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Small Diameter Tube and Pipe Inspection with Time-of-Flight Diffraction (TOFD)


Introduction

Small diameter tube and pipe inspection can be difficult. Challenges include the fact that pipe-to-pipe clearance is typically very small; access to the pipe is limited to only one side; and the wall thickness and diameter are quite small, making typical phased array (PA) probes unusable. Because of the size of the probes and scanners, radiography was typically preferred over phased array and conventional ultrasound methods.

Phased array offers several advantages over radiography when it comes to inspecting small diameter tubes and pipes. Often, a series consecutive inspections are required, so the system that is being used must be able to provide repeatable results one inspection after the other. Small diameter tube and pipe inspection systems also must fast and capable of quickly moving from one inspection area to the next. The Olympus COBRA® scanner was optimized to overcome the traditional limitations of phased array inspection for small diameter tubes and pipes with features including:

  • Slim scanner, PA probes, and wedges enable complete coverage of the pipes since only a small pipe-to-pipe clearance is required to perform a 360° scan.
  • The scanner adheres to the pipe or tube using a spring mechanism that enables 360° coverage, even when only one side of the pipe or tube is accessible.

Solution

The COBRA scanner phased array solution offers a fast, practical system for small diameter pipe and tube inspection. By using ultrasonic technology, users can avoid the inherent difficulties and disadvantages that accompany radiographic inspection, such as safety concerns, regulatory issues, the technique’s slow speed, and the need to clear people out of the inspection area during testing.

Olympus’ 80° TOFD wedges further enhance the capabilities of the COBRA solution. While keeping the advantages of the COBRA scanner discussed above, the TOFD technique is a cost-effective solution that is very sensitive to volumetric defects in small diameter pipes.

Scan plan of the TOFD inspection of a 5 mm thick pipe using the 80° COBRA wedges and 15 MHz transducers.
 

COBRA TOFD wedges and transducers assemble in the scanner and on the part.
 

TOFD is a well-established technique that has a long history of use for general weld inspections. It has proven to be a fast and easily deployable method with an excellent capacity for sizing. One of the inherent strengths of TOFD for detection and sizing purposes is its relative indifference to the orientation of defects because of its primary use of diffracted versus reflected energy. 

Ultrasonic transducers are positioned on each side of the weld; one transducer sends the ultrasonic signal into the material and the other receives reflected and diffracted ultrasound from discontinuities and geometric reflectors. TOFD provides a wide area of coverage with a single beam by exploiting ultrasonic beam spread theory inside the wedge and the inspected material. When the ultrasound signal comes in contact with the tip of a flaw, or crack, diffracted energy is cast in all directions. Measuring the time of flight of the diffracted beams enables accurate and reliable flaw detection and sizing, even if the crack is off-oriented to the initial beam direction.

The kit of COBRA TOFD wedges includes one pair of flat wedges plus nine pairs of curved wedges to cover pipes with an OD range of 1.05 in. to 4.5 in. The wedges are designed to fit ST1 probes with 3 mm diameter elements. Note that the use of these wedges will increase the minimum clearance required for the use of the COBRA scanner compared with the phased array option.

Scan of a weld with the cursor positioned on a clean area; the A-scan shows a good lateral wave and back wall signal with no indications in between.
 

Scan of a weld with the cursor positioned on a discontinuity; the A-scan shows a signal between the lateral wave and the back wall.
 

Equipment Used

  • OmniScan® MX2/SX flaw detector
  • COBRA solution kit (U8750053, COBRA scanner for pipe inspection (probes and wedges are not included))
  • 15 MHz TOFD transducer
  • ST1 -80L wedge kit for the COBRA scanner, 1.05 in. to 4.5 in. OD pipes (COBRA-A-ST1-80L, U8710172)
  • WTR-SPRAYER-4L or other suitable couplant delivery (U8775153)
  • OmniPC™/NDT SetupBuilder/TomoView™ software (optional scan plan and analysis software programs)

Conclusion

The COBRA scanner with TOFD technology provides a cost-effective, efficient, and reliable testing method capable of meeting the challenges associated with inspecting small diameter tubes and pipes. When paired with the OmniScan SX UT flaw detector, the end result is a comprehensive record of inspection data conveniently stored in an electronic format that can be re-opened and analyzed at any time. The evolution of the discontinuities encountered during an inspection can be monitored over time, enabling inspectors to determine a trend and plan for preventive maintenance.

Although radiography is the most commonly used technique for this application, the ultrasound techniques discussed here offer many advantages in terms of safety, the probability of detection, and the speed of inspection.

Summary of key benefits

  • Cost-effective weld inspection alternative.
  • Precision sizing and measurement.
  • When combined with the OmniScan flaw detector, meets code requirements for encoding and full data collection.
  • Covers standard pipes ranging from 1.05 in. to 4.5 in. OD.
  • Operates in limited access areas.
  • Can record the position of the probe at all times to measure the length of discontinuities.
  • Precise 32 steps/mm encoder.
  • Provides steady and repeatable results.
  • Lightweight and easy to install for fast configuration from one weld to the next.
  • Waterproof, rust-free, and CE-compliant.

Olympus IMS

应用所使用的产品
TomoView是一个基于PC机的性能强大、变通灵活的软件,用于设计、数据采集、视图显示,及超声信号的分析。
OmniScan MX2的双通道传统超声模块(UT2)可用于TOFD(衍射时差)检测。它具有高脉冲发生器电压(340 V)、增强的PRF功能和改进的信噪比(SNR)。
OmniPC软件是用于分析OmniScan数据的非常经济有效的选配项目。 软件所提供的分析工具与OmniScan的机载软件相同,而且更具灵活性,因为它可以在个人电脑中运行。
轻便的单组Omniscan SX探伤仪装有一个方便用户阅读的8.4英寸(21.3厘米)触摸屏,可提供性价比很高的检测解决方案。OmniScan SX有两种型号:SX PA和SX UT。SX PA是一个16:64PR仪器,它与仅使用UT技术的SX UT一样,配备有一个用于脉冲回波、一发一收或TOFD(衍射时差)检测的常规UT通道。
OmniScan MX2现在不仅可以与带有一个UT通道的相控阵模块(PA2)及一个用于TOFD(衍射时差)检测的双通道常规超声模块(UT2)配套使用,还可以使用一些创新型软件程序。这些软件程序更进一步提高了业已相当成功的OmniScan MX2平台的性能。
COBRA手动扫查器与OmniScan X3探伤仪相结合,用于对小直径管道进行周向焊缝检测。COBRA小直径扫查装置可容纳两个PA探头,对外径范围在0.84至4.5英寸的管道进行检测。
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