditions. 

In order to confirm the capability of acoustic emission to detect the evolution of a defect during a pneumatic test, a vessel with a lack of thickness due to the action of corrosion was pressurized pneumatically until burst. 

Some partners of the programme have already obtained the authorization to make in-service pneumatic test monitored by acoustic emission instead of hydraulic tests. 

Tile new Pressure Equipment Directive (P.E.D.) established by the European Commission recognize acoustic emission as a complementary method which can be used to monitored pneumatic test when hydraulic test could not be perform. 

If hydrostatic testing is not considered practicable by the owner, a pneumatic test in accordance with the following procedure may be substituted, using air or another nonflammable gas. 

All pressure vessels must pass appropriate hydrostatic testing before approval for service. For safety reasons, hydrostatic pressure testing is almost always recommended over a pneumatic test. The recommended... 

Pneumatic testing of equipment should only be used when hydraulic testing is impracticable appropriate safeguards, e.g. pre-inspection, reduction of the internal gas space, pressure relief, and use of a blast pit or enclosure, are necessary. 

The national pressure vessel codes and standards require that all pressure vessels be subjected to a pressure test to prove the integrity of the finished vessel. A hydraulic test is normally carried out, but a pneumatic test can be substituted under circumstances where the use of a liquid for testing is not practical. Hydraulic tests are safer because only a small amount of energy is stored in the compressed liquid. A standard pressure test is used when the required thickness of the vessel parts can be calculated in accordance with the particular code or standard. The vessel is tested at a pressure above the design pressure, typically 25 to 30 per cent. The test pressure is adjusted to allow for the difference in strength of the vessel material at the test temperature compared with the design temperature, and for any corrosion allowance. 

Depending on the services, the pipeline will usually be hydrostatically or pneumatically tested. Normally a section is specified for testing from flange point to flange point. Once tested the blank flanges at the ends of the section are removed and the tested portions are permanently connected... 

Preliminary Pneumatic Test. A preliminary test using air at no more than 170 kPa (25 psi) gage pressure may be made prior to hydrostatic testing to locate major leaks. 

Pneumatic testing involves the hazard of released energy stored in compressed gas. Particular care must therefore be taken to minimize the chance of brittle failure during a pneumatic leak test. Test temperature is important in this regard and must be considered when the designer chooses the material of construction. See para. IP-10.6.2(b)(3) and Nonmandatory Appendix B. 

The pneumatic test may be used in lieu of the hydrostatic test for hydrogen systems designed or supported so they cannot safely be filled with liquid, or if the vessel or system cannot be readily dried or is to be used in services in which traces of the testing liquid cannot be tolerated. The substitution requires that the parts of the system, when possible, are previously tested by hydrostatic pressure. The pneumatic test pressure should be 1.25 times the MAWP. 

Clean Agent Visual inspection Pneumatic test of piping Flow test of the piping Fnclosure integrity test Flectrical systems operation properly Discharge test 2001... 

Clean Agent Pneumatic test of piping at 40 psi (276 kPa) for 10 minutes. 2001... 

If the piping is tested pneumatically, the test pressure shall be 110 percent of the design pressure. When pneumatically testing nonmetallic... 

Inspection and testing requirements are covered in detail. Most vessels are required to be hydrostatic-tested (generally with water) at 1.3 times the maximum allowable working pressure. Some enameled (glass-lined) vessels are permitted to be hydrostatic-tested at lower pressures. Pneumatic tests are permitted and are carried to at least IV4 times the maximum allowable working pressure, and there is provision for proof testing when the strength of the vessel or any of its parts cannot be computed with satisfactory assurance of accuracy. Pneumatic or proof tests are rarely conducted. 

The seal between the two wires and the cup, tube, etc shall be continuous. If the seal is questionable, it is subjected to a pneumatic test by introducing an internal air pressure of 4 psi, held for 3 seconds... 

Accident during pneumatic test of storage tanks... 

With a volume-pneumatic test, mechanics can detect defects in the parts due to incorrect replacement parts, incorrect machining, corrosion, or weak springs. Each of these problems can be discovered by such characteristics as early simmer, only a partial lift or leakage after the test. Defects such as inadvertently installing a spring too strong for the set pressure can be detected by short blow-down or chatter. Competent SRV test craftsmen can pinpoint defects with this type of test equipment. 

With a volume-pneumatic test, mechanics can detect defects in the parts due to incorrect replacement parts, inconect machining, corrosion, or weak springs. Each of the.se... 

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