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The State of the Art of Weld Seam Inspection on Pipes by Automated Ultrasonic System Using Special Composite Transducers Eng. Edson Vasques Moreira Material Engineer, CONFAB INDUSTRIAL S.A. Brazil, NDT, Calibration and Qualification Supervisor Eng. Luiz Francisco Martins de Oliveira Mechanical Engineer, CONFAB INDUSTRIAL S.A. Brazil, Quality Control Manager Eng. Sérgio Ricardo Pinto Ferreira Mechanical Engineer, CONFAB INDUSTRIAL S.A. Brazil, Industrial Manager Contact

ABSTRACT

When we are talking about inspect of manufactured parts with high productivity and reliability, is necessary to use automatized inspection system. If we need to make the inspection by ultrasonic method today, we have a great technological evolution of ultrasonic automated systems for inspection of several applications, like welded and seamless pipes, plates, railroad industry, nuclear components, aircraft, automotive, etc. Nowadays, for welded pipe manufactured in accordance with specification API 5L, we have available systems with high performance level, easy operation and full data acquisition. This paper aims to show to the Non Destructive Testing Community, the technological advances available for weld seam inspection on pipes by ultrasonic method and the state of the art for improving and optimization of this type of inspection system. Said system is composed of a new generation automatic ultrasonic equipment what is based on a 20-channel PC, immersion probes with composite crystals, providing excellent performance, also a series of arrangements which are fundamental for obtaining optimum inspection results. The system was adopted in 1999 by the UOE Pipe Mill of CONFAB INDUSTRIAL S.A in Brasil to inspect pipes in according to specification for line pipe API 5L and several supplementary requirements. This plant is a supplier of welded pipes by SAW process (submerged arc welding) with diameter from 12 3/4" to 48" and thickness from 0,250" to 1,250". It system has been contributing greatly to productivity, quality control, versatility of configurations and applications.

1. INTRODUCTION

CONFAB INDUSTRIAL S.A., is a DST - TECHINT GROUP company. It is the welded pipe supplier in South America leader, also it has made a lot of investments in it facilities in the last two years. Among others equipments, CONFAB installed on DSAW-UOE unit in Pindamonhangaba, São Paulo, Brazil, the most modern automatic ultrasonic system for welded pipe inspection available. This system has a several technical improvements that increased the possibilities the arrangements of the probes used. With the continuous increase of requirements from the customers regarding inspection by automated ultrasonic and the change of the thickness range from 0,250" to 1,250" with diameters from 12,750" to 48", we decided to buy a system that support a sufficient versatility to program in accordance with all types of requirements, also that to assure a high quality and an excellent productivity. This paper summarizes the main technical characteristics of this system, the arrangements and recourses available.

2. PIPE MILL AND EQUIPMENT POSITION

Fig 1: Ultrasonic System Position on the Pipe Mill

The mill, where this system was installed is a pipe manufacturing plant, UOE process, that means U press, O press and cold Expansion. This plant has a high productivity and uses heat rolling plates. After forming, these pipes are longitudinally welded by submerged arc welding in accordance with mainly, API 5L specification and the other special requirements. Please see Figure 1, below.

This plant manufactures pipes with maximum individuals length of 12,4 m or jointers up to 24,0 m. The diameter range is from 12,750" to 48" and the thickness range is from 0,250' to 1,250". The ultrasonic system that we are explaining is located immediately after the cold expansion and hydrostatic testing, that corresponds to the final ultrasonic inspection of the weld seam on the pipe.

3. TECHNICAL CARACTERISTICS OF SYSTEM

The system uses 03 Krautkramer equipments, model USPC 2100, with a total of 20 channels, which is able to work with several types of probes arrangements and configurations.

ITEM	ESPECIFICATION
Method of inspection	Pulse-echo and through transmission.
Speed	Maximum 25 m/min.
Probes	Krautkramer, 4MHz, crystal 9x8 mm.
Apparatus	Krautkramer USPC 2100. 02 with 8 channels e 01 with 04 channels.
Gates	Interface, Indications e Coupling.
Scanning	Longitudinal weld seam.
Delectability	Notches N5 e drilled holes 1,6 mm.
Results	Printed and micro computer.
Others functions	Alarm sonorous and visual and paint gun.
Table 1: Technical Characteristics of system

4. EQUIPMENT AND TRANSDUCERS

4.1 Ultrasonic equipment.
The ultrasonic system for automatic inspection has new conception and technical characteristics that result in a good performance, it's working with speeds of 25 m/min and 14 probes. The USPC2100 can work with 2500 Hz of pulse repetition frequency per channel. This equipment works with multiplex or in parallel mode. Please see bellow the equipment view on the Figure 2 and 3. When it is necessary more than 08 channels, for the synchronization, one equipment works like MASTER and the others work like SLAVE.

