Non-Destructive Tests for laymen in 10 minutes (2024)

Non-destructive tests (NDTs) are the most common modes of examination for Renewable and Energy Sector structures.

These tests are essentially designed to avoid “destroying” the welds that “glue” 2+ pieces of metals together while examining the integrity and strength of the welds.

Therefore the preferred modes of examining the welds are through non-destructive tests (NDTs) as they cause the least amount of damage to the finished products, and are faster alternatives than destructive tests where the more time-consuming mechanical and chemical tests take place in a lab.

DIN EN ISO-9712(2012) stipulated 10 ways of examining welds. They are ranked in terms of their applicability, starting with the most frequently seen in practice to the least frequent ones.

1. VT =Visual Testing

2. UT =Ultrasonic Testing

3. MT =Magnetic Particle Testing

4. RT =Radiographic Testing

5. LT =Leak Testing

6. PT =Penetration Testing

7. ET =Eddy Current Testing

8. AT =Acoustic Emission Testing

9. TT =Infrared Thermographic Testing

10. ST =Strain Gauge Testing

The idea is to detect any DISCONTINUITIES that weaken the strength of the weld.

However, it takes years of industry experience to master these seemingly straightforward, and instrument-assisted tests. Some of the common discontinuities are:

• Cracks

• Surface Pores

• Lack of Fusion

• Incomplete Penetration

• Undercut

• Crater

• Excessive Penetration at the Root/Excessive Reinforcement of the Weld

• Misalignment

• Concavity at the Root or Covering Layer

• Overlap

• Spatter

• Temper Colours

• Arc Strike

All tests are relatively easy to understand, as their modes of examination are exactly what they convey in words.

Visual Testings (VTs), for instance, usually require inspectors to visually inspect the weld to notice defects and Magnetic Particle Testings (MT) use handheld yokes to magnetize ferromagnetic materials. Powder magnets will cluster around discontinuities and allow defects that were missed in the first rounds of VTs to be captured.

VT is usually a MUST in all weld inspections, and they are accompanied by other modes of weld tests (items #2~#10) to facilitate and verify the initial visual examination. Sometimes you have more than 3 tests that are involved in one section of the weld, as each mode of NDT has its limitations.

The documents generated from these NDTs prove that the fabricated products are satisfactory and that once the fabricated products are handed over to the clients, the fabricators are not liable to lawsuits for defective products.

These documents also allow fabricators to claim compensation after the completion of fabrication, so they are very important in the project lifecycle.

Usually, these documents are produced by certified inspectors who have obtained official certifications from the American Welding Society (AWS), the International Institute of Welding (IIW), and the Welding Institute (TWI), which correspond to their respective certificates that are known to be CWI(Certified Welding Inspector), IWI (International Welding Inspector), and CSWIP (Certification Scheme for Weldment Inspection Personnel).

These certificates may be obtained through exams but the real training comes from experiences in the field. Rarely are the certificates alone sufficient if the certificate holder has no relevant work experience.