Breaking News

The Basics of Liquid Penetrant Inspection

Liquid Penetrant Inspection 3Liquid penetrant inspection (LPI), also known as dye penetrant inspection (DPI) or simply penetrant inspection (PI), is an inspection method for locating surface breaking defects in non- porous materials (like metals, ceramics, plastics, etc). It is an inexpensive and widely applied inspection method.

The penetrant can also be applied on ferrous and non- ferrous materials. However, in case of ferrous materials, magnetic- particle inspection (MPI) is often used. MPI is a testing method to detect surface (even slightly sub- surface) discontinuities in ferrous substances (like nickel, iron, cobalt and some of their alloys). LPI detects forging, casting and welding surface defects, such as surface porosity, hairline cracks, fatigue cracks on in- service components, and leaks in new products.

Steps of LPI

LPI works on the principle of capillary action, the ability of a liquid to flow in narrow spaces without the influences of any external forces (like gravity). The inspection is performed under white or fluorescent light, based on the type of dye used. Let’s look at the steps involved in LPI:Liquid Penetrant Inspection 2

Cleaning the surface– The test surface is cleaned to remove any paint, grease, oil or dirt that may prevent the penetrant from entering the cracks. The surface can be cleaned in various ways, including vapour degreasing (in which the solvents dissolve the contaminants and leave them dripping off the surface), alkaline cleaning, media blasting, or cleaning with solvents. The aim of the cleaning is to obtain a clean surface where the defects (if any) will be dry, open to the surface and free of contamination.

Penetrant application– The next step is the application of the penetrant on the surface. The penetrant may be applied by brushing, dipping, or spraying. The penetrant is allowed a standing time, known as ‘dwell time’, in which it enters into the flaws. The ‘dwell time’ may range from 5 – 30 minutes, depending on the material being tested, the penetrant applied and the size of flaws being detected. Note- smaller flaws need longer ‘dwell time’.

Liquid Penetrant Inspection 1

Removal of excess penetrant– The excess penetrant left on the surface after the ‘dwell time’ is removed from the surface. The removal method depends on the type of penetrant used. Some of the common removal methods are solvent- removable, water- washable, hydrophilic post – emulsifiable, and lipophilic post-emulsifiable. If the excess penetrant is not completely removed, it can cause false indications.

Developer application– After the excess penetrant is removed, a white developer is applied. The purpose of the developer is to draw the penetrant out of the flaw so that a visible indication may be seen. This process is known as ‘bleed out’. Developers are of several types, including dry powder, water soluble and water suspendable. The type of developer one uses depends on the penetrant type and the inspection conditions. Once the defect is detected, inferring the results and categorising it may need training and experience.

Post inspection– The test surface is cleaned after the inspection, especially if post- coating process is scheduled.

If you are an inhabitant of Edmonton and own an industry where you want to perform an inspection, you needn’t worry. There are many good companies that offer excellent inspection services, like magnetic particle inspection, liquid penetrant inspection in Edmonton.

Nicola is a renowned author. She has written many articles on industry management. She is herself a proud owner of a prestigious industry in Edmonton and has availed the services of inspection services and got amazing and satisfying results. In this article she writes about inspection services.

Liquid penetrant inspection (LPI), also known as dye penetrant inspection (DPI) or simply penetrant inspection (PI), is an inspection method for locating surface breaking defects in non- porous materials (like metals, ceramics, plastics, etc). It is an inexpensive and widely applied inspection method. The penetrant can also be applied on ferrous and non- ferrous materials. However, in case of ferrous materials, magnetic- particle inspection (MPI) is often used. MPI is a testing method to detect surface (even slightly sub- surface) discontinuities in ferrous substances (like nickel, iron, cobalt and some of their alloys). LPI detects forging, casting and welding surface defects, such as surface porosity, hairline cracks, fatigue cracks on in- service components, and leaks in new products.

Steps of LPI

LPI works on the principle of capillary action, the ability of a liquid to flow in narrow spaces without the influences of any external forces (like gravity). The inspection is performed under white or fluorescent light, based on the type of dye used. Let’s look at the steps involved in LPI:

Cleaning the surface– The test surface is cleaned to remove any paint, grease, oil or dirt that may prevent the penetrant from entering the cracks. The surface can be cleaned in various ways, including vapour degreasing (in which the solvents dissolve the contaminants and leave them dripping off the surface), alkaline cleaning, media blasting, or cleaning with solvents. The aim of the cleaning is to obtain a clean surface where the defects (if any) will be dry, open to the surface and free of contamination.

Penetrant application– The next step is the application of the penetrant on the surface. The penetrant may be applied by brushing, dipping, or spraying. The penetrant is allowed a standing time, known as ‘dwell time’, in which it enters into the flaws. The ‘dwell time’ may range from 5 – 30 minutes, depending on the material being tested, the penetrant applied and the size of flaws being detected. Note- smaller flaws need longer ‘dwell time’.

Removal of excess penetrant– The excess penetrant left on the surface after the ‘dwell time’ is removed from the surface. The removal method depends on the type of penetrant used. Some of the common removal methods are solvent- removable, water- washable, hydrophilic post – emulsifiable, and lipophilic post-emulsifiable. If the excess penetrant is not completely removed, it can cause false indications.

Developer application– After the excess penetrant is removed, a white developer is applied. The purpose of the developer is to draw the penetrant out of the flaw so that a visible indication may be seen. This process is known as ‘bleed out’. Developers are of several types, including dry powder, water soluble and water suspendable. The type of developer one uses depends on the penetrant type and the inspection conditions. Once the defect is detected, inferring the results and categorising it may need training and experience.

Post inspection– The test surface is cleaned after the inspection, especially if post- coating process is scheduled.

If you are an inhabitant of Edmonton and own an industry where you want to perform an inspection, you needn’t worry. There are many good companies that offer excellent inspection services, like magnetic particle inspection, liquid penetrant inspection in Edmonton.

Nicola is a renowned author. She has written many articles on industry management. She is herself a proud owner of a prestigious industry in Edmonton and has availed the services of inspection services and got amazing and satisfying results. In this article she writes about inspection services.

If you enjoyed this article, Get email updates (It’s Free)