Any welded metalware used in the construction of buildings and structures are subject to mandatory acceptance tests to confirm that the quality of elements meets the existing standards and technical documentation. As part of the entrance control, specialists of the SKEP construction laboratory carry out flaw detection of welded joints – visual and instrumental examination of seams aimed at identifying external and internal defects.
The quality of welded joints is the key to reliable operation of structures
A significant part of construction metalware is produced by arc, mechanized or automated welding. Welds have large-span frames and various structural elements – trusses, crane beams, columns, etc. Welding is used for installation of cold and hot water supply heating pipes.
The tightness of low, medium and high pressure pipelines, the load-bearing capacity of structures and the operational life of buildings depend on the quality of the welded joint.
To assess the reliability and timely detection of violations of the assembly (welding) technology, SKEP specialists use effective methods of flaw detection (nondestructive testing), selected after a visual inspection of the seams. What types of defects can be detected during the examination?
Defects of welded joints
The most common external defects are detected during visual inspection of metal structures, which is carried out using a magnifying glass, lighting devices and measuring tools (templates, rulers, etc.). the Main (visual) method of flaw detection of welded joints allows to identify:
- cold laping and overlap,
- burnthrough and surface oxidation,
- undercuts and gas pockets,
- cracks,
- violations of the shape and size of the seam,
- unfilled craters.
The causes of surface defects in welded joints are often associated with violations of technological conditions, thermal phenomena, poor preparation of the welded parts (cleaning, removal of contamination), as well as the impact of various external factors (weather conditions, etc.).
Weld flaw detection, performed using non-destructive testing methods (magnetic, capillary, ultrasonic, radiographic, etc.), allows you to determine the presence, location and nature of hidden defects, many of which are the cause of structural failure.
In the course of an instrumental examination of the joints, which complements the visual inspection, flaw detectors detect:
- cold and hot cracks,
- slag inclusions,
- tungsten and oxide inclusions,
- pores (internal cavities).
Weld flaw detection – non-destructive testing
Methods of non-destructive testing of welded joints belong to the category of additional works and are applied after the main visual and instrumental inspection. If defects are detected at the visual and instrumental inspection stage, there is no need to use x-ray equipment, ultrasonic flaw detectors, penetrators, and other tools and devices (until the detected external defects are eliminated).
Non-destructive methods of flaw detection used by specialists of the SKEP construction laboratory include:
- acoustic (ultrasonic) monitoring,
- x-ray flaw detection,
- eddy current control of welded joints,
- magnetic and capillary methods.
Liquid penetrant testing
The smallest pores and cracks (thousandths of a millimeter), which are difficult to detect even with a tenfold magnification portable magnifier, are detected using indicator contrast agents (penetrants) that penetrate the defective layers of compounds under the action of capillary pressure.
This method of flaw detection of welds will allow you to determine any external defects that have an outlet to the surface. When interacting with the developer, the dye penetrant is “pushed” out of the crack, forming a clear pattern (indicator trace) in the form of lines (cracks) and/or points (pores).
Ultrasonic, radiation and magnetic flaw detection
The unique ability of ultrasonic waves to distort when “meeting” with various inhomogeneities and cracks is used to detect hidden defects of welded joints by the ultrasonic testing method. Any deviations that are in the “path” of the wave are detected by a special sensor and decoded by an experienced expert who uses the method of ultrasonic flaw detection of welds.
Defective sections of the welded joint are easily detected by penetrating x-rays or gamma rays, the intensity of which depends on the density of the metal. The result is displayed (illuminated) on an x-ray film installed together with two amplifying screens in a light-tight cassette on the opposite side of the examined seam (opposite the x-ray tube).
Magnetic flaw detection is an equally popular method for measuring the quality of welds, based on registering the magnetic flux spread through the metal product in various ways. Defects that have a lower magnetic permeability “displace” magnetic force lines (magnetic scattering flux), whose distortions are detected using a ferromagnetic tape or magnetic powder.
You can order flaw detection of welded joints right now by calling the SKEP company.
