Recently we have been involved in pricing a project destined for BP Shah Deniz Stage 2 Project in Baku, the Caspian Sea.
The work involves the Phased Array Testing of Stainless Steel butt welds 60mm thick, a total weld length of 75 meters.
All of the previous welds on the project had been radiographed but these where only up to 40mm thick. The supplier / fabricator decided that because of the plate thickness an alternative to x-ray was to be suggested to BP.
On the grounds of safety alone the justification for an alternative method of non destructive testing was apparent.
As part of the process we put together a list of reasons comparing phased array and radiography, pros and cons.
Like I said, safety first
- Possible to dose the radiographer if issues arise
- Potential HSE involvement
- Transportation of large sources
- Inspection area to become a controlled area
- Chemicals involved with processing
- Equipment size is small and portable
- No HSE Notification required
- No form of radiation used
- No chemicals
- No Monitoring of workers
- No controlled area required meaning fabrication work can commence at the same time as testing
Radiography can be affected by many factors, the material thickness or characteristics can cause an issue given that this was 60mm thick. Other issues could be
- Film batch issues
- Chemical Issues
- Exposure time
- Mis-aligned exposure
- Film movement during the exposure
- Source movement
Phased array doesn’t use any chemicals other than coupling, either water of some form of off the shelf item such as Sonagel. The equipment can be completely setup away from the job utilising weld simulation software such as ES Beam Tool. The results from phased array are apparent immediately meaning that any scan issues can be rectified before leaving the job.
Phased array data can be stored on a memory stick device for easy sharing or using modern methods such as FTP storage. This means that within minutes the images can be placed online for the clients representative to second view data.
Phased array is accepted now in most of the standards that require x-ray such as API, ASTM, ASME, AWS.
So How Accurate is Phased Array ?
If you take x-ray again it is though that the probability of detection for discontinuities is in the region of 80 to 90%. X-ray produces a density image that will show you the length and position of an indication.
Phased Array however is a view-able ultrasonic inspection that has different possible views on screen in real time. Sectoral scans, C Scans, B Scans, Conventional A scans can all be viewed and manipulated for best interpretation. This gives you an image from the top and also the side. This reveals the length, height, and depth of a flaw.
Phased Array UT has a detection probability of 95 – 97%. Couple this will conventional UT probes and Time of Flight Diffraction (TOFD) this is in the high nineties.
Phased Array sizing has now been carried out down to 0.5mm. This is beyond almost all codes / standards.
Phased Array like all forms of non destructive testing has its down sides. But when compared to conventional radiography it is a far better form of NDT. Its quicker, safer and offers many quality positives as detailed above.
Responsive are investing a lot of time into the best use of Phased Array. We are now asked continuously when carrying out radiography at Lillyhall if we can compare the results with Phased Array, we are more than obliging to undertake this type of work.
Read more on Shaz Dinez
Around $28 billion in capital investment will be required to produce the gas and transport it to the Georgia-Turkey border. From there, additional pipeline systems will deliver 6 bcma of gas to Turkey and a further 10 bcma of gas to markets in Europe, in a route known as the Southern Gas Corridor. Shah Deniz gas will travel 3,500 kilometres, to elevations of over 2,500 metres, and over 800 metres below the sea.
Shah Deniz Stage 2, one of the largest gas developments in the world, will help increase European energy security by bringing Caspian gas resources to markets in Europe for the very first time. .
The current concept for Shah Deniz Stage 2 includes:
two new bridge-linked offshore platforms.
26 gas production wells which will be drilled with 2 semi-submersible rigs.
500 km of subsea pipelines will link the wells with the onshore terminal.
upgrade of the offshore construction vessels
expansion of the Sangachal terminal to accommodate the new gas processing and compression facilities.
Read more at http://www.bp.com/en_az/caspian/operationsprojects/Shahdeniz/SDstage2.html