Penetrating liquid test (PT) what is it
Penetrating liquid test (Penetrant Testing یا PT) One of the most used methods Non-destructive tests (NDT) It is used to identify discontinuities and surface defects in parts and equipment. In this method, a liquid with high penetrability is applied to the surface of the part to penetrate cracks, pores, laps, seams or other discontinuities open to the surface..
After removing the excess penetrant from the surface, using the detector (Developer), the remaining liquid within the discontinuities returns to the surface and appears as a visible signature..
One of the most important advantages of liquid penetrant inspection is that, unlike many other methods, it does not require complex and expensive equipment and can be used to inspect a wide variety of non-porous metal and non-metal parts..
Application of PT test in technical inspectionPenetrating liquid test is used in various industries such as oil, gas and petrochemical, power plants, aerospace, automotive, foundry, industrial equipment manufacturing, pressure vessels and marine industries..
Application of PT test in technical inspectionPenetrating liquid test is used in various industries such as oil, gas and petrochemical, power plants, aerospace, automotive, foundry, industrial equipment manufacturing, pressure vessels and marine industries..
This method can be used to inspect parts such as welds, joints, flanges, machined parts, cast and forged parts, and also to identify surface cracks in equipment..
especially in Welding inspection (Welding Inspection)PT test can be used to identify defects such as surface cracks, lack of fusion open to the surface, open porosity and some surface discontinuities..
Penetrating liquid test steps (PT):
The penetrant inspection process consists of several main steps. The correct and controlled implementation of each step is very important; Because the quality of the final PT result directly depends on surface preparation, penetration time, cleaning method and observation conditions:
۱. Surface cleaning (Cleaning)
The first and one of the most important steps of penetrant testing is the complete cleaning of the tested surface.
The first and one of the most important steps of penetrant testing is the complete cleaning of the tested surface.
The surface of the part must be cleaned of any oil, grease, dust, rust, paint, oxide scale, water, chemicals and other contaminants that can prevent the penetration of the penetrating liquid..
The presence of contamination on the surface may block the opening of a crack and prevent penetrating fluid from entering the discontinuity. As a result, a true defect may not be detected or its signal may be weaker than the actual value.
Therefore, cleaning is not just a preliminary step; Rather, it is one of the main factors of PT test accuracy and reliability.
۲. Penetrating fluid application (Applying Penetrant)
After surface preparation, penetrating fluid (Penetrant) It is applied on the surface of the part in a suitable way.
Penetrating liquid due to wetting properties (Wetting) and capillary forces (Capillary Action) It can enter discontinuities that are open to the surface.
At this stage, it must be ensured that the entire inspected area is uniformly covered with the penetrating liquid.
The penetrant used can be colored or visible (Visible Dye Penetrant) or fluorescent (Fluorescent Penetrant) be.
After surface preparation, penetrating fluid (Penetrant) It is applied on the surface of the part in a suitable way.
Penetrating liquid due to wetting properties (Wetting) and capillary forces (Capillary Action) It can enter discontinuities that are open to the surface.
At this stage, it must be ensured that the entire inspected area is uniformly covered with the penetrating liquid.
The penetrant used can be colored or visible (Visible Dye Penetrant) or fluorescent (Fluorescent Penetrant) be.
۳. Time to stop or penetrate (Dwell Time)
After applying the penetrating liquid, a certain period of time should be considered for its penetration into the discontinuities. This time is known as dwell time.
After applying the penetrating liquid, a certain period of time should be considered for its penetration into the discontinuities. This time is known as dwell time.
Penetration time depends on factors such as the type of penetrating liquid, the material and condition of the surface of the part, the type and possible size of the discontinuity, and the implementation instructions of the test..
If the penetration time is too short, the penetrating fluid may not have enough time to penetrate very small defects. On the other hand, an unreasonable increase in penetration time does not necessarily increase the accuracy of the test.
If the penetration time is too short, the penetrating fluid may not have enough time to penetrate very small defects. On the other hand, an unreasonable increase in penetration time does not necessarily increase the accuracy of the test.
For this reason, the stopping time should be determined according to the instructions of the manufacturer of the consumables and the implementation method or the relevant standard.
۴. Wipe off excess penetrant (Excess Penetrant Removal)
At the end of the penetration time, the excess penetrating liquid that remains on the surface of the part must be removed in a suitable way.The purpose of this step is to remove the penetrant on the surface, while leaving the penetrant trapped inside the discontinuities..
