Measuring up to the compliance challenge

With integrity rising up the pipeline operators’ safety agenda, the search is on for new technologies and best practice to enable compliance and smarter ways of managing the maintenance of these vast infrastructures on and offshore. Tony Holliday, CEO of CorDEX Instruments, argues the case for ultrasonic NDT technology.

The Distribution Integrity Management Final Rule, issued by the the US Department of Transportation’s Pipeline & Hazardous Materials Safety Administration (PHMSA), came into force in August 2011. The new rule requires operators of gas pipelines to conduct risk assessments on those systems to establish the pipelines’ fitness for service and initiate resolution to any risks identified.

Key to the long-term viability of a pipeline network will be tools and technologies that can quickly and effectively determine the extent of its degradation. Preventative maintenance programmes will have an important part to play and there are a significant number of benefits to taking this approach. Not only do they result in fewer unscheduled shutdowns, but undertaking this type of maintenance can lower insurance premiums. It can also save pipeline operators money by giving them the ability to manage capital expenses with planned purchases, eliminating emergency buying where there is less negotiating power with a supplier.

There will likely be a role for ultrasonic testing, as that method eliminates the need for shutdowns and gives more comprehensive and accurate results than other methods. However, given the combustible nature of the materials within these pipes, there is a need for intrinsically safe devices to come to the fore.

Pipeline failure is often attributed to corrosion and defective welds along with testing and record keeping all play a role. The majority of the 2.5 million miles of US pipelines which transport oil and gas are cast iron and were installed more than 50 years ago.

Currently, these pipelines are operated by approximately 3000 companies and fall under the safety regulations of PHMSA. The US is not facing this problem alone; pipeline owners and operators across the globe are grappling with corrosion, excavation damage and issues around repair of pipelines made of obsolete materials such as cast iron, copper and vintage steel.

There is also growing demand for improved testing of materials used in ageing offshore assets. The use of ultrasonic devices for non-destructive testing (NDT) has become more common in recent years as equipment has increased in capability and decreased in price. Ultrasonic NDT devices work by creating a pulse of high-frequency sound, generally in the range of 2.5Mhz to 10Mhz, and then measuring the return, a process that makes it possible to measure anything from the simple thickness of a material, to corrosion and even weld or flaw inspection. The use of ultrasonic NDT devices is attractive because their non-invasive nature does not require a plant shutdown to obtain a measurement.

An ultrasonic device operates by creating a pulse or series of pulses of sound, then measuring the return of those pulses back to device. These pulses and echoes are sent and received by a piezoelectric transducer. Simple thickness measurement devices, for example, measure the time of flight of the sound wave between the pulse and the echo. The time between the pulse and the echo equates to two times the material thickness when multiplied by the known material velocity value. The pulser/ receiver in this example excites the transducer, which fires a sound wave into the pipe and measures the time it takes for the rear surface echo to return to the transducer.

Ultrasound is perfect for measuring thickness, because it requires access to only one side of the material being measured. In the case of a pipe, the pipe can even be filled with fluid and in operation, which means a service stoppage is not required to conduct the test. A simple thickness measurement can be enhanced by using predefined max/min alarms to help de-skill the task of identifying problem areas.

Using an ultrasonic tester for corrosion testing is more complex and requires a more capable device. Corrosion testing generally requires the transducer to be moved in a snake motion within a 100mm x 100mm box on a specific area of interest.

The device will monitor the thickness reading across the path and provide the user with a max, min and average reading so that it is possible to define areas of pipe wall thinning quickly and easily. Ultrasonic NDT devices are attractive because of their non-invasive nature. However, deploying this kind of device within a hazardous/classified location has implications for safe use that even NDT inspectors may not be fully aware of.

