The application of Automated Ultrasonic Testing (AUT) for the construction examination of pipeline girth welds has grown dramatically in the last decade. The use of AUT has primarily been driven by the need to identify critical lack of fusion flaws in narrow gap shallow angle groove welds, difficult to detect with traditional radiographic (RT) methods. In addition, the adoption of fracture mechanics based acceptance criteria has created a need to accurately determine the size of these flaws and the potential AUT inaccuracy around this.
The process of qualifying AUT system performance is well documented in numerous publications and for offshore pipeline construction is outlined in Det Norske Veritas (DNV) documents OS-FS 101 and RP 118. The application of Immersion Ultrasonic Testing (IUT) is however not as well covered as many other components of the process.
The IUT technique is something that has been recently introduced by Exova, a world-leading specialist in laboratory testing services, as part of the AUT validation procedure for girth weld inspection.
The testing service is particularly relevant for discovering smaller defects as a result of the high accuracy robotics and enhanced immersive testing environment. An increased number of defects can be identified because of the service, such as cracking, porosity, incomplete penetration, inclusions, lack of sidewall fusion, and related defects that can compromise the pipeline’s girth weld strength.
It’s vital that any defect in the welds are detected, accurately located, sized and reported quickly and that’s why leading oil company Chevron worked with Exova, ensuring enhanced inspection detection and sizing capabilities. The technology brings Chevron, and others in the industry, a confidence that the pipeline welds are free from critical defects.
The IUT sits between the examination of deliberately flaw seeded test welds examined by the AUT system under qualification, complementary Non Destructive Examination (NDE) techniques such as RT and physical sectioning of the known flaws.
This whole process can be time consuming and expensive and will often become a critical path activity during pipeline design and qualification. In the past, lack of diligence in the process, unexpected results and the availability of qualified facilities to do the work has led to project delays or the need to waive critical tasks such as the IUT in order to meet construction timelines.
As IUT has been around for decades and is widely used for aerospace forgings and other applications it was surprising that so few facilities were in a position to offer this particular service to an acceptable technical standard.
Exova has a worldwide extensive IUT experience meeting all the requirements for these industries. There are however some oil and gas requirements that are unique for this sector. It was clear that this was perceived as a niche requirement and no one saw a business opportunity to pursue it.
Additionally, there seems to be a lack of clarity about the role IUT plays in the AUT qualification process and almost a ‘fear’ that the differences between the two ultrasonic approaches in some manner will diminish the accepted performance of AUT. We see IUT as filling two functions:
It confirms the length of the flaws for sectioning and provides a second data point to ensure sectioning takes space in the correct locations.
Standards talk about sectioning ‘white space’ areas where no AUT calls have taken place to validate detection performance. The IUT approach allows us to ‘see’ any potential flaws that may not be detected by the AUT and section those areas in order that the pipeline operator can better understand what may be missed and left in constructed girth welds by any particular AUT system.
As a global operator, Chevron needed to identify more qualified assets around the world to ensure that it could access the services it needed. Exova as a global provider of independent laboratory services, was already engaged with the operator at multiple locations providing high quality flaw sectioning and reporting services.
Exova also had IUT experience related to other industries and applications. It made sense for the parties to work together to develop, qualify and establish available IUT facilities at multiple locations close to where a lot of pipeline qualification work was taking place.Case study
Work initially began on the project at Exova in the Netherlands, and test rings were submitted for examination.
Exova took the Chevron requirements and performed a structured qualification effort initially for carbon steel pipe and welds that resulted in a standardised and qualified procedure that meets the Chevron requirements, but more importantly serves the functionality required of the AUT qualification process.
In addition to the base qualification, time and effort was allocated to experimenting with ring thickness to demonstrate that this does not have the impact in sensitivity that many believe. A calibration process was also designed that constructs signal characteristics and thresholds closely mirroring those used in the AUT system to ensure as near possible like-for-like examination conditions.
The available procedure can be applied for any kind of girth weld diameter and wall thickness as well as any material, Carbon steel or CRA’s. Once the facility in the Netherlands was qualified the standardised qualification approach was transferred to the Exova Houston laboratory and repeated.
The actual IUT hardware was not standardised as its qualified performance allows flexibility for different global facilities to access suppliers that may be closer to local markets. This will be the process as additional Exova facilities seek qualification, potentially in Singapore and elsewhere.
Exova has dedicated the Spijkenisse, Netherlands, facility as the development centre for future procedures and AUT validation expertise. The team is currently evaluating new technologies and software functionalities to further support the oil and gas industry.
This project provided multiple benefits to both parties involved. For Exova, it created and expanded the business opportunities, offering a greater access to pipeline contractors that require the IUT section of the AUT qualification. To operators, such as Chevron, it offers a wider market capability allowing the business to ensure all of the technical qualification stages can be accommodated within project time schedules.Authors:
Sander van Nieuwenhuijzen - Exova
Mark Seiwald – Chevron Energy Technology Company
John O’Brien – Chevron Energy Technology CompanyExova
Exova is a world-leading specialist in laboratory testing services to the private and public sector. Exova has over 30 years of experience in the testing and certification industry, from aerospace to automotive, pharmaceuticals to polymers, and food to fire safety and energy. The company operates from 110 facilities in 24 countries and employs more than 3,500 people across Europe, North America, South America, the Middle East and Asia/Asia Pacific, firmly establishing itself as one of the most respected organisations of its kind in the world.
For further information please visit: www.exova.com