- horizontal rolled position (1G)
- horizontal fixed position (5G)
- pipe inclined fixed (6G)
- vertical position (2G).
Remember: these terms refer to the position of the pipe and not to the weld
Select the electrode that is best suited for the posi-tion and type of welding to be done. For the root pass of a multilayer weld, you need an electrode large enough, yet not exceeding 3/16 inch, that ensures complete fusion and penetration without undercutting and slag inclusions.
Do not assign a welder to a job under any of the following conditions listed below unless the welder and the work area are properly protected:
- When the atmospheric temperature is less than 0°F
- When the surfaces are wet
- When rain or snow is falling, or moisture is condensing on the weld surfaces
- During periods of high wind
In vertical arc welding, the current settings should be less than those used for the same electrode in the flat position. Another difference is that the current used for welding upward on a vertical plate is slightly higher than the current used for welding downward on the same plate.
Vertical welding is used on most types of joints. The types of joints you will most often use it on are tee joints, lap joints, and butt joints.
The previously described vertical welding techniques generally cover all types of electrodes; however, you should modify the procedure slightly when using E-7018 electrodes.
The AWS Weld Gauge is for accurate calibration of butt and fillet type welds. The redesigned gauge is pocket size and easy to operate. Weld convexity and concavity sizes have automatically been predetermined in accordance with AWS DI.I para 3.6.
Check The Throat Of Fillet Weld
Check Leg Size Of Fillet Weld
Either an X-ray machine or a radioactive source (Ir-192, Co-60, or in rare cases Cs-137) can be used as a source of photons. Neutron radiographic testing (NR) is a variant of radiographic testing which uses neutrons instead of photons to penetrate materials. This can see very different things from X-rays, because neutrons can pass with ease through lead and steel but are stopped by plastics, water and oils.
Since the amount of radiation emerging from the opposite side of the material can be detected and measured, variations in this amount (or intensity) of radiation are used to determine thickness or composition of material. Penetrating radiations are those restricted to that part of the electromagnetic spectrum of wavelength less than about 10 nanometres.
Inspection of welds
The beam of radiation must be directed to the middle of the section under examination and must be normal to the material surface at that point, except in special techniques where known defects are best revealed by a different alignment of the beam. The length of weld under examination for each exposure shall be such that the thickness of the material at the diagnostic extremities, measured in the direction of the incident beam, does not exceed the actual thickness at that point by more than 6%. The specimen to be inspected is placed between the source of radiation and the detecting device, usually the film in a light tight holder or cassette, and the radiation is allowed to penetrate the part for the required length of time to be adequately recorded.
The result is a two-dimensional projection of the part onto the film, producing a latent image of varying densities according to the amount of radiation reaching each area. It is known as a radiograph, as distinct from a photograph produced by light. Because film is cumulative in its response (the exposure increasing as it absorbs more radiation), relatively weak radiation can be detected by prolonging the exposure until the film can record an image that will be visible after development. The radiograph is examined as a negative, without printing as a positive as in photography. This is because, in printing, some of the detail is always lost and no useful purpose is served.
Before commencing a radiographic examination, it is always advisable to examine the component with one’s own eyes, to eliminate any possible external defects. If the surface of a weld is too irregular, it may be desirable to grind it to obtain a smooth finish, but this is likely to be limited to those cases in which the surface irregularities (which will be visible on the radiograph) may make detecting internal defects difficult.
After this visual examination, the operator will have a clear idea of the possibilities of access to the two faces of the weld, which is important both for the setting up of the equipment and for the choice of the most appropriate technique.
Defects such as delaminations and planar cracks are difficult to detect using radiography, which is why penetrants are often used to enhance the contrast in the detection of such defects. Penetrants used include silver nitrate, zinc iodide, chloroform and diiodomethane. Choice of the penetrant is determined by the ease with which it can penetrate the cracks and also with which it can be removed. Diiodomethane has the advantages of high opacity, ease of penetration, and ease of removal because it evaporates relatively quickly. However, it can cause skin burns.
Industrial radiography appears to have one of the worst safety profiles of the radiation professions, possibly because there are many operators using strong gamma sources (> 2 Ci) in remote sites with little supervision when compared with workers within the nuclear industry or within hospitals.
