Liquid penetrant testing (PT), often called dye penetrant testing or, with fluorescent dyes, fluorescent penetrant inspection, finds cracks and other flaws that are open to the surface. A penetrant is drawn into the flaw, the excess is removed from the surface, and a developer draws the penetrant back out to show where the flaw is.
- Finds
- Quench, grinding and fatigue cracks; overload and impact fractures; porosity, laps, seams, pinholes in welds, lack of fusion
- Typical use
- Castings, forgings, weldments, aerospace components, non-magnetic material
What dye penetrant testing finds
PT is the least expensive NDT method, and it works on ferrous and non-ferrous material alike. It finds flaws that are open to the surface, including:
- Fatigue, quench and grinding cracks
- Overload and impact fractures
- Porosity and pinholes in welds and castings
- Laps, seams and surface lack of fusion
A flaw that is closed at the surface, smeared over by machining, or filled with paint, oxide or dirt will not take up penetrant. Surface preparation matters as much as the penetrant itself, and it is written into the procedure.
Visible or fluorescent penetrant?
Visible (red dye) penetrant is portable and needs only white light, which suits field work and welds. Fluorescent penetrant is examined under ultraviolet light in a darkened area and is more sensitive, which is why aerospace specifications usually call for it. The penetrant type, sensitivity level and removal method are set by the procedure and the specification you work to.
Penetrant or magnetic particle?
On carbon and low-alloy steel, magnetic particle testing is usually faster and can find flaws just below the surface that penetrant cannot. On stainless steel, aluminum, titanium, nickel alloys and other nonmagnetic material, penetrant is the standard choice.
Where it’s used
- Aerospace components, where fluorescent penetrant is the norm
- Castings, forgings and machined parts in manufacturing
- Stainless steel and aluminum welds
- Nuclear and power generation components
- Automotive parts, amusement rides and lifting devices
Codes and standards
The test method standard says how to perform the test. The construction code or customer specification says which indications are rejectable. Common documents include:
- ASTM E1417/E1417M, the standard practice for liquid penetrant testing, widely used in aerospace and defense work
- ASTM E165/E165M, the practice for liquid penetrant testing in general industry
- ASME Boiler and Pressure Vessel Code, Section V, Article 6, with acceptance in the referencing section or in ASME B31.3
- AWS D1.1 and the other AWS structural welding codes
- SAE AMS 2644, which qualifies the penetrant materials themselves
Who does the work
Every Midgard technician who performs liquid penetrant testing holds current certification in that method, issued under a written practice. For most industrial work the written practice follows ASNT’s SNT-TC-1A; for aerospace and defense work it follows NAS410. A Responsible Level III oversees the program: approving procedures and technique sheets, examining and certifying technicians, and answering the technical questions that come up on the job.
If your contract calls for a different scheme, such as ANSI/ASNT CP-189 or NAVSEA requirements, tell us when you ask for a quote.
Training in liquid penetrant testing
Midgard also trains in liquid penetrant testing, along with all the other major methods. Instruction is given at Level I, II and III by certified Level III instructors, to SNT-TC-1A, CP-189, NAS410, NAVSEA or whichever code you certify to, with general, specific and practical examinations at your facility or ours. It suits new hires working toward first certification as well as technicians due for re-examination. See training and certification, or ask about a class.
Common questions
How long does a dye penetrant test take?
Most of the time is waiting. The penetrant has to stay on the surface for a minimum dwell time, and the developer needs time before the indications are read. The procedure sets both for the material and temperature, typically in the range of several minutes to half an hour each, plus cleaning before and after.
What are the advantages and disadvantages of penetrant testing?
It is inexpensive, portable, works on almost any non-porous material and examines large or complex surfaces in one pass. On the other hand, it finds only flaws open to the surface, needs a clean surface and careful removal of excess penetrant, does not work on porous material, and the chemicals have to be cleaned off afterward.
Where do dye penetrant acceptance criteria come from?
Not from the test method. ASTM E1417, ASTM E165 and ASME Section V describe how to do the test. Acceptance criteria come from the governing code or specification, such as ASME Section VIII, ASME B31.3 or AWS D1.1, and we evaluate indications against the document that applies to your part.
Can penetrant testing be used on stainless steel and aluminum?
Yes. That is one of its main uses, since those materials cannot be tested with magnetic particle. For nickel alloys, austenitic stainless steel and titanium, the penetrant materials must be controlled for sulfur and halogen content, and the procedure says which materials to use.
Tell us the material, the parts or welds, the quantity and the specification, and whether you need visible or fluorescent penetrant. Call 1-844-MIDGARD, email contact@midgardscientific.com, or use the contact page.