Boiler unscheduled outages can cost thousands in equipment repairs, as well as consequential and production losses. To prevent this it is critical that all boiler components be regularly inspected and tested. This is generally in most countries a legal requirement as catastrophic failures often lead to deaths.
It is critical that the boiler economisers, evaporators, reheaters and superheaters with auxiliaries be inspected for fly-ash erosion, sootblower erosion, corrosion and mechanical defects, and that critical thick walled components transporting the high temperature steam to the turbines be properly inspected and tested.
We can assist with the compilation of a scheduled boiler inspection scope of work, the execution of all detailed inspections up to the pressure test and completed data books.
|Non Destructive Testing Services|
NDT - Visual Testing (VT)
Visual testing is the observation of a test object or specimen, either directly with the eyes, or indirectly by utilising optical instruments, by an inspector or technician to evaluate the presence of surface anomalies, or an object's conformance to a specification.
Visual examination is the most basic non-destructive testing method, which precedes and is used in conjunction with any othere NDT method. Visual inspection is a method that ranges from simply looking at a part to see if surface imperfections or defects are present and visible, to using video inspection systems and small diameter borescopes to reach into areas with limited access.
The portable videoscopes combines light weight with reliability and ease of use with advanced features to allow inspections in various positions and conditions.
NDT - Radiographic Testing (RT)
Radiography is one of the most widely established NDT methods and involves the use of penetrating X-ray or gamma radiation to examine material defects depicted on the appropriate industrial film. Radioactive isotopes or X-ray tubes are used as sources of uniform radiation. Small changes in material thickness or density have a substantial effect on the intensity of the pernetrating radiation, thus non-uniformities are indicated on the radiographic image as lighter or darker areas on the film.
- Conventional Radiographic Testing: Utilization of conventional equipment to perform radiography as required. This technique requires for the area where radiography has to be done to be evacuated during the testing period. This is done with Ir-192 or Se-75 sources and X-ray machines.
- Pro-Rad - Close Proximity Radiation: Utilization of additional safety equipment to allow for radiography to be done 24 hours per day with only a limited area evacuated and barricaded. This allows for normal construction work to continue with only 3m radius closed off for radiography, thus eliminating costly work stappages. Normally done with Se-75 sources.
- Digital Radiography: Digital radiographyis a form of Gamma-ray or X-ray imaging, where digital X-ray sensors are used instead of traditional photographic film. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also less radiation can be used to produce an image of similar contrast to conventional radiography. Instead of conventional film, digital radiography uses a digital image capture device. This gives advantages of elimination of costly film processing steps and a wider dynamic range, which makes it more forgiving for over- and under-exposure. The image software also gives the ability to apply special image processing techniques that enhance overall display of the image.
NDT - Ultrasonic Testing (UT)
Productivity and quality are the buzz words in quality control and in-service inspection and ultrasonic non-destructive testing (NDT) is certainly the answer. Ultrasonic technology is used to measure wall thickness, detect hidden cracks and other anomalies affecting structural integrity.
During the last 20 years, the wide use of ultrasonics for the non-destructive testing of construction components and material has increased the importance of the method for industrial quality control. In ultrasonic testing, high frequency sound waves ranging from 10MHz-1MHz are transmitted into a material to detect surface and subsurface discontinuities.
- Conventional Ultrasonic Testing (UT): Conventional Ultrasonic Testing equipment works with the principle of sending a pulsed beam of high-ultrasound from a handheld transducer, which is placed upon the surface of the object being tested. This wave will be disturbed and then partially returned from internal imperfections or from the back of the material wall. The return sound is displayed upon the screen of the ultrasonic equipment, presenting the amplitude of the pulse and the duration taken for return to the transducer. By measuring this sound a skilled operator can identify location and orientation of imperfections respective the wall thickness of the material. Acceptance criteria define whether or not the indication is acceptable or rejectable.
- Phased Array Ultrasonic Testing (PA): Phased array ultrasonics uses multiple ultrasonic elements and electronic time delays to create beams by constructive and destructive interference. The technique typically incorporates a multi-element array transducer that generates a sweeping beam that can examine a part from various angles and focal points to create a detailed picture of internal conditions. Phased-array technology offers the capability for high-speed electronic scanning without moving parts and greater flexibility for inspecting complex geometries. Moreover, the beams can be steered, scanned, and focussed electronically, and these methods offer significant technical advantages over conventional ultrasonics, and other NDT methods.
