LESER Deutschland Standard Functional Tightness Test (Cryo) Content

Transcription

1 Page 1/10 Content 1 Purpose Scope Range of Application Normative Background Terms and Definitions Test Equipment Test Procedure Acceptance Criteria Inspection Certificate EN Purpose This (LDeS) describes how company LESER tests spring loaded safety valves for functional tightness (tightness between disc and seat) at cryogenic temperatures (below -146 C / -231 F). The test is selected by Option Code M80, then executed and documented in a LESER inspection certificate EN Scope This standard applies for the production site Germany (LESER DE). 3 Range of Application Safety valves with a set pressure of up to 155 bar / 2248 psi and up to a size of DN200 / 8 can be tested on a test bench. The test temperature is always below -146 C / -231 F during the test. The realizable configurations are described in LID

2 Page 2/10 4 Normative Background This LESER standard applies for in-production tests. There is no international standard for this describing a procedure for an in-production test. LESER s test is based on the standard DIN EN concerning the type approval. The reqirements for tightness test at cryogenic conditions has been developed and realized corresponding to DIN EN The acceptance criteria for the functional tightness conform to the standard and are shown in chapter 8. 5 Terms and Definitions 5.1 Leakage Rate Leakage rate is the amount of the test medium that, as a result of a pressure difference, flows through a hole in a certain time. - q L is the leakage rate and the common unit is: q L = mbar * l * s -1 - Example: Thus, a maximun allowed leakage rate means q L zul 1* 10-4 mbar * l * s -1 with a tightness requirement where at standard pressure in 10 4 mbar bzw. ca. 2,7 h not more than 1 cm³ test gas may flow through the leakage.

3 Page 3/10 6 Test Equipment 6.1 R & I Flow Chart Figure 1: shematic figure of the test procedure 6.2 Medium Test Medium Helium 4.6 (cooled down to below -146 C / -231 F) is used as test medium for testing the functional tightness Cooling Medium Liquid nitrogen is used as cooling medium for the test safety valve. At the same time, liquid nitrogen is used for cooling down the test medium helium.

4 Page 4/ Testing Device The tightness test is made with a leak indicator PhoeniXL 300 (mass spectrometer). Technical data: Max. inlet pressure 15 mbar Smallest detectable helium leakage rate: - in vacuum mode 5* mbar l/sec Max. displayable helium leakage rate: 0,1 mbar l/sec Measurement range 12 decades In order to guarantee a constant vacuum in the valve s blow-off room, an auxiliary vacuum pump is used. 6.4 Test Pressure The test pressure is calculated with (0,9*p0) 1bar. Set pressure is p0. The tightness test is made by means of a vacuum test. For the test, the ambient pressure in the blow-off room of the valve is reduced by 1bar, and from 1 bara to 0 bara.

5 Page 5/10 7 Test Procedure Before starting the test at cryogenic conditions, the safety valve is set to the required cold differential test pressure at room temperature. (acc. to LGS 0202) The test procedure at cryogenic conditions is as follows: 7.1 The safety valve is clamped on the CRYO test bench (vertical position) 7.2 The safety valve is cooled down The inlet area of the safety valve is purged with liquid nitrogen and cooled down at normal pressure to guarantee a test temperature of below -146 C / -231 F during the leakage measurement. The temperature is taken directly in front of the safety valve at test point t1. Figure 2 (area framed in red is cooled down to test temperature) Figure 3: R & I flow chart for process step cooling down (area marked in red)

6 Page 6/ Before tightness test, let the safety valve actuate once with helium. The safety valve must actuate within the setting tolerance of +3%. Figure 4: R& I flow chart for process step actuate safety valve (area marked in red)

7 Page 7/ Tightness Test Automatic Reduction to Test Pressure sec.flushing out the outlet with 6 bar compressed air to wash out the helium from the outlet which leaked during actuation of the valve. Afterwards, the outlet is closed with a seal flange Connect helium leakage detector to the seal flange. Figure 5 (vacuum test setup) Start the vacuum test. The outlet of the safety valve is evacuated from an atmospheric pressure (1bara) to a vacuum (0bara). After reaching the vacuum, the leakage can be measured The measured helium leakage rate is determined after 20 seconds and reported in SAP If the leakage rate deviates from the acceptance criteria acc. to chapter 8, the safety valve must be handled acc. to the LESER quality management system.

8 Page 8/10 8 Acceptance Criteria The allowable leakage rate for the seat tightness at cryogenic conditions is defined on the basis of DIN DIN EN specifies the leakage rate in 3 mm3/s DN. For the detection of the leakage rate by means of test medium helium and vacuum test a conversion is made from cm³/min into mbar l/s. For the classification of the leakage rate, table 2 shows the number of bubbles. The number of bubbles is a calculation value and is not determined at the test bench. The leakage rate is shown and documented in mbar l/s. Nominal size Allowable leakage rate acc. to DIN EN Leakage rate in cm³/min Leakage rate in mbar l/s Number of bubbles per minute DN25 / 1 4,5 7,6* DN40 / 1,5 7,2 1,2* DN50 / 2 9 1,5* DN80 / 3 14,4 2,4* DN100 / ,0* Table 2: Acceptance criterion

9 Page 9/10 9 Inspection Certificate EN

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