Boilers suffer from many forms of degradation while in service. Water wall tubes can incur a range of issues, from hydrogen damage, pitting, ash and soot-blower erosion, graphitisation, under-deposit corrosion, thermal fatigue cracking and creep damage. These types of degradation may impact on the normal running of a company’s facilities, and, ultimately, the operation of the business.
Regular inspections are key in order to maintain proper boiler functioning and prevent further damage or failure. However, the traditional method of inspecting boiler water wall tubes for loss of wall thickness is acknowledged to be very slow and expensive. It requires many thousands of ultrasonic thickness readings, spaced several feet apart in elevation, to be taken, which is a very time-consuming process.
That same traditional inspection process also requires the boiler to be scaffolded and the tubes (usually) to be cleaned to bare metal in the areas where the readings are to be taken, thus lengthening the process even further.
As part of its commitment to innovation, Applus+ has been researching solutions for cheaper and faster inspections of water wall tubes. With more than 100 years’ experience in the field and a vast network of state-of-the-art laboratories, Applus+ has succeeded in developing VertiScan, a time and cost-saving alternative, driven by Remote Field technology.
The VertiScan System is used to rapidly scan the water walls of a boiler during a scheduled outage so that repair decisions can be made proactively. Up to five tubes can be scanned at once, at speeds of up to 5m (15 ‘)/min. The robotic (TubeCAT) crawler can climb 100’ up/down the water wall and handle up to 1/4″ of scale between the tubes, with results presented immediately on a colour map showing areas of degradation. All indications found are checked with visual and ultrasonic techniques, where tubes are accessible.
The technique is sensitive to all types of wall thinning, including:
- Hydrogen damage
- Under scale pitting and graphitisation
- Flame and soot blower erosion
- Blistering and local overheating
- Creep damage (thermal fatigue)
- Elephant skin, rhino hide
- Dents and gouges
- Internal and external pitting
The cost to scan all four walls of a boiler is generally far less than the cost of an emergency shut-down due to tube failure. Many of our clients see the VertiScan system as an efficient and cost-effective alternative, and are already testing and implementing the process at their sites.
Colour map showing scan results, i.e. areas of degradation