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Weldline Inspection System for Submerged Arc Spiral Welded Pipe by Ultrasonic Method Dr.D.Dutta & Rajesh Bose M/s. International Testing & Inspection Agency - Calcutta, India Contact

The present day tube industry employs a wide variety of manufacturing processes to manufacture tubes used for varied range of industrial application. Each process produces tubes whose surface finish,dimensional tolerances and imperfections are characteristic of the individual process. In order to ensure good quality control during the stages of manufacture and the subgequent customer acceptance, it has been necessary to develop non-destructive testing systems for the inspection of steel tubes manufactured by different processes. The present paper deals with weld line inspection system for submerged arc spiral welded pipe by Ultrasonic method

1. ON-LINE STRIP EDGE ULTRASONIC EQUIPMENT

Prior to welding the strip into the pipe form, each edge of the strip is subjected to the following ultrasonic inspection procedure :

The strip is ultrasonically examined for laminations over a width of 25 mm along its longitudinal edges. Two 15 mm diameter pulse echo probes on each edge are used for this examination, and the probes are applied to the side of the strip which will be on the inside of the Finished pipe. "I lie equipment will detect along the edge of the strip, a lamination whose length and width are both greater than 15 man.

The strip edge equipment consists of two trailing arm assemblies mounted downstream of the leveling rolls and positioned such that the I inch wide hand covered by the two probes on each edge is referenced to the edge slitting line. Air purges are mounted in VEE formation on either side of the probe assemblies to remove the ultrasonic coupling water prior to welding The two pairs of ultrasonic probes (i.e. two on either side of the strip) are connected to a four channel electronic unit mounted on a base plate, which is attached to the strip feed table housing, Two paint guns, one on either edge of the stripper mounted approximately 300 mm from the slitting line to mark the longitudinal position of detected strip edge imperfections Solenoid valves, paint containers and control equipment are mounted on the same base plate as the electronic unit, The electronic equipment is arranged to monitor the occurrence of signals prior to tile first back wall echo and also to monitor the signal amplitude of the first back wall echo. This is achieved by a min gate system in the electronic unit. The sensitivity of each channel on the electronic unit is adjusted such that the first back wall echo amplitude is 2 cm. display (Fig. 1) screen height. The paint gun units and audible and visual alarm are actuated when: -

Fig 1:

1. An ultrasonic signal occurring within the first gate i.e. prior to the first back wall echo exceeds the equipment trigger level, which is set to 50% of the first back wall echo amplitude i.e. 1 cm.
2. When the amplitude of the first back wall echo falls below 50% of its normal level i.e. 1 cm.

For demonstration purposes, the equipment will produce a reject signal at the above sensitivity level from an 8 man diameter flat bottomed hole machined halfway through the strip thickness.
A demonstration test piece used for this purpose is as shown in figure 1.
Note: At one end of the test piece (0.375" thick), 5% of the thickness has been removed to facilitate the electronic equipment gate setting to the minimum strip thickness tolerance
To facilitate tire determination of coupling failure, coupling monitor failure indication for cacti pan of probes has separate audio tones.

2. CENTRE SCAN EQUIPMENT

tire body of the strip is checked for laminations and for this purpose two Pulse echo Ultrasonic probes are scanned between the spiral welded seams across a 450 min hand oil the center axis of the strip. The equipment is required to detect the presence of any laminar imperfections greater than 200 min in length and 15 men in width. A reciprocating twin probe unit is mounted on the central ram of the final ultrasonic station, which is capable of automatic application on to the pipe surface. The two scanning probes are connected to a two channel electronic equipment which operates in the same manner and at the same sensitivity level as the edge equipment i.e. a min late system to monitor defect signals prior to the first back wall echo and also to monitor the signal urine first back %%all echo. The equipment will detect a 200 min tell,, defect or greater by detecting the presence of a laminar defect on a number of successive scans, determined by:-
• The surface speed of the pipe under test ,
• The probe spacing, and
• the reciprocating speed of the probes.
When this occurs the paint gun mounted on the fixed assembly of the reciprocating unit will be operated along with audio and visual alarms Tile defect and coupling monitoring indications have separate audio tones to facilitate the determination of coupling failure.

3. WELD TEST EQUIPMENT

The full length of the spiral weld seam on each pipe is examined by a six probe ultrasonic unit, excluding 10 inch at either end of the weld seam. Means are provided to automatically track the weld, i.e. maintain each probe to weld distance constant within well defined limits. This is achieved by using an eddy current weld sensing probe coupled to an hydraulic servo system. ln the event of automatic weld tracking failure manual tracking system is available. The water Irrigated ultrasonic probes are arranged in an XI configuration (see Figure 2) consisting of two longitudinal defect seeking probes, two transverse defect seeking probes and two transverse coupling monitoring probes.

Fig 2: Ultrasonic probe configuration ---X I.

Compling monitoring facilities exist to check the operation of each testing probe. The two longitudinal defect seeking probes monitor the coupling conditions by coupling to one another. The two transverse defect seeking probes are checked for coupling efficiency by the two separate receiver probes mounted on the longitudinal defect seeking probe blocks The equipment is calibrated against a reference standard,
The longitudinal defect seeking probes are calibrated to both internal and external parallel sided longitudinal notches (N5 depth) on both sides of the welded seam (see Figure 3.).

Fig 3:


The transverse defect seeking probes are calibrated to a 1/16" diameter hole drilled through the center of the welded scam. The transverse defect seeking probes are also required to detect ( at the 1/16" hole calibration ) a transverse notch through the welded seam reinforcement of N5 depth + height of crown on the external surface. Two further 1/16" diameter holes are provided on the test sample to facilitate the gate setting of the transverse channels (figure 4),

Fig 4:

A 4-channel event recorder operates automatically during each pipe test and also doling tile calibration check. The following are recorded

1. Longitudinal flaw signals,
2. Transverse flaw signals.
3. Coupling failure,
4. 4 Start/Stop of each pipe test.

When the equipment indicates the presence of a weld defect audible/visual alarms will operate along with a paint marking system to indicate the location of the indication and by which probe system it was detected i.e. longitudinal or transverse .

All indication from the weld testing probes are re-checked for reproducibility by reversing the pipe back and checking the original indications.

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