This stage is one of the most sensitive parts of the PT test.If the surface is cleaned too much, the penetrant may also escape through the discontinuity and the true indication of the defect is lost. On the other hand, if the excess penetrant is not properly removed, too much background is created and the possibility of false indication is increased..
۵. Surface drying (Drying)
After removing the excess penetrant, the surface of the part is dried if necessary to provide suitable conditions for the detection step.
Residual moisture on the surface can affect the performance of the detector material and reduce the quality of the sighting of the marks.Method and dry conditions It should also be selected according to the implementation method and the type of penetrating material system.
After removing the excess penetrant, the surface of the part is dried if necessary to provide suitable conditions for the detection step.
Residual moisture on the surface can affect the performance of the detector material and reduce the quality of the sighting of the marks.Method and dry conditions It should also be selected according to the implementation method and the type of penetrating material system.
۶. Apply the detector (Applying Developer)
In this step, the detector or developer is applied to the surface.
The developer acts as an absorbing medium and pulls the penetrant remaining inside the discontinuity towards the surface.. As a result, the defect mark becomes larger and more visible.
The developer acts as an absorbing medium and pulls the penetrant remaining inside the discontinuity towards the surface.. As a result, the defect mark becomes larger and more visible.
In fact, the detector increases contrast and detectability (Detectability) It becomes signs.
Choosing the type of developer and how to apply it can have a significant impact on the quality of the inspection. Depending on the system used, the detector can have different types and its selection should be done according to the requirements of the test method.
۷. View and evaluate results (Inspection & Interpretation)
After applying the developer and passing the appropriate time to form the mark, the surface of the part is observed.In the color penetrating liquid method (Visible Penetrant), the marks are usually seen as a color effect with a suitable contrast to the surface and the inspection is done under visible light conditions..
In fluorescent penetrant method (Fluorescent Penetrant), signs obtained under ultraviolet light (UV-A) are observed. This method usually allows the detection of very small discontinuities and is therefore used in many sensitive applications..
In fluorescent penetrant method (Fluorescent Penetrant), signs obtained under ultraviolet light (UV-A) are observed. This method usually allows the detection of very small discontinuities and is therefore used in many sensitive applications..
During the evaluation, the appearance, shape, length, position and direction of signs are checked and their dimensions are recorded if needed..The important thing is that every symptom does not necessarily mean the presence of a failing defect. Interpretation of the sign must be done by a competent person based on the project acceptance criteria, map, technical specification or relevant standard.
The difference between colored PT and fluorescent PT
In terms of general principles, the inspection procedures with colored and fluorescent penetrants are very similar; But the most important difference is in the system of observing signs.
In the color method, signs are observed with visible light and based on color contrast.
In the color method, signs are observed with visible light and based on color contrast.
But in the fluorescent method, the penetrant has fluorescent compounds, and appropriate ultraviolet light is used in a controlled environment to observe the signs..In general, the fluorescent method can have a higher sensitivity for detecting very subtle discontinuities; However, the choice between colored and fluorescent PT should be made based on the material of the part, the level of sensitivity required, the inspection conditions, the project requirements and the relevant standard..
What defects can be detected by penetrative liquid test?
The PT test is mainly designed to identify open surface discontinuities.
Among the items that can be identified, the following items can be mentioned:
Surface cracks (Surface Cracks)
Cracks caused by fatigue (Fatigue Cracks)
Thermal cracks (Thermal Cracks)
Cracks caused by heat treatment
Lap (Laps)
Surface seams (Seams)
Porosity open to the surface (Surface-connected Porosity)
Some surface discontinuities in welding and cast and forged parts
However, PT is not suitable for detecting internal defects and discontinuities that do not reach the surface. For such cases, methods such as ultrasonic testing are possible (UT), radiography (RT) or other NDT methods are required.
Among the items that can be identified, the following items can be mentioned:
Surface cracks (Surface Cracks)
Cracks caused by fatigue (Fatigue Cracks)
Thermal cracks (Thermal Cracks)
Cracks caused by heat treatment
Lap (Laps)
Surface seams (Seams)
Porosity open to the surface (Surface-connected Porosity)
Some surface discontinuities in welding and cast and forged parts
However, PT is not suitable for detecting internal defects and discontinuities that do not reach the surface. For such cases, methods such as ultrasonic testing are possible (UT), radiography (RT) or other NDT methods are required.