International Organization for Standardization (ISO)
- ISO 4993, Steel and iron castings – Radiographic inspection
- ISO 5579, Non-destructive testing – Radiographic examination of metallic materials by X- and gamma-rays – Basic rules
- ISO 10675-1, Non-destructive testing of welds – Acceptance levels for radiographic testing – Part 1: Steel, nickel, titanium and their alloys
- ISO 11699-1, Non-destructive testing – Industrial radiographic films – Part 1: Classification of film systems for industrial radiography
- ISO 11699-2, Non-destructive testing – Industrial radiographic films – Part 2: Control of film processing by means of reference values
- ISO 14096-1, Non-destructive testing – Qualification of radiographic film digitisation systems – Part 1: Definitions, quantitative measurements of image quality parameters, standard reference film and qualitative control
- ISO 14096-2, Non-destructive testing – Qualification of radiographic film digitisation systems – Part 2: Minimum requirements
- ISO 17636, Non-destructive testing of welds – Radiographic testing of fusion-welded joints
- ISO 19232, Non-destructive testing – Image quality of radiographs
- EN 444, Non-destructive testing; general principles for the radiographic examination of metallic materials using X-rays and gamma-rays
- EN 462-2, Non-destructive testing – image quality of radiographs – Part 2: image quality indicators (step/hole type) – determination of image quality value
- EN 462-3, Non-destructive testing – Image quality of radiogrammes – Part 3: Image quality classes for ferrous metals
- EN 462-4, Non-destructive testing – Image quality of radiographs – Part 4: Experimental evaluation of image quality values and image quality tables
- EN 462-5, Non-destructive testing – Image quality of radiographs – Part 5: Image quality of indicators (duplex wire type), determination of image unsharpness value
- EN 584-1, Non-destructive testing – Industrial radiographic film – Part 1: Classification of film systems for industrial radiography
- EN 584-2, Non-destructive testing – Industrial radiographic film – Part 2: Control of film processing by means of reference values
- EN 1330-3, Non-destructive testing – Terminology – Part 3: Terms used in industrial radiographic testing
- EN 1435, Non-destructive testing of welds – Radiographic testing of welded joints
- EN 2002-21, Aerospace series – Metallic materials; test methods – Part 21: Radiographic testing of castings
- EN 10246-10, Non-destructive testing of steel tubes – Part 10: Radiographic testing of the weld seam of automatic fusion arc welded steel tubes for the detection of imperfections
- EN 12517-1, Non-destructive testing of welds – Part 1: Evaluation of welded joints in steel, nickel, titanium and their alloys by radiography – Acceptance levels
- EN 12517-2, Non-destructive testing of welds – Part 2: Evaluation of welded joints in aluminium and its alloys by radiography – Acceptance levels
- EN 12679, Non-destructive testing – Determination of the size of industrial radiographic sources – Radiographic method
- EN 12681, Founding – Radiographic examination
- EN 13068, Non-destructive testing – Radioscopic testing
- EN 14096, Non-destructive testing – Qualification of radiographic film digitisation systems
- EN 14784-1, Non-destructive testing – Industrial computed radiography with storage phosphor imaging plates – Part 1: Classification of systems
- EN 14584-2, Non-destructive testing – Industrial computed radiography with storage phosphor imaging plates – Part 2: General principles for testing of metallic materials using X-rays and gamma rays
ASTM International (ASTM)
- ASTM E 94, Standard Guide for Radiographic Examination
- ASTM E 155, Standard Reference Radiographs for Inspection of Aluminum and Magnesium Castings
- ASTM E 592, Standard Guide to Obtainable ASTM Equivalent Penetrameter Sensitivity for Radiography of Steel Plates 1/4 to 2 in. [6 to 51 mm] Thick with X Rays and 1 to 6 in. [25 to 152 mm] Thick with Cobalt-60
- ASTM E 747, Standard Practice for Design, Manufacture and Material Grouping Classification of Wire Image Quality Indicators (IQI) Used for Radiology
- ASTM E 801, Standard Practice for Controlling Quality of Radiological Examination of Electronic Devices
- ASTM E 1030, Standard Test Method for Radiographic Examination of Metallic Castings
- ASTM E 1032, Standard Test Method for Radiographic Examination of Weldments
- ASTM 1161, Standard Practice for Radiologic Examination of Semiconductors and Electronic Components
- ASTM E 1648, Standard Reference Radiographs for Examination of Aluminum Fusion Welds
- ASTM E 1735, Standard Test Method for Determining Relative Image Quality of Industrial Radiographic Film Exposed to X-Radiation from 4 to 25 MeV
- ASTM E 1815, Standard Test Method for Classification of Film Systems for Industrial Radiography
- ASTM E 1817, Standard Practice for Controlling Quality of Radiological Examination by Using Representative Quality Indicators (RQIs)
- ASTM E 2104, Standard Practice for Radiographic Examination of Advanced Aero and Turbine Materials and Components
Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on concrete, wood and composites, albeit with less resolution. It is a form of non-destructive testing used in many industries including aerospace, automotive and other transportation sectors.
How it works
In ultrasonic testing, an ultrasound transducer connected to a diagnostic machine is passed over the object being inspected. The transducer is typically separated from the test object by a couplant (such as oil) or by water, as in immersion testing.
