The nature of steam reforming means that tubes within are consistently subjected to intense temperature cycling and pressure that, over time, causes creep damage and cracking. The longevity of these reformer tubes is generally estimated in relation to how long they’ve been in use.
However, although this has been the norm for an extended period of time, it has distinct disadvantages. The major one being that as there’s no easy method of assessing the condition of the tubes they’re either retired too early – meaning an expenditure that wasn’t necessary – or too late, leading to costly repairs and asset downtime.
Naturally, operators are keen to move to a condition-based assessment as and when technology advances enough to do so. But up until recently there hasn’t been a solution sufficient to overcome the many challenges that allow for effective tube life predictions based on adequate analysis of their condition.
These include:
- Reformer tubes are hard to reach and dirty
- Their magnetic properties alter over time, meaning technology has not, up until now, been able to return reliable, high-quality inspection data
Non-destructive testing (NDT) methods, such as ultrasonic testing (UT), profilometry and eddy current testing (ECT) have only been used with limited success. ECT in particular is impacted by the changes in the magnetic properties of the tubes and are unable to penetrate deep enough to detect cracking in the inner diameter. Therefore cracks that exist evolve, breaching the inner diameter of the tube and progressing to the outer. Once this occurs, leaks and/or pipe failure follows.
Enter the advanced technology of eddy current array (ECA), the next generation in NDT methods.
How does ECA differ from other electromagnetic inspection techniques?
ECA is an advanced form of ECT. It uses multiple elements arranged side by side, covers a far wider surface area, has improved detection abilities, delivers more consistent result and, importantly, can be customised to reach hard to access areas. This is proving massively advantageous when it comes to inspecting the condition of difficult to reach reformer tubes.
Another crucial aspect is that ECA allows for a low-frequency inspection containing magnetic bridges that can saturate the material of the tubes, therefore overcoming the penetration issues of ECT, and allowing for the detection of cracking induced by creep.
The reality of using ECA inspection probes
Inspection probes have been developed solely for this application. They enable the capture of data of tubes with outer diameters ranging from 50.8mm to 165.1mm, and can penetrate walls as thick as 15mm. In addition, data can be returned on up to 140mm of tube surface in a single pass.
Cracking from creep occurs both longitudinally and circumferentially in reform tubes, and ECA inspection probes have been proven to detect both. However, the depth at which this can be effectively determined is dependent on the thickness of the tube wall.
Circumnavigating the tubes is assisted by the probe being mounted on wheels and having detachable cables. The data recorded can then be referenced to an encoded position and time, and is represented as an easy to read C-scan image.
Benefits
The potential to move towards a condition-based assessment rather than one that’s time-based has many positive repercussions.
- The ability to detect cracks that have been out of the remit of previous technology gives operators a far more accurate view as to the necessity of replacing reformer tubes. The current reality of simply not knowing is expensive in multiple ways. This includes the replacement of pipes unnecessarily or having to shut down production to carry out costly repairs when a leak or failure occurs.
- Tubes can be scanned while the reformer is in service. Inspection is relatively quick, and with reliable data it’s possible to monitor progress of creep damage and to put strategies in place to ensure integrity of the asset.
While the process is by no means perfect as of yet, the advancement in technology is a huge leap towards full condition-based assessment. The information provided by ECA inspection allows for operators to plan proactively for maintenance and downtime, therefore saving time and significant outlay.
Considerable funding and effort is being expended into the continued improvement of this cutting-edge technology, and it will only be a matter of time before ECA inspection for reformer pipes becomes the norm.
Perth-based Nexxis are committed to the provision of the latest advancements that address industry needs. As opposed to simply offering equipment for sale and hire, they instead use an innovative approach whereby they work with customers to determine necessary challenges to be overcome. This allows for a fluid solution based on the dynamic needs of any given operation.
Such advanced partnering is only possible due to the highly experienced team behind the scenes.
Source: https://nexxis.com.au/case-study-the-use-of-eddy-current-array-in-reformer-tubes/
