What are the advantages and limitations of PT compared to other NDT methods for welds?

Non-Destructive Testing (NDT) methods are used to assess the integrity and quality of welds without causing any damage to the test piece. One such method is Penetrant Testing (PT), which involves applying a liquid penetrant to the weld surface and using contrasting dyes to detect surface-breaking defects. When compared to other NDT methods of weld inspection, PT has its own set of advantages and limitations.

PT is usually used for defects that have a path to the surface, and this is a major limitation and does not reveal the defects that exist within the part and below the surface with a small distance.

Advantages of PT, can effectively detect surface-breaking defects like cracks, porosity, and lack of fusion, which may not be easily detected by other methods like Ultrasonic Testing UT. Can provide detailed information about the size and location of such defects. PT is generally less expensive than techniques like radiographic testing or ultrasonic inspection, making it a more economical option, especially for smaller companies or projects with budget constraints. PT equipment is generally portable and easy to use, making it suitable for on-site inspections. PT can be applied to a wide range of materials, including metals, plastics, ceramics & composites, allowing for versatility.

PT is often performed prior to RT - both RT and PT are considered complimentary NDT methods... Basically, PT is just an enhanced visual inspection. For any NDT method, test specimen or material process familiarity is very important to recognize potential defect types likely to be encountered.

It's pretty simple really..... As already said.... PT is a surface inspection(with capability of detecting defects up to 3mm deep) and is predominantly used on non ferritic materials, UT on the other hand can be used on any material and detects sub surface defects but can also detect surface defects depending on the item of inspection. Austenitic materials such as stainless steel is alot more complex due too the grain structure and acoustic impedance.

PT is a cheap NDT techniques to use but limited to surface breaking and requires more preparation for the component to be inspected.

Considering welding, PT have the most favourite advantage that, the minimum training required based on procedure and work instructions under supervision of level II & level III.... the person performing the test can be a welder himself or any other person who receives training as mentioned above. With the awareness of the expected defects in the weld, one can perform the test easily... of course, this is for internal/intermediate stages. The final PT shall be done by the authorised level II person. PT (and also MPT) is an advanced version of VT.... the surface defects which are not visible easily, are made visible by use of PT & MPT.. so, use of these NDT methods is a good support to the production team. Other advantages are also important.

In case of welds, the most crucial part for PT is the 'surface preparation'. The limitation regarding heavy background is prominent if surface is rough or as welded. Lot of care is required for excess penetrant removal. There shall be minimal background but at the same time the penetrant trapped in defects needs to be protected and here the skills of the person performing PT is more important. The other limitation is the temperature of the weld surface. PT shall be performed at the specified temperature so the operator shall wait till the temperature is under range. This kills lot of production time. Improper cleaning after completion of test is also a limitation that have many reasons apart from workmanship.

Correction - penetrant is not typically used on "coated" material. Coatings can mask or hide discontinuities at the material's surface.

Question why don't want to do PT on porous material? Correction : Coated material means they hide the discontinuities we need to do PT prior to the coating and painting

PT : Need to be clean of any dirty area or coated area ( e.j : Oxide, Corrosión , Moisture, anodize , Paint , etc etc) , sometimes the technician need to do a extra clean

For wedding, I think MT will be more supportive instead of PT. The limitation of weld surface temperature can be tackled by use of 'Hot MPI' technique where special powder is used which withstands the elevated temperature. Also, the time to perform MT is less than time to perform PT...

PT is often used prior to RT - they often considered complimentary NDT methods.. Also, it needs to be understood that crack detection (or other lamillar type defects) has low PoD in RT due to orientation sensitivity - similar to UT - both UT and RT are volumetric methods - they can readily detect a loss of material volume to some degree, but separation of materials with no loss of volume can present challenges if orientation of penetrating signal(s) is not favorable.

Corrections - PT cannot detect internal defects and typically does require trained personnel ans sometimes special equipment.

I don't see much similarity between UT and PT. Conventional UT is not normally used for detecting surface breaking discontinuities. Conventional UT is best deployed searching for sub-surface discontinuities on thicker section carbon steel butt welds, PT is usually applied on stainless steel and non-ferrous materials and is limited to surface breaking discontinuities. I agree UT is more complex, but metre by metre won't be any slower than properly executed PT. Finally, UT does require more training and much more on the job training and experience to achieve competency but that does not mean PT does not. In the wrong hands PT is just a way of making a mess!

This is like comparing apples and oranges. Both techniques have thier own place and merits. Quite simply, PT is widely accepted as an visual inspection technqiuqe limited to 'surface' Only. Whereas UT is considered as 'Volumetric' with ability to assess components for presence of internal flaws or undesirable defects outside of accetble tolerances. Both technqiues rely upon the competency and skill of the practitioner, but for me the biggest difference in this space is UT capability and superiority it offers in terms of being able to test far more complex geometeries than its PT counterpart.

Same as mentioned above for RT. PT cannot detect internal defects and does require trained personnel and sometimes special equipment.

RT cannot size defects in the vertical plane, while AUT can , more capabilities+better detection= Safer welds and at the end of the day the integrity of the weld is what matters...above cost, complexity,etc.. Its a win win situation that it also eliminates the danger to human life through radiation exposure that Rt carries.

Correction : in that PT did not find internal defects it is finding surface and sub surface (like hollow shaft type) defects