- Non Destructive Test on Journal Bearing & Thrust Bearing Pads of KWU Design Steam Turbine During...

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TECH. CIRCULAR NO.X-49.

Dated : 10.08.1994.

SUB :- Non destructive test on journal bearing & thrust bearing pads of KWU design steamturbines during maintenance inspection.

Enclosed please find herewith write-up No. STE-TF-066-SG on the above Subject for yourreference and use.

NDT ON JOURNAL BEARINGS AND THRUST BEARING PADS OF KWU DESIGN STEAM TURBINESDURING MAINTENANCE INSPECTION.

1.0 SCOPE :-

This test instruction is applicable for non- destructive test of babbit lining of journal bearingsand thrust bearing pads during maintenance inspection. Only the service exposed bearingsare to be tested as per this instruction. For inspection of new bearings and rebabbitedbearings, Plant Standard No. HW 0850195 is to be followed.

2.0 EXTENT OF TEST:

Each bearing is to be subjected to 100% inspection for:

a) Surface defects on the total surface of babbit lining by means of dye penetration test.

b) Bonding defects between the babbit metal and the bearing shell by means of ultrasonictest.

3.0 SURFACE CONDITION :

The areas to be inspected must be free from any foreign matter. Babbit surface should nothave any unevenness, which impair the validity of the tests.

4.0 DYE PENETRATION TEST :

4.1 Test parameters:

Dye penetration test is carried out in accordance with Corporative Specification No.AA0850131 using dye penetration or fluorescent penetrate. The penetrate, cleaner anddeveloper should match each other. Penetration dwell time must be at least 20 minutes.Interpretation of the indications is done immediately after drying of the developer and after20 minutes of developing time. The indications are recorded in the test certificate.

4.2 Assessment of test results: No crack is permissible on the babbit surface. IsolatedPorosity upto f 1.5 mm can be allowed.

5.0 ULTRASONIC TEST :

5.1 Test Equipment and Probes

The ultrasonic equipment used for the test should

a) operate by means of pulse- echo method.



b) be equipped with a calibrated gain (dB) control.

c) conform to IS :12666 / ASTM E – 317

Ultrasonic test is to be performed with normal probes matching the equipment used. Probesare to be of 2 MHz nominal frequency and provided with a protective membrane. Diameter ofthe probe should correspond with the diameter of the journal bearing as shown in Table-1.

TABLE-01

Diameter of bearing (mm) Probe diameter(mm) d < = 100 06

100 < d < = 600 10

600 < d 24

5.2 Setting & Sensitivity :

The distance calibration and sensitivity setting is carried out with the help of test blocks (Figure-1 and Figure –2 ) of babbit metal similar to that of the bearing lining.

5.2.1. Equipment Setting.

a) First back echo from test block set to 80% of screen height.



b) Correction factor = (+) 6 dB (difference between the flat surface of the test block andthe curved surface of the bearing, also refer Fig.1 of Annexure-1) .

The figures in Annexure – 1 also show the screen indications for good and bad bonding ofbabbit metal.

5.2.2 Recordable Indications:

All indications >= 50 % of the screen height are to be recorded refer Figure.03 of Annexure –1). 5.3 Test Procedure : Ultrasonic test on the babbit metal is to be carried out withapproximately 20% overlap between two successive scanning tracks.Recordable indications,if any, are to be noted on a test report format as shown In Annexure – 2.

5.4 Assessment of test result :

5.4.1. Permissible non- bondage for cylindrical and two lobe bearings is as per Annexure-3.

5.4.2. For thrust bearing pads and annular thrust rings, maximum permissible non-bondage<= 2% of the total surface area.6

6.0 DOCUMENTATION :

The results of dye penetration and ultrasonic test are to be recorded on a test report formatas shown in Annexure-2. In case permissible indications are exceeded, FES section of SteamTurbine Engineering may be consulted.



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