Corrosion sensors and on-line boiler wall inspection

The difficulty of establishing the relationships between fuel quality parameters, boiler operating conditions, and the actual situation at the corrosion sites is one of the most important practical limitations encountered in boiler-tube degradation studies. In the AEB waste-fired power plant, this kind of information is imperative to gain a better understanding of asset life performance and to determine lifetime predictions for boilers operating under higher pressure and temperature.

Project
DNV KEMA supplied and demonstrated several types of corrosion sensor and boiler-wall inspection techniques to AEB stakeholders. These inspections jointly led project participants to well-substantiated conclusions.

KEMCOP®
KEMCOP is a simple corrosion probe that is fitted into the strips of the boiler and can be removed after an agreed-upon period. A number of these special bolt-type test patches are fitted into the boiler, and then the probes are analyzed using microscopic techniques to assess degradation mechanisms at the probe site. The probes can be prepared with different metals or alloys, so that the implications of particular materials’ choices can be assessed. At the AEB boiler, probes of various compositions were systematically exposed for various periods of time at several locations within the boiler. In this way, a systematic overview was acquired.

KEMCOM
KEMCOM is a high-temperature on-line electrochemical corrosion monitor. With this device, it is possible to measure corrosion in real time and to directly correlate the corrosion rate to process conditions. KEMCOM can be utilized in both the superheater section and the furnace section of a boiler. At AEB boiler 36, two identical temperature-controlled KEMCOM probes have been installed to monitor corrosion behavior, with the goal of optimizing firing conditions. The corrosion probes have been installed at different levels within the boiler, on the front and sidewalls of the first pass, to map the corrosive conditions in relation to changes in process (firing) conditions.

KEMBUS
KEMBUS is an ultrasonic method used to measure a boiler membrane’s wall thickness from the outside of the boiler during a plant stoppage. To use the technique, a boiler’s insulation has to be removed and the boiler tube has to be full of water. Once scaffolding is put up inside a boiler, measurement work can start as long as it does not interfere with other activities. The method is faster and more accurate than commonly used ultrasonic firesidescan methods.

Benefits
The combination of these three methods, together with in-depth knowledge, helps plant owners to efficiently plan and optimize their boiler maintenance strategies, and therefore, contribute to asset life extension at reduced operating costs.

Project coordinator
>  DNV KEMA, the Netherlands

Project details
>  Duration: February 2006 – ongoing