Guided Wave Monitoring

    Guided wave inspection is performed at fixed inspection intervals prescribed by governmental regulations. Sometimes these intervals are not in line with the maintenance requirements. Since GWT is a surveying tool, guided wave monitoring is required to do in-service testing before a planned shutdown. Ample time is then available to plan the necessary maintenance work long before the actual shutdown takes place. Therefore, total downtime for the installation is reduced.

    The MsS System has a number of advantages compared to GUL Wavemaker and Teletest in guided wave monitoring. Since the MsS system is based on the magnetostrictive sensor (MsS), the benefits of long-range guided wave monitoring with MsS system are:

1. MsS probes are much cheaper than piezoelectric ring probes.
2. The probe is light (less than 0.5 kg for 24-inch-OD pipe), so that the installation work is easy at high level.
3. Easy installation
4. No limitation of pipe size exists because the MsS probes are directly made onsite
5. Only a 25-mm clearance is needed around the pipe in permanent monitoring.
   MsS probes work well at high temperature pipe up to 300°C.

    In MsS guided wave monitoring, the MsS probe is permanently installed at a corrosion- sensitive region of the inspection structure; baseline data are obtained; the structure is periodically tested; and the periodic data are compared with the baseline data to identify structural changes with time.

    The merits of MsS guided wave monitoring compared to inspection are:

1. Quickly obtain new data with the installed probes
2. Data is acquired from the same location of probes
3. Small changes in condition can be readily detected with comparison of baseline data and periodically monitored data
4. Finds defect initiation and growth in geometric features such as weld, support, attachment, etc.
5. No need to remove insulation or excavate soil for the probe installation except for the first time - Allows in-service testing in high temperature or high elevation line.
6. Gives ample time for maintenance work and reduces total downtime