- Time of Flight Diffraction Technique (TOFD): Time of Flight Diffraction inspection employes two longitudianl wave (L-wave) angle beam tansducers arranged symmetrically opposite facing each other, straddling the weld or base material under test. One probe acts like transmitter of ultrasonic energy while the other probe receives the ultrasound energy. The transducer, pulser, and amplifier characteristics are selected to generate as broad distribution of energy as possible over the material under test providing full weld coverage. A single-axis scan along the weld with an encoder records the position of the weld and enables the display of digital images in real time.
- Ultrasonic Wall Thickness Testing (WT): One of the most basic ultrasonic methods applied is using a zero degree dual transducer probe to send an ultrasonic beam into a component and receiving the ultrasound energy bounced back from the far wall of the component. Thus a pulse-echo technique, where the time travelled from the exitation pulse to the first echo signal is used to determine the material thickness. These tests are normally done with probe frequencies ranging from 5 to 10 MHz and can measure thicknesses from 0.7mm to 200mm, and in temperature ranges of -5 ºC to 500 ºC.
- Guided Wave Ultrasonics (GUL): The Wavemaker Pipe Screening System uses low frequency guided ultrasonic waves that propagate along the pipe wall and is designed for rapid screening of long lenghts of pipe to detect external or internal corrosion as well as axial and circumferential cracking. This is composed of three primary components, the transducer ring, the Wavemaker G3 instrument, and the controlling computer. Traditionally the pipes and tubes in boiler components were tested with normal spot ultrasonics using zero degree transducers where erosion, corrosion and abrasion was evident or visually detected, and often limited inspections were done due to access constraints. With the combination of the Wavemaker G3 System and the improved Claw system provides a guided waves inspection solution to the boiler tubes, offering a 100% coverage over the inspection range that can be up to several tens of meters.
NDT - Magnetic Particle Testing (MT)
Magnetic particle testing is a widely established non destructive method for the detection of surface breaking flaws as well as sub-surface flaws with depths of 2-3mm. The method is accomplished by inducing a magnetic field in ferromagnetic materials. The surface is coated with a white contrast paint and over this paint iron particles suspended in liquid are applied. Surface and near surface flaws produce magnetic poles and iron particles are attracted and concentrated, producing a visible indication of the defects on the surface of the material. The length of an indication can be accurately determined, but the depth cannot be determined with this method.
NDT - Liquid Penetrant Testing (PT)
Liquid penetrant testing is a traditional non-destructive method for inspection of surface breaking flaws such as cracks and porosity in test objects with non-porous surfaces. The tested surface is cleaned and coated with a penetrant solution either a visible or fluorescent dye that is drawn into the discontinuity by capillary action. The excess solution is removed from the surface, but the penetrant remains in the surface breaking flaws. A white developer is then applied to draw the penetrant out of the defects and shows a contrast image. After the evaluation of the indications the surface is cleaned.
Liquid penetrant testing can be used on relatively dirty surfaces, but the sensitivity is decreased, but a fluorescent penetrant can also be used that gives increased sensitivity. The length of an indication can be accurately determined, but the depth cannot be determined with this method.
NDT - Hardness Testing (HT)
Mobile hardness testing is on the advance, as it represents a quick, economical and dependable way to measure hardness. Hardness testing is understood as the resistance of a material against the vertical penetration of a body by a material of greater hardness. The hardness of a material is determined by forcing an indenter into the surface of the material under load and then measuring the indentation size, or the backward bounce speed and distance of the plunger applied. There are three principal standard test methods for expressing the relationship between hardness and the size of the impression, these being Brinell, Vickers, and Rockwell.
|NDT - Positive Material Identification (PMI)|
The portable scientific analyzers use as principle of operation XRF sepctrometry (X-Ray Fluorescence), and are engineered for quick aqualitative and quantitative analysis of alloys, geological and enviromental samples. This method is non destructive and fast, allows the analysis of many elements simultaneously, and is applied for a range of concentrations.
Analyzers rapidly determine those elements present in the sample and their relative concentrations - in other words, the elemental chemistry of the sample. For samples with known ranges of chemical composition, such as common grades of metal alloys, the analyzer also identifies most sample types by name, typically in seconds.
|NDT - Field Metallurgical Replication (Replicas)|
Replication is used as a tool for evaluating microstructures and other surface features in lieu of laboratory evaluations. The procedure is performed by trained technicians using portable polishing equipment following procedures for the preparation of metallographic samples. Producing a replica requires abrasive preparation using succesively finer grits, followed by a final diamond-impregnated cloth polish. The work is done with portable polishing equipment and smaller diameter grinding and polishing disks that prepare the surface for an acid etch. A thin plastic film is then used to replicate the etched surface and this is then viewed under a microscope and provides the metallurgical engineer a two-dimensional view of the microstructure, similar to that observed in a labotory metallographic specimen. Features such as grain size and orientation, voids and cracks are easily identifiable.