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RMS2 High Temperature Corrosion Mapping

  • Remote access ultrasonic inspection
  • High productivity 17 m²/8 hr shift
  • Very high accuracy scanning
  • Inspect up to 200°C

This application note describes an inspection trial with the RMS2 on assets with elevated temperatures. The trial was conducted on a heat exchanger with a surface temperature of 200°C. There was no cladding on the area being inspected.

A similar high-temperature trial had been attempted before under simulation conditions with a heat mat on a pipe with a nominal thickness of around 8 mm. However the simulation was not indicative of on-site conditions.

The primary reason is due to temperature variations in the thin pipe material, particularly when a continual flow of water from the RMS cooled down the surface, reported to be around 50°C in the vicinity of the RMS probe holder when scanning. This prompted the on-site trial.

Key Benefits:
  • Automated / remote access UT scanner
  • High probability of corrosion detection with up to 0.5 mm scan grid
  • Import inspection data to CMAP
  • Range of scanning heads
  • Field proven durability & reliability
  • No paint removal required

Task: Inspection of Heat exchanger for hydrogen sulphide (H2S)

The on-site trial was conducted at a refinery on an in-service heat exchanger for hydrogen sulphide (H2S) product. The surface temperature of the asset was measured at several locations with measurements between 191 and 200°C. Prior to inspection, the target area was cleaned with a wire brush to remove scale and surface rust.

NDT Inspection Heat Exchanger

Equipment: RMS600 Corrosion Mapping Scanner

An RMS2 600 was used to inspect the inlet end of the heat exchanger of between 2-3m in diameter with a nominal thickness of 35mm. Although the inspection surface was not cylindrical, and its length between the flanges was about 810mm, the RMS2 600 could traverse between the 5 and 7 O’clock position when the safety line I-rings were removed.

The water supply was started before attaching the RMS to the surface. This maintains a constant supply of coolant to the wheels. Once attached, the water would flash boil on the surface, resulting in a cloud of steam around the RMS. There are also videos available of the RMS in operation.

RMS corrosion mapping

Equipment Setup:

The trial was conducted using the standard RMS water column probes with the 25mm and 75mm probe holders; both worked well and provided reasonable A-Scan echoes and a corresponding C-Scan. Notice in the C-Scan image there are several dark blue areas. These relate to weld of internal supports, scattering the sound thus reducing the amplitude of the reflected signal.

A variety of scans with different resolutions was conducted, all with virtually the same results. In this application, it is recommended that the scanner speed is slowed down to around 300mm per second, too quick, the water column wouldn’t stabilise. Also to maintain a reasonable water seal, a high tension on the probe holder is required meaning that a standard 730mm/s travel speed will result in vibration. Several scans were conducted during the 2-3 hours of use with a maximum duration of the RMS on the surface of 30 minutes.

C-scan view


Once removed, the temperature of the RMS was measured with a typical body temperature of around 50°C and a peak temperature of around 90°C on the wheels. The magnets were around 80°C (well within the acceptable range) and the tractor drive belt around 50°C. A cooldown period of around 5 minutes is recommended between each 30 minute inspection duration. Being sealed, the water supply could also be used to further cool down the wheels and body of the scanner.

The heat exchanger trial is a successful demonstration of yet another application of the RMS. The inspection of high-temperature assets is an application that the HydroForm and equivalent irrigated phased array systems would not be possible, primarily because of the larger volume water column. It has been reported through on-site activities that the maximum temperature of an asset that can be scanned with the HydroForm is 115°C. For such applications, the narrow water column of the RMS is superior and the resulting C-Scans, the obtained results.

C-scan view

Thank you

Silverwing acknowledges Oceaneering for their invitation to the trial and for supplying the C-Scan data.

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