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Corrosion under pipe supports and trunnions (Long Range Phased Array)
Finding corrosion in difficult-to-inspect areas has always been a challenge.
Corrosion at pipe supports and trunnions is one of the leading causes of topside-process piping failure.
 
Trunnions
Pipework-support trunnions are common in petrochemical installations, where short lengths of structural-steel tube are welded to process pipework as a means of support. 
Applus+ RTD has responded to this challenge and developed a new way of inspecting these areas: Long Range Phased Array (LRPA). 
With the advances in ultrasonic phased array imaging, transducers and beam modelling, the patented* Long Range Phased Array system allows Applus+ RTD to improve on the application of phased arrays, leading to higher resolution and detection capabilities. 
The transducer, wedge and focal laws are tailored for each chosen application and coupled with an encoder that provides the means to capture data in the axial direction as the component is scanned in the circumferential direction. 
The resultant image has the features of a C-scan with distance and amplitude displayed, which therefore allows for the detection of defects under a welded trunnion support in a hard-to-reach area. This method is a major step forwards in the assessment of pipe supports and inner welded sections.
 
The solution
The LRPA uses a single transducer to inspect under the pipe’s trunnion support (there is therefore no need for two, synchronised transducers). In addition, the LRPA is capable of inspecting up to 2.0m. 
A UT inspection method was chosen as this would facilitate delivery to the point of interest. 
The first stage involved conducting a visual assessment of the surface to see if excessive corrosion was present. The transducer coupling point could then be relocated for the inspection, requiring in some cases only a light surface dressing providing that the surface was sufficiently clean for acoustic coupling. 
This composite ultrasonic beam is sensitive to surface corrosion and quickly identifies corrosion within a trunnion assembly. This provided the possibility of taking a detailed baseline survey using the highest-resolution direct-measurement inspection tool available on the market.
 
The results
 This novel NDT application has proved to be a useful tool for the client and reduces the need for high-energy radioactive sources on site, thereby closing off work faces and creating large, barriered exclusion areas. It also provides a means to quickly assess fitness for purpose.  
A team of two ultrasonic technicians was deployed, and each inspection image recorded against a master report sheet.
 
Reduced risks:
A rapid, medium-range ultrasonic screening method for use on trunnion supports. 
LRPA provides a rapid screening of pipework and is particularly effective in cases of restricted access due to supports or similar obstructions (e.g. clamps and pipe supports).
 
Applications and key features: 
o   Rapid inspection of inaccessible components such as trunnions, pipe supports, saddles and clamps
o   High sensitivity to reflectors on both internal and external surfaces
o   Very high probability of detection
o   Potential for rapid corrosion screening and imaging
 
Verified method: 
The inspection method had previously been field-tested on samples with verified results, and also referenced against pipes with known features.  
The scan images provide details of the location, severity and dimensions of the corrosion site.
 
Responsiveness:
Applus+ RTD can offer inspection services in any location and provide almost-immediate results such that an assessment of inner-pipe condition can be made.
 
 
 
 
 
 
 
 
 
 
 
 
 
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