Weld Inspection & Testing

Liquid Penetrant Testing – Advantages, Disadvantages & Alternatives

by Ishita Kapoor on January 5, 2019

Out of all the non-destructive testing techniques, only a few are suited for every type of application. For instance, on most composite materials, electromagnetic testing techniques don’t work, while computed tomography and X-rays are ideal. Likewise, ultrasounds are adaptable, but require appropriate coupling and direct contact with the surface under test, which is not possible in all cases.

What’s Liquid Penetrant Testing? 

Liquid penetrant testing, also known as dye penetrant inspection (DPI) or liquid penetrant inspection (LPI) is one of the most common and affordable solution and one of the oldest, if compared to non-destructive testing challenges. 

The method leverages capillary action, i.e, the ability of a liquid to flow into narrow spaces without help, even in opposition to, external forces such as gravity—to detect surface-breaking defects.

The excess is removed and a developer is applied after applying the penetrant and letting it dwell for a certain period. From surface-breaking defects, the developer draws the penetrant where it’s seeped, revealing their presence.

Advantages of LPI

Liquid penetrant testing has the following advantages:

  • Works on complicated geometric shapes
  • LPI materials are compact
  • Sensitive to small surface interruptions
  • Few material limitations such as—works on non-metallic, metallic, non-magnetic, magnetic, non-conductive and conductive materials
  • Liquid penetrant testing materials are individually very cost-effective
  • Visual, real-world results

Disadvantages of LPI

Liquid penetrant testing has the following disadvantages:

  • Extensive, time-taking pre-cleaning critical—surface contaminants can mask defects
  • Sensitive to surface-breaking defects only
  • Direct connection to the surface under test necessary
  • Works on relatively non-porous surface materials only
  • No depth sizing
  • Multi-process testing procedure
  • Time-taking; post-cleaning also necessary
  • No recordable data handy for progress monitoring
  • User dependent
  • Environmental concerns—may require disposing of chemicals and expensive handling

The biggest disadvantage is that despite lower costs and over time (cheaper materials, less training), Liquid penetrant testing is more than a screening tool; one can measure their length and locate defects, but using this method, it’s impossible to monitor the advancement of defects or determine the severity of its depth. It relegates the method to a pass/fail evaluation, that leads to discarding healthy parts and retaining unhealthy parts—which can both prove expensive.

Hence, in totality, despite the instant captivation of this cost-effective solution, it possesses various downsides that must be looked at before dismissing more progressive and more expensive inspection solutions, whether you contract inspections or perform them on your own.

Alternatives to Liquid Penetrant Testing

Eddy Current Array (ECA)

This offshoot of ECT enhances on the technology using multiplexed arrays of coils that are displayed in rows (instead of one or two coils), allowing to cover a larger area in a single scan pass. Below are the advantages of ECA:

  • Eddy current array probes offer better data than manual raster scans; the larger ECA probes lowers operator dependence
  • Making defect progress monitoring possible, data can be recorded.
  • Wider coverage significantly results in faster scans
  • The simpler ECA scan patterns makes analysis easier, quicker and accurate
  • ECA offers superior detection abilities, and correct defect positioning as the inspection data can be encoded, and—perhaps—sizing.

About IRC Engineering Pvt. Ltd.

IRC is one of the fastest growing Testing and Inspection company in India. We at IRC provide Liquid Penetrant TestingNon-Destructive Testing, Destructive Testing, Advanced NDT, Third Party Inspection, Condenser Testing, Electrical Testing, Residual Life Assessment of Power Plant, O&M Services, Fitness For Service, Civil Testing and Training services.

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Ishita KapoorLiquid Penetrant Testing – Advantages, Disadvantages & Alternatives

Why use Ultrasonic Phased Array instead of Radiography?

by Ishita Kapoor on September 8, 2018

Radiography and ultrasound are the commendatory nondestructive testing (NDT) techniques that can volumetrically inspect welds and components for various defects like porosity, lack of fusion, cracks etc.
Choosing the right option often depends on external process decisions or small distinctions in the detection capability for a particular test. However, Ultrasound has progressed as a replacement for Radiography, not just in practice but also in the codes of major organizations like API (American Petroleum Institute) and ASME (American Society of Mechanical Engineers).

PA is often incorporated with time-of-flight diffraction (TOFD) while the inspectors use acquisition units and scanners that can accommodate both the methods simultaneously.

Here are the Typical Advantages of Ultrasound in comparison with Radiography:

  • Accurate sizing of defect height and less number of rejects or repair while using Engineering Critical Assessment:
    • Ultrasound permits defect height measurement, enabling volumetric consideration of flaw severity.
  • High chances of detection (POD), especially for cracks and lack of fusion:
    • In most studies, Ultrasound tends to detect planar flaws better than radiography.
  • Does not cause hazard, does not emit radiation, and does not require additional licensing or personnel.
  • Does not generate any waste material or chemical (as opposed to film-based radiography).
  • Work in proximity to ultrasonic testing can continue uninterrupted. Does not require screened-off areas.
  • Setup and inspection reports are in electronic format (as opposed to film format in radiography).
  • Real-time ultrasonic analysis of welds can provide instant assessment and feedback to a welder.


Here are the Requirements for Typical Ultrasonic Equipment and Inspection

  • A scan plan with a procedure documenting the inspection strategy and necessary parameters. Example: Parameters that are set up with the use of NDT SetupBuilder software.
  • An acquisition unit with position-encoding ability and full, raw A-scan data retention.

Example: An OmniScan flaw detector or FOCUS PX instrument.

  • An industrial scanner (with position encoder) to repeatedly scan a weld or component semi-automatically or automatically:
    • The choice of scanner model is based on the number of pipe diameter, welds, and other application variables.
  • Deliverable data:
    • The analysis is directly executed on the acquisition unit or by the use of post-analysis with TomoView, FocusPC PC software or OmniPC.
  • Alternative acceptance criteria, as required.
  • Probes, wedges, couplant delivery equipment, and other accessories.
  • Proper training and certification of personnel.
  • Demonstrated performance of equipment, procedure, operator, and inspection process.


Replacing radiography with ultrasound has become a code-approved practice as well as an industry trend. The phased array equipment is convenient to use, economical, compact and associated software are accelerating the use of ultrasound. The prime reasons for this continuing trend includes improved safety of operators and others in surrounding areas, savings in process cost and time and the use of alternative acceptance criteria. The expanded use of ultrasound has led to a decrease in part rejection and repairs.

About IRC Engineering Pvt. Ltd.

IRC is one of the fastest growing Testing and Inspection company in India. We at IRC provide Non-Destructive Testing, Destructive Testing, Advanced NDT, Third Party Inspection, Condenser Testing, Electrical Testing, Residual Life Assessment of Power Plant, O&M Services, Fitness For Service, Civil Testing and Training services.

read more
Ishita KapoorWhy use Ultrasonic Phased Array instead of Radiography?