Stainless steel is widely used in various industries thanks to a high degree of corrosion resistance. Petersburg Plant of Precision Alloys releases a range of corrosion-resistant steels and alloys, including:
In addition, analogues of foreign heat-resistant and heat-resistant materials KhN78T and KhN53BMTYU, which in characteristics is similar to the well-known foreign alloy NN 718, were developed and successfully launched into production at the enterprise.
However, even stainless steel can undergo various destruction processes if its protective passive layer is damaged or insufficiently formed. In this connection it is important to have an effective method of detecting defects on the surface of highly alloyed steel in order to timely prevent corrosion destruction.
Recently a research group of German scientists developed an innovative express test for detecting defects in the passive layer of stainless steel. This method, named KorroPad, is a simple and effective way to assess the state of the material surface.
The main idea of protecting stainless steel from corrosion is formation on the surface of a thin layer (only a few atomic layers thick) of chromium oxide called the passive layer. If this layer is damaged, undesirable corrosion reactions may arise that seriously damage the material. KorroPad makes it possible to quickly detect such violations, giving the opportunity to timely take measures to eliminate them.
The method is based on using test pads with an indicator solution containing an activator that is in a gel-like state thanks to a special binder. The pad imitates a moist film on the surface of the object under test and maintains a certain corrosion system. Presence of iron ions colors KorroPad blue, making it possible to detect an incomplete passive layer. At present this method is suitable for most common stainless alloys, but for low-alloy steels the test must be adapted.
To conduct the test three pads the size of a two-ruble coin are required. These pads are pressed to the cleaned stainless steel surface and left on it for 15 minutes. Then they are removed with a spatula. If the steel’s passive protective layer is damaged, the indicator on the pads reacts with iron ions in the material, and blue dots appear on the surface. Each dot indicates places where the protective layer did not form properly.
The KorroPad method can be applied in the temperature range from +5 to +50°C, but best results are achieved at +20±5°C. Test time is usually 15 minutes but may be changed if necessary.
Evaluating KorroPad test results is very simple. If there are no signs of corrosion on the pads, one can conclude that the passive layer on the stainless steel surface is formed optimally and the material has good corrosion resistance.
KorroPad is a comparative methodology that gives an idea of the alloy’s surface characteristics for practical use. If necessary its “good/bad” evaluation criterion can be adapted to specific production tasks.
The KorroPad method ensures fast, effective detection of defects on the stainless steel surface, making it possible to promptly take measures to eliminate them. Thanks to simplicity of application and result evaluation, even non-professionals can use this test. In addition, during testing no residues or traces remain on the steel or alloy surface, making it possible to apply this methodology at any stage of working with stainless alloys.
The KorroPad express test for stainless steel resistance to pitting corrosion is an effective, reliable method of assessing material corrosion resistance. Its simplicity and speed of conduct make it an ideal tool for quality control of incoming and outgoing products, as well as for optimizing surface treatment processes.
