Development of a Qualification Methodology for Volumetric Inspection of Pressurised Welds in Subsea Sensors
Status: Proposal
Date Announced: June, 2023
Project reference: PROP310532
Summary
This Joint Industry Project (JIP) will address the problems that manufacturers of subsea sensors for the oil and gas sector face where full volumetric inspection of critical welds is required by API standards. Currently manufacturers have to either design larger welds than necessary to adhere to standards or use substandard inspection techniques, potentially allowing serious defects to remain in the welds during service. The project in two phases each over 12 months will develop and qualify innovative and improved NDT techniques and procedures specifically designed to detect the types of defects that occur in the small, autogenous electron beam and laser welds that form the pressure boundary of subsea sensors.
The output from the project will be a Best Practice Guide for the sponsors of the project providing detailed guidance for the volumetric inspection of the different types of welds found in subsea sensors. The Guide will include evidence from experiment and modelling that manufacturers can use to support technical justifications for inspection qualification and advice regarding automation and personnel training and certification. The project will align with the requirements of API-6A for Subsea Equipment with a plan to present the JIP findings in the relevant committee.
TWI is inviting a consortium of sponsors for the project from companies in the oil and gas sector who are specifying, manufacturing and operating subsea sensors. The consortium of sponsors will have exclusive access to the Best Practice Guide for a period that the consortium agrees. The project will enable manufacturers and operators of subsea sensors to achieve better compliance with current standards and a more reliable product through improvements in the quality of welds and the reduction of defects with competitive advantage and benefits to safe and continuous production.
Introduction
Subsea oil and gas (O&G) production relies on subsea sensors to provide data for the control of production of a subsea well to the topside monitoring and control station. This data is critical to controlling the integrity of the well infrastructure and to the management of the assets of the field in terms of recovery, production rate and safety. Typically, such sensors are part of the Christmas tree at the wellhead of a completed well for the monitoring of flow, pressure and temperature of flow for effective reservoir production and safety management. The safety and reliability of these sensors and the avoidance of leaks in service are therefore high priorities for manufacturers and operators of subsea sensors.
These types of sensors are usually assembled using autogenous electron and laser beam welding. Currently, manufacturers typically use surface inspection techniques, helium leak and pressure testing for the detection of welding defects. However, according to the API-6A specification, there is also a requirement to perform volumetric inspection of Wellhead and Christmas Tree equipment using either radiography or ultrasonic testing.
Currently lack of access for ultrasonic inspection or large and complex material paths inhibiting radiographic inspection are limiting the coverage for volumetric inspection of a significant percentage of the typically small, autogenous welds forming the pressure boundary of subsea sensors. Manufacturers cannot therefore meet the standards that industry requires for subsea sensors with their current approach to inspection. They are then left with the choice of:
- Having larger instruments then necessary with larger non-autogenous welds in order to meet the volumetric inspection criteria, increasing cost through all stages of the system lifecycle (manufacturing, transportation, deployment and decommissioning), or
- Accept non-conformances and the possibility that potentially serious defects will remain in the welds with the possibility that these may lead to a leak during service. There is therefore a need to develop and qualify improved NDT for the full volumetric inspection of critical welds in subsea sensors.
Project Concept
Smaller welds found in sensors present a challenge for detection of typical flaws by the common non-destructive evaluation (NDE) methods, which limits the application of NDE for quality control. A further complication is that, during various stages of manufacture, access to the weld area is not always possible. This can restrict the application of techniques such as ultrasonic inspection. Likewise, the thickness of a sensor module may increase the radiation path sufficiently to limit the successful application of radiography for weld inspection. Another consideration is applicability of inspection at manufacture. This needs to take into account inspection costs and time (manual vs. automated), personnel training requirements and certification, and recording of test results to be provided by the manufacturer to the purchaser in order to comply with international standards.
There is clearly a need for industry guidance on NDE inspection methods that give a suitable balance of cost, time and quality for pressurised welds in subsea sensors. The requirements to drive down cost and gain industrial acceptance have been the main barriers against implementation of volumetric inspection of pressurised welds in subsea sensors. TWI will review the suitability of the reference standards and investigate the suitability of different NDE solutions, taking into account the above factors. Upon completion of all the NDE investigations, guidelines will be developed covering the use of non-destructive testing (NDT) for inspection of pressurised welds in subsea sensors. Having recognised best practice for NDE will increase confidence in the quality of inspection of subsea sensors. This Joint Industry Project (JIP) will aim to establish best practice in a form that can become an industry standard, and that would reduce cost of quality through development of practical and effective methods and measures to ensure the integrity of sub-size weldments. API subcommittee 17 (Subsea Production Equipment) has invited TWI to update them on progress of this project, through presentation at their periodic meetings and will offer feedback on findings of the best practice guide. This will place the best practice guide in a position where it can be incorporated into relevant industry accepted standards.
Objective
To produce best practice guidelines for the industrial application of a cost effective volumetric inspection of sub-size welds within subsea sensors, with the potential to be included in an international standard, that can be widely accepted by manufacturers of instruments, integrators, oil companies and regulatory bodies.
Benefits
- Increased confidence in performance, safety and reliability of subsea sensors.
- Current weld practices can be retained without costly redesigns to meet current standards. Sponsors gain deeper insight into integrity of own components.
- Identification of short-comings of current oil and gas standards for application to sub-size weld validation.
- Best practice guidelines that will enable manufacturers to know when to implement volumetric or alternative inspections during manufacture, leading to improved safety and reliability of subsea sensors.
- Adoption of a cost effective inspection solution that satisfies the requirements of relevant codes, standards and industry stakeholders and offers potential cost reduction across sector.
If you are interested in finding out more, see the PDF download. If you would like to join this JIP, please contact us.