Intrinsically safe devices are designed to limit power both at the source (battery) and component level to prevent a spark or heat source powerful enough to ignite a gaseous atmosphere. Even the casing and neck strap of an intrinsically safe device must be manufactured from a certified anti-static material to prevent a spark. Ultrasonic testers that are intended for use within hazardous/ classified areas should comply with the specific requirements and be certified as intrinsically safe, based on third-party standards such as ATEX, NEC and IEC/Ex.

Equipment development

Since its formation CorDEX Instruments has focused exclusively on developing equipment to perform NDT on pipelines and equipment located in hazardous areas. It recently introduced a new intrinsically safe ultrasonic tester for corrosion detection, the UT5000, which for the first time incorporates the functionality required to implement and maintain a predictive maintenance program into an intrinsically safe tester.

The UT5000 uses RFID technology – permanently placed passive tags which use radio frequency to communicate data to a device each time a reading is taken – to locate and log up to 1000 measurements, each linked to a specific location, date and time.

The UT5000 can be used for days or weeks in the field before the data is downloaded, providing accurate corrosion analysis and helping to predict potential failures.

A corrosion mode helps identify thinning spots, and MultiECHO technology improves measurement accuracy on uneven surfaces. The handheld device is easily portable and ideally suited to retrieve readings from over-ground sections of pipe quickly, but can also be utilised underground.

Designed for rugged environments, an over-moulded body protects a 3.1in RGB TFT colour screen with backlight. The dual-element, 4MHz transducer is adjustable up to 10Hz with accuracy of ±0.05mm. This accuracy level stands true in both single point and continuous measurement mode, delivering unprecedented accuracy and flexibility to classified area NDT inspectors. The tester features both single point and corrosion modes, allowing the user to identify specific points of thinning in a pipe wall.

One of the issues identified as contributing to pipeline failures in the US was incomplete records. To address this, CorDEX developed CorDEX Connect – a software programme which can be downloaded to any PC – to collect and organise the data obtained on site, ultimately giving the inspector a detailed account of the condition of the pipeline at any specific location.

With CorDEX Connect, those responsible for monitoring pipeline safety can use data collected by anyone in the field to create predictive maintenance programmes. Using the software’s trend analysis capabilities, trouble spots can be identified from measurements taken over multiple visits. It also tracks calibration status, alerting the user to suspect readings. When the tool is sent for calibration, real-time tracking allows the user to track its transport and calibration status.

Only comprehensive testing and good maintenance can ensure the vast ageing infrastructure in the US and around the world are less prone to integrity issues. The new federal safety rule will most certainly drive a new wave of risk assessment activity, requiring significant investment by pipeline operators.

Now will be the time for operators to look at the options available to evaluate the extensive pipeline systems. As pressure mounts for better pipeline maintenance, the technology is in place to enable these regulations to be fulfilled. Investment in comprehensive risk assessment and monitoring of pipeline integrity will help ensure that future pipeline failures can be averted and will help operators comply with regulations.

The technology is now available to implement what may ultimately be a procedure that enables long term cost savings. Preventative maintenance programmes are the best step forward to alleviate some of the cost issues associated with pipeline preservation on this scale and the use of intrinsically safe technology can ensure this is carried out as safely as possible. OE

Tony Holliday, chief executive of CorDEX Instruments, started his career as an instrument and electronics engineer and invented a number of ATEX and CSA certified intrinsically safe products. Before joining CorDEX Holliday spent ten years in product development roles and two years 

