Promoting smart solutions for welding-related industry. TOFD calibration blocks by ITMA. Production of defective specimens, and development of welding qualification procedures.

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Manufacturing welded joints with realistic defects. TOFD calibration
Blocks by ITMA
Ricardo Alvarez ITMA
Technological Services Manager
FUNDACION ITMA
Abstract
Intentional weld defect or flaw specimens can be required for training purposes, developing
new non‐destructive testing techniques, qualifying non‐destructive testing procedures
especially in case of TOFD qualification procedures, obtaining mechanical property data and in
support of safety cases.
The most important target in producing defects or imperfections is that they must accurately
simulate flaws which can suddenly appear in welded components and structures. For this
reason, in certain applications, machined slots or grooves which are more easily detected may
not be considered acceptable as planar defects for the NDT training or validation purposes. For
that reason Fundacion ITMA has developed techniques for producing realistic imperfections
and, in the case of cracks, the desired morphology, including shape, angles of tilt and skew to
the surface.
This document describes the Itma references, experiences and techniques used to obtain the
above mentioned defects and, for the most commonly required defect types, the qualification
procedure used by ITMA. This consists of inspecting by testing by surface crack detection,
measuring inside the slot, ultrasonic or radiographic inspection and/or sectioning to
demonstrate that the dimensional tolerance of the simulated imperfections can be generally
guaranteed within ±0.1mm in through‐wall extent and ±0.2mm in length.
Background
When summarising the work carried out within the Project for the Inspection of Steel
Components series, some authors concluded that the NDT procedure has to be validated and
tested on structures containing defects that, not being necessarily real ones, still do induce the
real physical phenomena that the inspection techniques must be able to handle. Some
technical papers stated that the use of very artificial discontinuities like side‐drilled holes or
flat‐bottomed‐holes to demonstrate the capabilities of NDT techniques often results in
optimistic reports and uncertain use of the technique on structures containing real defects.
When comparing the use of welded joints with real or artificial realistic flaws some advantages
could be listed for the latter [1]:
 Less expensive and time‐consuming fabrication
 The possibility of more certain characterisation
 The provision of non‐contaminated assemblies that can be more easily used for
effectiveness assessments
 The consideration of more relevant selections of structural geometry and material
ITMA can produce weld specimens with defects such as: lack of root fusion, lack of
penetration, lack of sidewall or inter‐run fusion, joint misalignment, porosity, solidification
cracking, cluster cracking, heat affected zone (hydrogen) cracking, undercut, brittle fracture or
fatigue cracks, slag inclusions or metallic slag. Some of these are essentially produced by using
controlled bad welding practice with techniques such as SAW, tungsten inert gas (TIG), CMT

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and CMT‐Pulse, operating automatic and robotic welding technology systems, high precision
machine tools and fatigue testing in complex structures. The majority of realistic defects
produced by ITMA are obtained by weld modification, and machining.
This document shows a few examples of the techniques used to obtain the realistic defects
and their application, for the different defect types. Details of the techniques not described in
this document are considered as ITMA industrial secret Knowhow.
Lack fusion defects and demonstration blocks
Lack of side wall or internal fusion defects are normally obtained with two techniques:
 TIG bridging
 Use of a metallic or non‐metallic insert.
The 'TIG bridging' technique consists of outlining the edges of the defect on the weld edge
with TIG runs, then bridging the area between them with further TIG runs, deposited so that
no fusion with the base metal is obtained.
Fundacion Itma has long experience in obtaining lack of side wall or internal fusion defects in
welded coupons and demonstration blocks for TOFD. Normally demonstration blocks are
obtained by using the metallic or non‐metallic insert technique. The procedure to manufacture
these demonstration blocks requires EDM notches located in internal parts of the welded
coupon. The demonstration blocks as required per ASME V appendix IX‐435 must correspond
to the following requirements:
The demonstration block shall be prepared by welding in order to permit the flaw location. Its
weld geometry shall be representative of the production details and its material and shape
shall be the same as the required to demonstrate the NDT system accuracy. WPS shall be used
as in the same production condition.
The EDM internal notches should be located according to the specification of ITMA customers
and in each case a non‐metallic or metallic insert is implanted inside the notch. The defect is
carefully closed on the weld edge by welding it in position with TIG runs and then completing
the weld according to the applicable welding procedure specification (WPS).
The contraction of the weld metal deposited to complete the weld is controlled carefully to be
sure that the insert is 'pushed' towards the weld edge producing a very tight defect, which
simulates the morphology of a real Lack of side wall or internal fusion defects. Both these
techniques allow a very accurate control of the defect size.
For a demonstration block, the TIG bridging technique could be less accurate control of the
defect size, especially in the materials were some cracks in welding could be expected.
Fundacion ITMA only produce defects for demonstration block with the insert technique
where the crack mouths do not tend to open due to solidification shrinkage of the weld;
hence, it is possible to obtain very tight and very precise defects by this method.
EDM notching
Machining or spark eroding are the most controlled ways to produce defects. Due to the
nature of the machining operation itself, such defects would be classified more as 'reference
reflectors' than 'realistic defects'. However, there are cases where according to the
requirements of the relevant code or standard and based on engineering considerations by

