Non-destructive testing (NDT) is a method used to inspect, test, or evaluate materials and structures without causing any damage to them. It involves various techniques that can identify defects, irregularities, and weaknesses in a non-invasive manner, ensuring the integrity and reliability of the inspected components. 

        Magnetic particle inspection (MPI) is a non-destructive testing method used to detect invisible surface and near-surface defects up to 2 mm deep. The purpose is to inspect ferromagnetic materials such as steel and iron.

        This inspection is crucial in industries such as manufacturing, construction, and infrastructure where these materials are commonly used. It is used for quality control purposes to ensure the integrity and safety of critical components, especially in areas prone to high stress or fatigue. 

        The MPI process relies on the principle of magnetic fields and the application of ferromagnetic particles to identify any defects, including cracks, voids, seams, and discontinuities. By magnetizing the material under inspection, the ferromagnetic particles are attracted towards the defects, forming visible indications, or "magnetic particle indications."

        These indications can reveal the presence, size, shape, and location of the defects. Magnetic particle inspection is highly sensitive and can detect very small cracks with an opening width as small as 0.001 mm and a depth of 0.01 mm or more. This makes it suitable for identifying even the tiniest defects in various materials. 

        Wet Method: In this method, a magnetic field is applied to the material being inspected using a magnetic yoke, electromagnetic coil, or permanent magnet. After magnetization, a suspension of iron particles in a liquid carrier is applied to the surface. The particles are attracted to and accumulate at any surface or near-surface defects, making them visible for inspection.

        The excess liquid is removed, and the detected defects can be evaluated and documented. 

        Dry Method: This method involves applying dry iron particles to the magnetized surface using a powder blower or dusting. The particles adhere to the magnetic field leakages caused by defects, making them visible.

        The excess particles are removed, and the detected indications can be examined and assessed. 

        Visual testing is a non-destructive testing method used to examine the surface or appearance of an object for defects. It is typically performed with the naked eye or with the aid of magnifying glasses, also known as magnifiers. Regular visual testing is done with magnifiers that have a typical magnification range of up to 7x. However, in cases where the defect is not easily detectable or if a more detailed examination is required, magnifiers with higher magnification, up to 20x, may be utilized.  

        When preparing the material for visual testing, it is necessary to remove any rust, scale, dirt, paint, oil, metal spray, or other impurities using appropriate cleaning methods. By ensuring the material surface is clean and free from impurities, the inspector can inspect the material accurately, identify any defects or damage, and make reliable judgments based on the visual inspection results.