Dunlin isolation at length   A pipeline isolation and valve change out operation has been completed by Stats Group on Fairfield Energy’s Dunlin Alpha platform in the North Sea. The workscope included the replacement of two 24in launcher valves on the oil export line from Dunlin to Cormorant Alpha and marks the specialist company’s longest duration remote isolation to date.    The in-house designed Remote Tecno Plug which provides double block and bleed isolation was used for this job. The technology eliminates the need for communication tethers or specially modified pig trap doors and allowed the old valves to be removed without the requirement for tether management.   In preparation, Stats carried out a piggability study on the oil export line and trialled the Remote Tecno Plug (RTP) onshore with a client witnessed factory acceptance test using a purpose-built test fixture simulating the offshore pipeline configuration.   The shutdown was scheduled for up to 80 days, with the RTP serving as the primary isolation on the export pipeline. Dave Vernon, Stats’ head of intervention and isolations, confirmed the plug was ‘constantly monitored and remained stable and in location for 72 days while maintenance operations were completed’.   On-site, the RTP was loaded into the launcher before pigging to the set location with a mixture of water and nitrogen. The plug was tracked and positioned using through-wall communication, with an extremely low frequency (ELF) radio control system setting and then monitoring the plug throughout the isolation prior to valve change-out and maintenance activities starting. Once the new valves were installed a bespoke 24in in-line weld test tool with an extended body and additional locking module was provided to test the newly made-up flange joints. The extended body allowed the tool to straddle both flanges of the new valves.    As part of the planned maintenance scope, the operator also replaced a 1.5in pig signaller which Stats pressure tested with a separate 1.5in flanged weld test tool. On successful testing of all valves and flanges the RTP was unset and reverse-pigged back to the launcher for demobilisation.

Line insulation monitoring    The latest innovative subsea products from Viper Subsea are the V-SLIM subsea-deployed line insulation monitor and V-LIM line insulation monitor.    The V-SLIM (pictured) provides a simple and convenient diver/ROV deployable method of fault finding and locating electrical problems within the subsea electrical distribution network where faults cannot typically be identified from topsides. It immediately detects the presence of an earth leakage fault and provides a measurement of insulation integrity and loop resistance of any connected circuit, and can identify whether any earth leakage is upstream or downstream of the unit, helping to pinpoint the location of the problem. Compatible with existing subsea control systems, V-SLIM is designed to help avoid unplanned interventions by monitoring and trending electrical system integrity.    The V-LIM, designed for use on AC floating systems, is a self contained, panel mounted, microprocessorcontrolled precision device specifically optimised to monitor the integrity of electrical umbilical cables. Available for integration into new topsides equipment or for retrofitting into existing installations, the V-LIM is designed for accurate monitoring of insulation resistance, voltage, current, loop resistance and polarisation index of the umbilical and connected subsea equipment. The data gathered can be used to analyse the rate of deterioration of system electrical insulation and when this is likely to result in a system failure. It can also help identify the probable type of system failure, says Viper Subsea.

Girth weld checks   A new digital radiography system launched by non-destructive testing specialist Applus RTD was designed primarily for fast-production pipeline inspection work, and is suitable for the inspection of girth welds on lay barges and onshore new construction pipework. With the RTD Rayscan the x-ray source and detector rotate around the exterior of the weld, producing a real-time digital radiographic Double Wall Single Image (DWSI) picture.   Direct image processing, allied to dedicated software, makes it possible for direct interpretation of the weld, including changes to the appearance of the image allowing easier identification and recording of defects and their size. Initially available for use on pipes ranging from 2in to 12in diameter, the Rayscan system uses a small, collimated x-ray beam, short exposure and lower energy levels compared to conventional techniques and has full lead shielding to protect against radiation hazards.   Also new from Applus RTD is the IWEX 3D (Inverse Wave field Extrapolation) technique, hailed as the future of ultrasonic testing by Dennis Zaal, manager of the company’s Europe and Middle East application centre. ‘Existing UT techniques present the measured signals in an abstract format, showing the interaction of the ultrasound beams with the object instead of only the object itself,’ explains Zaal. ‘IWEX provides a reconstructed image of the inspected object, providing vital clearer data compared to traditional techniques, resulting in increased accuracy in both sizing and positioning of the defect.    ‘Additionally, increased probability of detection is expected,’ he says. ‘Images made with IWEX can be seen as a reconstructed cross-section of the object only, much like a CT-scan or an MRI scan in the medical field, meaning what you see is what you get.’