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NDT experts, the full control of the size, location and orientation of the deliberate defects is
more critical than their resemblance to a real defect. The location, orientation and sizes of the
defects to be inserted in the welds, are selected to match the acceptance criteria for ITMA
customer like for example ASME section XI article IWB‐3512.
Production of defective specimens at ITMA
The production of defective welds at ITMA usually involves three steps, which are detailed
below.
The first step when manufacturing a defective weld is to specify the type, quantities, location
(embedded, sub‐surface, surface breaking in HAZ, base metal or weld metal), orientation (tilt
and skew) and size of the defects, as well as the joint design and the welding procedure.
The joint design and the welding procedure are usually identical to that of the welds to be
inspected in production. On the other hand, there are some factors that will influence the
selection of defect types, sizes, locations and orientations:
‐Fracture mechanics aspects: a fracture mechanics based fitness‐for‐service assessment would
provide critical flaw sizes to be reproduced in the weld, to demonstrate that the selected NDT
technique is capable of detecting them.
‐In‐service experience: the defective weld may be designed to simulate actual defects found
on components in service, in order to develop inspection techniques to be applied to other
components operating in similar conditions.
Qualification tests
The exact size of the final deposited defect cannot be completely controlled during
manufacturing and can only be monitored by dimensional control of the EDM notches and
NDT of final defects.
In order to overcome these limitations and ensure that the defect obtained is as close as
possible to the required size, prior to the manufacturing of the defective welds, trial and
qualification samples for all required flaw types are manufactured.
These are typically welds in plates in which the required flaw types are implanted. A ITMA
internal qualification sequence is then applied, which is similar to that provided by welding
qualification standards) to qualify welding procedures and welders:
‐During manufacturing of the trial plate(s) the welding parameters and defect deposition
techniques are monitored and registered, so that they can be repeated when manufacturing
the actual defective weld.
‐After welding, the qualification samples are assessed by a combination of metallographic
evaluations (macro and micrographs) and radiographic inspection, aimed at measuring the
exact size of the implanted flaws and at assessing their morphology and any induced
metallurgical variations.
The obtained sizes are compared with the required ones and with acceptance criteria
(dimensional tolerances) selected by ITMA.

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A defect deposition procedure is considered satisfactory if these two conditions are satisfied:
The morphology of the realistic defect is similar to that of the corresponding real defect
The difference between the actual size of the defect and the required size is within ±0.5mm in
through‐wall extent, ±1mm in length, and ±0.2 mm in thickness of the defect.
If the qualification fails, the procedure is repeated
A number of defect sizes were measured within various confidential projects for the company
DF Caldereria pesada, for which the required defect through‐wall extent and length ranged
from 2.4 to 5.0 mm and 9.7 to 20.0mm, respectively, see references.
Manufacture of defective weld and final inspection
Once the qualification procedure is complete and it is has been demonstrated that all required
defect types can be deposited within the target tolerances on size, the defective welds are
manufactured. Following completion of the welds, UT/RX inspection is normally carried out to
verify that all required defects have been inserted and are detectable. Any additional
indication which does not correspond to any of the required defects is also recorded and in
case eliminate by reparation or manufacturing another new block.
Figure 1. Macrographic evaluation of calibration hole 1.5 on prequalification block 1.

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Figure 2. Macrographic evaluation of calibration hole 1.4 on prequalification block 1.
Figure 3. Macrographic evaluation of calibration hole 1.3 on prequalification block 1.

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Figure 4. Macrographic evaluation of calibration hole 1.2 on prequalification block 1.
Conclusions
‐It could be demonstrated that ITMA can reliably produce welded joints with realistic defects,
representative of the morphology of the most common defect types, and especially in the case
of defects for demonstration blocks
‐Using the different defect production techniques available at ITMA, mainly insert technique,
the dimensional tolerance of the realistic defects (ie actual size of the defect vs required size)
can be generally guaranteed within ±0.5mm in through‐wall extent, ±1mm in length, ±0.2 mm
in thickness.
‐A welding qualification procedure has been developed by ITMA, whereby welding trials
followed by metallographic assessment and NDT inspections are carried out and the results
assessed against the acceptance criteria.
‐To ensure consistency in defect size and morphology, manufacturing of the defective welds is
carried out with parameters and operation sequences similar to those recorded during welding
procedure qualification.