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Cracking in Ceramic Diesel Particulate Filters


EPOCH XT testing ceramic

Application
Detection of internal cracking in ceramic diesel particulate filters.

Background
The use of ceramic particulate filters is well established as a method for removing environmentally dangerous soot and similar particulates from diesel engine exhaust, especially for diesel engines used in trucks and buses. These filters have the form of large cylinders, approximately 100 mm to 300 mm (4 in. to 12 in.) in diameter and 150 mm to 350 mm (6 in. to 14 in.) high. They are commonly made of cordierite, silicon carbide, or ceramic in a fine honeycomb pattern. As the hot exhaust is forced through the porous filter under pressure, soot particles collect on the surfaces of the honeycomb channels where they then break down or oxidize due to heat.

These complex ceramic structures can potentially crack during manufacturing, handling, or in service, causing reduced performance or failure that can cause both environmental and engine damage. Ultrasonic testing can quickly and nondestructively detect internal cracking in both new and used ceramic filter elements. The technique usually requires access to only one end of the cylinder.

Equipment
This test can be performed with both conventional flaw detectors and phased array instruments Any of the Epoch-series flaw detectors (EPOCH LTCEPOCH 600, EPOCH 650 or Epoch 1000) can be used with a low frequency contact transducer such as an A601S-RB or V601-RB (500 KHz). The OmniScan SX can also be used with the aforementioned transducers. A soft polymer membrane on the face of the transducer is used to couple sound energy into the filter without the need for liquid couplants that could be difficult to remove. The Advanced Filter option (standard on the Epoch 1000) can be helpful for improving signal-to-noise when testing larger filters by improving the instrument's low frequency response. Phased array testing can be performed with the OmniScan or Epoch 1000 and 1.5 MHz probes such as the 1.5L16-A4.

Procedure
Using firm hand pressure, the transducer is coupled to the end of the filter. High frequency sound energy propagating as plate waves travels through the ceramic honeycomb, reflecting off the far end if there are no discontinuities. If there is a crack parallel to the end surface, an echo will be received ahead of the point on the display representing the far end of the filter. If there is a crack that is tilted with respect to the ends, there may be no direct reflection but the echo from the far end will disappear.
 

In the example below representing a setup with a flaw detector and an A601S-SB transducer, the left screen image represents a typical echo pattern from an undamaged filter. The peaks at the left side of that waveform represent reverberations of the outgoing sound pulse, and the echo at the right side represents the reflection from the far end. There should be no significant echoes in the zone in the middle that is marked by the red gate. The right screen image represents an echo pattern from a filter that is cracked just past its midpoint. The backwall echo to the right of the gate has disappeared because sound energy is no longer reflecting from the far wall. The transducer can be moved to as many points as desired on the face of the filter to check for cracks at other locations.

Typical Backwall Echo from Good Filter

Typical Backwall Echo from Good Filter

Typical Midwall Echoes from Cracked Filter

Typical Midwall Echoes from Cracked Filter

The specific instrument setup for each type of filter should be established through the use of a known good setup standard that is used to optimize the echo from the far end. By identifying the echo pattern from a good filter and looking for changes, a trained operator can quickly and reliably identify echo variations that correspond to internal cracks.

Phased Array Testing

OmniScan Testing

Phased Array can offer cross-sectional imaging of filters from either sectorial or linear scans. This can aid operator visualization of flaws. Automated testing has also been implemented using larger array probes and specialized fixturing.

Olympus IMS

应用所使用的产品
OmniScan X3系列的每台探伤仪都是一款功能齐备的相控阵工具箱。其创新型全聚焦方式(TFM)和高级相控阵(PA)功能助力您充满信心地识别缺陷,其性能强大的软件功能和便捷的工作流程有助于提高您的检测效率。
OmniScan MX PA仪器可以进行手动和自动相控阵检测。这款仪器具有以下功能:功能齐备的A扫描、B扫描、S扫描和C扫描显示,以及高级实时数据处理。仪器可被配置为16:128晶片、16:16M、16:64M、32:32和32:128。
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。
EPOCH 650仪器是一款常规超声探伤仪,具有优质的检测性能和广泛的适用性:可用于许多检测应用。这款简单直观、坚固耐用的仪器脱胎于广受欢迎的EPOCH 600探伤仪:EPOCH 650仪器添加了一些EPOCH 600探伤仪没有的功能。
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