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Development of a high sensitivity ultrasonic phased array Non-Destructive Testing (NDT) method for the early detection of creep damage (Type IV cracking) in alloy steels used in high temperature, high

Periodic Report Summary 1 - CREEPTEST (Development of a high sensitivity ultrasonic phased array Non-Destructive Testing (NDT) method for the early detection of creep damage (Type IV cracking) in alloy steels used in high temperature, high)

Project Context and Objectives:
The project is aimed at developing a field implementable inspection system for detection of early stage Type IV creep damage in thermal power plants which use creep strength enhanced ferritic (CSEF) steels for high temperature operation. Type IV damage is of particular concern to power plants as the damage starts as small voids at the fine-grained heat affected zone (HAZ) which is very difficult to detect by existing industrial non-destructive testing (NDT) methods except at the surface.

Metallurgical replication is done on the outside surface of components and is able to find micro-level voiding damage under ideal circumstances. But no validated system for evaluating the condition of the metal subsurface currently exists on the open market. Power plant operators are desperate to have a method of evaluating the internal condition of components as it is unclear at present whether the damage starts on the outside surface and propagates into the pipe or whether initiation is internal and by the time the manifestation is detected on the outside surface the remaining life of the component is dangerously close to the end. This uncertainty is further exacerbated by several incidents worldwide where components have failed by Type IV creep damage well before the estimated end of their operation life. This makes power plants extremely nervous as the personnel, environmental and financial costs of a catastrophic Type IV failure could be severe.

The objective of this project is to undertake a theoretical assessment of the problem with regard to ultrasonic sensitivity to creep damage at an early stage. The consortium considered the damage level expressed in a scale developed by VGB at the position 3a and 3b as the goal for detection in the CreepTest project (see deliverables D1.1 for explanation of the problem and D1.3 for the specification generated for this project). Using specimens which contain varying level of creep damage provided by the Consortium end-user Scottish & Southern Energy the Consortium is aiming to generate the instrumentation (to include the transducers, pulser-receivers and software) to become sensitivity to the very small cavitation that is characteristic of creep damage.

Project Results:
The project is aimed at developing a field implementable inspection system for detection of early stage Type IV creep damage in thermal power plants which use creep strength enhanced ferritic (CSEF) steels for high temperature operation. Type IV damage is of particular concern to power plants as the damage starts as small voids at the fine-grained heat affected zone (HAZ) which is very difficult to detect by existing industrial non-destructive testing (NDT) methods except at the surface.

Metallurgical replication is done on the outside surface of components and is able to find micro-level voiding damage under ideal circumstances. But no validated system for evaluating the condition of the metal subsurface currently exists on the open market. Power plant operators are desperate to have a method of evaluating the internal condition of components as it is unclear at present whether the damage starts on the outside surface and propagates into the pipe or whether initiation is internal and by the time the manifestation is detected on the outside surface the remaining life of the component is dangerously close to the end. This uncertainty is further exacerbated by several incidents worldwide where components have failed by Type IV creep damage well before the estimated end of their operation life. This makes power plants extremely nervous as the personnel, environmental and financial costs of a catastrophic Type IV failure could be severe.

The objective of this project is to undertake a theoretical assessment of the problem with regard to ultrasonic sensitivity to creep damage at an early stage. The consortium considered the damage level expressed in a scale developed by VGB at the position 3a and 3b as the goal for detection in the CreepTest project (see deliverables D1.1 for explanation of the problem and D1.3 for the specification generated for this project). Using specimens which contain varying level of creep damage provided by the Consortium end-user Scottish & Southern Energy the Consortium is aiming to generate the instrumentation (to include the transducers, pulser-receivers and software) to become sensitivity to the very small cavitation that is characteristic of creep damage.
Description of work performed and main results:
The scanner design to implement the technique on the steam pipe component as specified in deliverable D1.3 is complete and ready for fabrication. Fabrication is being held until the design (shape & size) of the transducer is finalised. The theoretical and experimental work to design the transducers is ongoing using a range of specimens that are available to the project. The specimens available to the project have been captured in deliverable D1.2 and more have since been used in the project, supplied by the Consortium end-user. The pulser-receiver instrumentation is being developed to drive the specialist transducers being designed. The software for control of the prototype (scanner and instrumentation), acquisition of data and visualisation for interpretation is being developed in parallel.

The key development in the project is the transducers and the technique to become sensitive to the creep damage when it is at an early stage. Work is ongoing on this front and will likely continue to the end of the project and the field trials. At the end of the project the capability of the prototype system to detect and characterise the creep damage will be made.

The Consortium is engaged in an ongoing effort to collect as many specimens containing early stage creep damage as possible. The strategy for this is captured in D1.2 but is constantly evolving. The proposed method to artificially generate early stage damage has not been successful for a number of reasons which include the size of specimens, capability of existing standard creep testing machines to implement interrupted tests and the duration of the test. The Consortium is however continuing with efforts in the hope that some specimens can be generated in this method. However, good specimens containing service induced creep damage have been provided by the Consortium end-user and materials from previous projects have been useful in the development work.

One condition in which the system is falling outside of specification is the weight of all components. The scanner design is within the weight limit but the present forecast for the instrumentation is that it will likely be heavier in total (signal generator, receiver, laptop, amplifiers) than the specified amount. Since the Consortium is limited to integrating the equipment that is commercially available in the market this limitation may have to be accepted for the first iteration of the prototype. However this is not expected to prevent he system from being implementable in the field and the Consortium expects to trial the system as planned.

Potential Impact:
The Consortium expects to generate a prototype system which will be field implementable. The data collected both on the specimens used for development and the field trials should allow a good assessment of the project technique. Should the capability be deemed sufficient then it will be proposed for further industrial trials towards full qualification for inspection tasks.
List of Websites:
www.creeptest.com