Why is surface preparation so important in the PT test?
One of the important points in penetrant testing is that PT is sensitive to surface conditions.A very rough, porous, or contaminated surface can cause spurious signals, increase background, and make results difficult to interpret..
For example, high surface roughness may trap penetrant in surface depressions and cause symptoms that are not necessarily caused by a true crack or defect..
For this reason, the condition of the surface of the part must be checked before the test, and if necessary, appropriate preparation operations must be performed.
For this reason, the condition of the surface of the part must be checked before the test, and if necessary, appropriate preparation operations must be performed.
Advantages of liquid penetrant testing (PT)
Liquid penetrant testing is one of the popular methods in non-destructive inspection due to the following features:
No damage to the piece
PT test is a non-destructive method and if performed correctly, it will not damage the part.
Ability to identify very small cracks
Especially in fluorescent systems, it is possible to observe small surface discontinuities.
Usability for complex geometries
Unlike some NDT methods, the complex shape of the part does not necessarily preclude PT.
Relatively simple equipment
In many applications, portable systems can be used to perform on-site testing.
Reasonable cost
Compared to many advanced inspection methods, the cost of performing PT is usually lower.
Penetrating liquid test limitations
Despite its many advantages, PT also has limitations.This method can only detect discontinuities that are open to the surface and is not suitable for fully internal defects..Also porous materials or surfaces Too coarse can cause background and false marks.
In addition, in the fluorescent method, ambient light conditions and UV equipment must be provided in a controlled manner to maintain the sensitivity and detection capability of the test..
The role of standards in Penetrating liquid inspection، PT results should not be judged solely by operator observation without specific criteria. The standard and Acceptance Criteria determine that an indication is acceptable, evaluable or rejected.
Standards such as ASME, ASTM, ISO, and related industry standards may have different requirements for surface preparation, consumables, test methods, observation conditions, personnel qualifications, and acceptance criteria..
بنابراین در پروژههای صنعتی، انتخاب روش PT باید با توجه به مشخصات فنی پروژه، استاندارد مرجع، نوع قطعه و سطح حساسیت موردنیاز انجام شود.
The role of standards in Penetrating liquid inspection، PT results should not be judged solely by operator observation without specific criteria. The standard and Acceptance Criteria determine that an indication is acceptable, evaluable or rejected.
Standards such as ASME, ASTM, ISO, and related industry standards may have different requirements for surface preparation, consumables, test methods, observation conditions, personnel qualifications, and acceptance criteria..
بنابراین در پروژههای صنعتی، انتخاب روش PT باید با توجه به مشخصات فنی پروژه، استاندارد مرجع، نوع قطعه و سطح حساسیت موردنیاز انجام شود.
کنترل کیفیت در تست PT برای دستیابی به نتیجه قابل اعتماد، تنها داشتن مایع نافذ و Developer کافی نیست. کیفیت مواد مصرفی، شرایط سطح، زمانهای فرآیند، شرایط نور، تجهیزات مورد استفاده و صلاحیت بازرس همگی باید کنترل شوند.همچنین مواد مصرفی آزمون باید طبق الزامات مربوطه نگهداری و در صورت نیاز کنترل یا بررسی شوند.
در پروژههای حساس، مستندسازی فرآیند و نتایج نیز اهمیت زیادی دارد و گزارش بازرسی میتواند شامل مشخصات قطعه، محدوده بازرسی، روش آزمون، مواد مصرفی، شرایط انجام آزمون، نشانههای مشاهدهشده و نتیجه نهایی باشد.
Penetrating liquid test (PT) روشی ساده اما بسیار حساس برای شناسایی ناپیوستگیهای سطحی است. This test starts from the cleaning stage and continues with the application of penetrating liquid, penetration time, removal of excess liquid, drying, application of developer and finally observation and evaluation of symptoms..
The main difference between the two common Visible Penetrant and Fluorescent Penetrant systems is in the way of observing the signs; So, in the fluorescent method, suitable ultraviolet light is used for detection.
The correct implementation of all steps, compliance with the set times, proper preparation of the surface, control of the observation conditions and interpretation of the results based on the standard and acceptance criteria play a fundamental role in the accuracy and reliability of the penetrative liquid inspection..
For this reason, PT, despite its apparent simplicity, is a specialized process, and the quality of the result will depend as much on the materials and equipment as on the correct execution method and the experience and competence of the inspector..