Welding specifications

Types of NDT (non destructive tests)


The NDT methods shall be carried out in accordance with the general principles given in EN 12062 and with the requirements of the standard particular to each method:

PT:       penetrant testing according to EN 571-1;

MT:      magnetic particle inspection according to EN 1290;

UT:       ultrasonic testing according to EN 1714, EN 1713;

RT:       radiographic testing according to EN 1435.

                                                                     Table 1 - Abbreviation

Examination method


Eddy current examination

Magnetic particle examination

Penetrant examination

Radiographical examination

Ultrasonic examination

Visual examination







The figure below shows the typical defects in welds.

The NDT methods applied in testing of welded joints differ one from the other very much.

Visual inspection is the prior NDT method that should be done for the examination. The visual inspection provides basic information on the state of welded joints and the structure concerned.

Radiographic methods are most frequently used and permit a very reliable detection of three-dimensional discontinuities such as pores, non-metallic inclusions, incomplete penetration and undercuts at the inaccessible root side. The method seems to be less reliable in detecting planar, i.e. two-dimensional, defects such as cracks. The disadvantage of this method is the cost and that it requires particular skill for the realization.

The ultrasonic methods seem to be the most universally applicable. They may be applied to all types of defects but they are comparatively complicated and sensitive to various disturbances. They are less reliable, therefore, they are making themselves valued in welding very slowly.

Simple and reliable methods are available for detection of cracks reaching the surface. Magnetic methods are suitable for ferromagnetic materials, while penetrant methods are suitable for all metals.


The figure schematically shows the application of various NDT methods in testing butt and fillet welds.

The Destructive and non-destructive controls shall be defined by the inspector and the Director of the work, taking into account these general rules

  • VT (visual inspection) on all the welds (100%)
  • PT (penetrant testing) or MT (magnetic particle inspection) applies to fillet welds and partial welds
  • RT (radiographic testing) or UT (ultrasonic testing) applies to butt welds and T-joints

 RT generally is not suitable for fillet welds inspection.

RT is not


The guidance in Annex C of EN 12062:1997 should be followed.

The generally accepted methods for examination of welds are given in table 2 for the surface imperfections and in table 3 for internal imperfections.

For partial penetration welds and fillet welds the unfused root can prevent satisfactory volumetric examination when using the methods given in table 3.


Techniques other than those given in tables 2 and 3 can be agreed for determining the actual degree of penetration and the dimensions of other imperfection types.

The following table reports a reference guide about the main NDT methods. The table is taken from the good article from NDTnet .  

Table 1 - Reference Guide to Major Methods for the Nondestructive Examination of Welds



Detection of





Magnifying glass
Weld sizing gauge
Pocket rule
Straight edge
Workmanship standards

Surface flaws - cracks, porosity, unfilled craters, slag inclusions Warpage, underwelding, overwelding, poorly formed beads, misalignments, improper fitup

Low cost.
Can be applied while work is in process, permitting correction of faults.
Gives indication of incorrect procedures.

Applicable to surface defects only.
Provides no permanent record.

Should always be the primary method of inspection, no matter what other techniques are required. Is the only "productive" type of inspection.
Is the necessary function of everyone who in any way contributes to the making of the weld.


Commercial X-ray or gamma units made especially for inspecting welds, castings and forgings.
Film and p
rocessing facilities.
Fluoroscopic viewing equipment.

Interior macroscopic flaws - cracks, porosity, blow holes, nonmetallic inclusions, incomplete root penetration, undercutting, icicles, and burnthrough.

When the indications are recorded on film, gives a permanent record.
When viewed on a fluoroscopic screen, a low-cost method of internal inspection

Requires skill in choosing angles of exposure, operating equipment, and interpreting indications.
Requires safety precautions. Not generally suitable for fillet weld inspection.

X-ray inspection is required by many codes and specifications.
Useful in qualification of welders and welding processes.
Because of cost, its use should be limited to those areas where other methods will not provide the assurance required.


Special commercial equipment.
Magnetic powders - dry or wet form; may be fluorescent for viewing under ultraviolet light.

Excellent for detecting surface discontinuities -
especially surface cracks.

Simpler to use than radiographic inspection.
Permits controlled sensitivity.
Relatively low-cost method.

Applicable to ferromagnetic materials only.
Requires skill in interpretation of indications and recognition of irrelevant patterns.
Difficult to use on rough surfaces.

Elongated defects parallel to the magnetic field may not give pattern; for this reason the field should be applied from two directions at or near right angles to each other.

Liquid Penetrant

Commercial kits containing fluorescent or dye penetrants and developers.
Application equipment for the developer.
A source of ultraviolet light - if fluorescent method is used.

Surface cracks not readily visible to the unaided eye.
Excellent for locating leaks in weldments.

Applicable to magnetic and nonmagnetic materials. Easy to use. Low cost.

Only surface defects are detectable.
Cannot be used effectively on hot assemblies.

In thin-walled vessels will reveal leaks not ordinarily located by usual air tests. irrelevant surface conditions (smoke, slag) may give misleading indications.


Special commercial equipment, either of the pulse-echo or transmission type.
Standard reference patterns for interpretation of RF or video patterns.

Surface and subsurface flaws including those too small to be detected by other methods.
Especially for detecting subsurface lamination-like defects.

Very sensitive.
Permits probing of joints inaccessible to radiography.

Requires high degree of skill in interpreting pulse-echo patterns. Permanent record is not readily obtained.

Pulse-echo equipment is highly developed for weld inspection purposes.
The transmission-type equipment simplifies pattern interpretation where it is applicable.


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