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HIC and Steel Cleanliness Inspection Author:Joachim Staudt, AG der Dillinger Hüttenwerke, D - Dillingen Co-Author:Ulrich Sauer, Krautkrämer GmbH & Co. oHG, D - Hürth Contact

Today during steel production the quality is controlled by comprehensive laboratory tests, including destructive tests, to meet the requirements of the customers.

The makers of pipelines, e.g. more often require "HIC" - resistant steels (HIC = hydrogen induced cracking), including the corresponding test documentation. HIC samples are used to test the resistance of steels against HIC induced cracks. The HIC samples are stored in a saturated hydrogen sulphide solution for a certain time, afterwards these samples are artificially aged in a simulation process.

The destructive metallographic test is today often substituted by a non-destructive ultrasonic immersion test.

The DILLINGER HÜTTE (DH), in co-operation with KRAUTKRÄMER (KK), has taken a new computer controlled ultrasonic immersion test system with automatic evaluation in operation

This test installation is used at the DH for the detection of HICs as well as for the determination of the macroscopic cleanliness of steel samples.

Series of samples are scanned in one course, but each single sample is evaluated individually afterwards.

The samples or HIC testing are 20 - 75 mm wide, max. 100 mm long and up to 60 mm thick. The samples for determine the cleanliness are 400 mm wide, approx. 200 mm long and up to 20 mm thick.

Requirements for development of the new test system

• Modular structure
  • Increase of proper function and availability
  • Easy to adapt to the future technical development
  • Easy maintenance (e.g. remote maintenance by modem)
• Best possible detection sensitivity
• High test throughput
• Testing of several samples in one scan, with individual analysis of each sample
• Parallel inspection and evaluation of different sample series
• Automatic calculation and display of test results and archiving of this data
• Scan area: ³ 550 mm x 550 mm
• Test speed: ³300 mm/s
• Track index: £ 0,1 mm, adjustable in steps of 0,04 mm
• Frequency range: 0,5 to 25 MHz
• Depth resolution: £ 0,01 mm
• Flaw detection limit:0,2 mm Æ FBH
• Test thickness range: £ 60 mm
• Evaluation of sample series: automatically

Structure of the test installation

The machine consists of the following main components (fig. 3 - 6):
• 3 axes scanner with control
• Ultrasonic instrumentation with immersion probe
• Control and evaluation electronics for data acquisition (PC)
• Data processor for evaluation of single samples, independent from the simultaneously running test (PC)
• Colour monitor and printer

Fig 1: Block diagram	Fig 2: Definition of HIC-cuts and characteristic values	Fig 3: US- and control-electronics
Fig 4: Scan unit	Fig 5: Probe, probe holder with samples	Fig 6: Evaluation PC


The programming of the scan programs, the adjustment of the ultrasonic electronics and the operation of the test installation is performed by the data acquisition PC.

The evaluation is performed by an additional independent evaluation PC, connected by LAN

Description of components

1. Mechanics

   max. scan-area:	600 x 600 mm
   min. scan index:	0,1 mm, adjustable in steps of 0,04 mm
   max. scan speed:	300 mm/s
   X, Y-axis:	Stepper motor control with gear
   Z-axis:	manual adjustment

2. Ultrasonic unit
   • Computer-controlled ultrasonic electronics KRAUTKRÄMER VIS (VIS = VME-Integrated-System)
   • VME-Bus system, installed in a 19"-cabinet
   • 1 ultrasonic channel with a band width: of 0,2 - 25 MHz
   • 4 gates
   • DAC
   • All US-Parameters controlled by PC
   • A-scan-display on the monitor
   • Immersion probe: 15 MHz
   • Detection sensitivity: 0,25 mm KSR
   • Separate evaluation PC
3. Data acquisition and evaluation
   For each matrix point the following data is recorded:
   
   • Entrance echo amplitude and time of flight (TOF)
   • Flaw echo amplitude and time of flight (TOF)
   • Backwall echo amplitude and time of flight (TOF)
   • X- and Y-co-ordinates

   For evaluation the following variants can be displayed:

   • A-Scan
   • C-Scan, showing a sample series or a single sample
   • B-Scan showing a sample series or a single sample
   • Display of the chosen virtual cuts in a sample
   • Histogram
   • Zoom
   The HIC - specific characteristic values CAR, CLR, CTR and CSR are calculated automatically.

   Also the corresponding test protocols are generated automatically.
   (Example fig. 9).

   Fig 7: A-scan 0,5 mm FBH

   Fig 8: C-Scan of test samples (0.5 mm and 1.0 mm FBH)

   Fig 9: C-scan of series of samples

   Fig 10 : Test protocol

   Thus the production accompanying quality control is automised, the test results are available earlier than before. Since the raw data is stored, the samples can be evaluated according to different algorithms and specs, without rescanning!

   A clear indicator for the real importance of these tests and the necessity to automise them, is the number of samples, which had been tested in the past 3 years:

   	HIC samples	samples for cleanliness test
   1997	11.457	132
   1998	12.955	177
   1999	13.776	389

   This great amount of samples can only be managed and documented within the daily operational routine with an automatic test installation like the presented test system.

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