Fig 2a:	Fig 2b:	Fig 3a:	Fig 3b:
Fig 2: Ultrasonic equipment USPC 2100 - Gates and Strip options		Fig 3: Ultrasonic equipment USPC 2100 - System and Measurement options

4.2 Transducers
Probes are used immersion with crystals of Barium Titanate with a frequency of 4MHz, dimensions 8x9 mm. The refraction angles normally used are 70, 60 and 45 degree, also all of them work with shoes that guaranty the perfect coupling to several diameters of the pipe. These probes have a divergence angle between 15 to 20 degree and this allows to detect holes with diameters of 1,6 mm and longitudinal and transversal, inside and outside notches N5. Nowadays we are testing a new type of probe made with crystal of composite. It presents advantages over the traditionally used up now. Basically speaking, these composite probes can help the inspection with the echoes and noise reduction without lose the sensibility and the resolution during the inspection. The quantity of gain necessary to calibration using composite probes is 6 dB less than a Barium Titanate probe. Please see the comparison of screens on the Figure 4, when we do the calibration using a drilled hole 1,6 mm of diameter) at 100% of the screen high. The pipe dimension is 20" x 0,875".

Fig4a: W70Z4NE - Composite	Fig4b: W70Z4N - Barium Titanate
Fig 4: Comparative echograms between transducers W70Z4N e W70Z4NE

5. REFERENCE STANDARD

A reference standard is used to calibrate the system using a pipe with the same dimensions that the pipe to be inspected and machining artificial defects, outside and inside notches N5 (longitudinal and transversal) and drilled holes with diameter of 1/16 inches.

Fig 5: Reference Standard

Fig 6: Basic Probes Configuration

6. PROBES CONFIGURATION

The system has several configurations that is easily programmed on the equipment. The probes arrangements is located in accordance with the thickness to be inspectioned, according to requirement of the customers and according to the process. It is possible to use 14 probes scanning the total weld seam length for entire wall thickness, plus a range of 5 mm on each side. One example of configuration we can see on Figure 6, where it is important to remember that other types of configurations are possible and can be quickly changed to maximize the recourses that the system can supply, also to attend specials requirements.

7. SYSTEM AUTOMATION

This system was totally automated through of an installation of a set of electric and electronic recourses that provide a easy way to operate and also reduce the necessary inspector activities. With the automation of the system, the extension scanned was increased and only 100 mm on the pipe edges stay without automatic inspection. In the weld seam of pipe edges are made X-Rays in a extension of 8 inches. Sensors make the probes down also make them to couple automatically when the pipe reach the programmed position. When the probes are adequately coupled the system runs the pipe. This procedure is repeated for all the probes. In the weld seam is made inspection without the inspector intervention and in the end of the pipe, the probes get up automatically. While the scanning the weld seam tracking system guaranties the correct position of the probes, having the weld seam as reference without manual correction. All indications are recorded automatically when the weld seam reach correct position with the respective probe that detected the indication. Please see the Figure 7 that illustrates this automation.

Fig 7: Probes coupling automation

8. INSPECTION SYSTEM CAPABILITY

Basically a inspection study capability constitutes for this type of system, as a minimum, Coverage, Repeatability, Setting parameters, Inspection procedure and Personnel qualification. The coverage shall be checked and if the system physically stop the inspection near the end of the pipe, the remainder of the pipe must be inspected by manual UT or X-Ray. Normally the maximum speed of inspection can be calculated using the following formula below:

Where:	V maximum	= Maximum speed of inspection, in m/min..
	RPFHz	= Pulse Repetition Frequency, in Hz.

Nondestructive inspection system must demonstrate consistent detection of defects and it is important to measure the defect detection performance to an inspection's reliability. Using the fixed parameters like pitch, pulse gap, speed, PRF, etc., after the system is calibrated, the reference standard shall be passed through a minimum of 10 times and when the holes and notches passes through the probe the system has detect all the time. The dynamic run, with same speed of pipe production revels the inspection system's performance for detection of artificial defects. As a minimum, the signal amplitude achieved on the dynamic run shall exceed the alarm threshold setting used for each applicable reference notches and holes. Inspection system which not demonstrate repeatable detection of reference standard shall have similar poor performance in detecting natural imperfections, and in such cases, adjustments to the inspection parameters or equipment should be made to assure repetitiveness defect detection. Other important factors is that the personnel that are responsible for the operation of equipment are qualified and understand the inspection process also work with a qualified procedure by a Level III inspector.

9. CONCLUSION

This new automatic inspection system installed on CONFAB Industrial S.A. can attend the API Specification 5L and also several supplementary requirements. The probes arrangements available in this system, data record and a set of others resources permit to inspect with accuracy technique, providing a excellent assurance, productivity, traceability and reliability.

10. REFERENCES

1. American Petroleum Institute , API Specification 5L, Washington, April 1995.
2. Moreira E V , Schubert H and Walker D, "Optimization of automatic system and multi channels for welded pipes inspection using "Ultrasonic PC-Based Test System", XVIII CONAEND, ABENDE, Rio de Janeiro, Brazil, September 1999.
3. The American Society of Mechanical Engineers, ASME, Nondestructive Examination Section V, New York, 1998.
4. American Petroleum Institute , API Specification 5CT, Washington, October 1998.

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