There are two methods of receiving the ultrasound waveform, reflection and attenuation. In reflection (or pulse-echo) mode, the transducer performs both the sending and the receiving of the pulsed waves as the “sound” is reflected back to the device. Reflected ultrasound comes from an interface, such as the back wall of the object or from an imperfection within the object. The diagnostic machine displays these results in the form of a signal with an amplitude representing the intensity of the reflection and the distance, representing the arrival time of the reflection. In attenuation (or through-transmission) mode, a transmitter sends ultrasound through one surface, and a separate receiver detects the amount that has reached it on another surface after traveling through the medium. Imperfections or other conditions in the space between the transmitter and receiver reduce the amount of sound transmitted, thus revealing their presence. Using the couplant increases the efficiency of the process by reducing the losses in the ultrasonic wave energy due to separation between the surfaces.
- Manual operation requires careful attention by experienced technicians
- Extensive technical knowledge is required for the development of inspection procedures.
- Parts that are rough, irregular in shape, very small or thin, or not homogeneous are difficult to inspect.
- Surface must be prepared by cleaning and removing loose scale, paint, etc., although paint that is properly bonded to a surface need not be removed.
- Couplants are needed to provide effective transfer of ultrasonic wave energy between transducers and parts being inspected unless a non-contact technique is used. Non-contact techniques include Laser and Electro Magnetic Acoustic Transducers (EMAT).
- Inspected items must be water resistant, when using water based couplants that do not contain rust inhibitors.
NDT Methods for Flaw Detection during Welding
Detectability of different defect types using TOFD
Institut de Soudure (FR)
Isotopen Technik Dr. Sauerwein GmBH (GER)
Nordon & CIE (FR)
The University of Surrey (UK)
After acquisition each scan was processed by the automated software to locate defect and component echoes. The effectiveness of the automatic defect identification process has been measured using the rating system shown in Table 1 for both the visibility of the defect and the level of associated false alarms. The full effectiveness of the algorithms was quantified by a comparison using full destructive testing of the testpieces, as performed by the Institut de Soudure.
The TIG welded testpieces contained a total of 15 defects of 6 types. The defects are abbreviated as follows:
LOFS – lack of side-wall fusion
RC – root crack
P – porosity
LOP – lack of penetration
W – weld inclusion
LOIRF – lack of inter-run fusion.
Three sets of 1m long testpieces were manufactured by Nordon, denoted sample TIG A, TIG B, and TIG C. Defects were intentionally positioned along the length of each weld at various stages of weld completion. Ultrasonic TOFD was performed at approx.: 10, 25, 50, 75, 85 and 90% weld completion.
The SA welded testpieces contained a total of 15 defects of 6 types. The defects are abbreviated as follows:
LOFS – lack of side-wall fusion
RC – root crack
P – porosity
LOI – lack of root (inter-run) fusion
SI – slag inclusion
LOIRF – lack of inter-run fusion.
Three sets of 1m long testpieces were manufactured by Nordon. Defects were intentionally positioned along the length of each weld at various stages of weld completion. Ultrasonic TOFD was performed at various stages of completion for each testpiece, from: 25, 30, 40, 50, 75, 80 and 100% weld completion.
Table 3 – Results of the automated signal processing software for the detection of defects in the SAW welded testpieces.
From the manual conventional NDT of the welds it can be summarised that the defects present in the SAW testpieces are of the intentional type and are located at the intended location. However, extra unintentional defects are present and the conventional ultrasonics fails to detect several defects (detected by radiography). Table 3 shows the results of the automated signal processing software for the detection of defects in the SAW welded testpieces.
The results of automatic processing of the high temperature TIG and SA scans acquired during welding have been presented. Overall the automated defect detection algorithms worked very well, demonstrating that weld flaw detection during welding is possible using the ultrasonic time of flight diffraction (TOFD) method. It should be noted that the parameters of the interpretation software required some ‘tuning’ between scans of different resolutions due to the different spatial resolution occupied by the defect and the differing signal-to-noise of the ultrasonic signal. The poorest performance was with the incomplete TIG welded specimens where the small amount of weld present causes difficulties for the defect detection algorithms.
During the automatic TOFD demonstration trials 64 scans were attempted, with 42 being processed by the signal processing algorithms. The majority of the unprocessed scans were due to either the affects of interference from other workshop welding equipment upon the encoder wheel or the poor quality of the initial TIG scans. With development work the interference problems should be overcome through the use of adequate shielding of the encoder and its cables. Examining the detectability at the various levels of weld completion, Table 4 shows the percentage of defects which can be detected at 25, 50, and 85% completion of the TIG welds. It should be recognised that there were very few TIG scans at low levels of completion which were suitable for processing. Table 5 shows the percentage of defects which can be detected at 25, 50, 80 and 100% weld completion of the SAW welds, again when compared against the interpretation of the testpieces when using conventional NDT techniques.
Bastos, T. F., Calderon, L., Martin, J.M. and Ceres, R., “Ultrasonic sensors and arc welding – a noisy mix”, Sensor Review, Vol. 16(3), pp. 26-32, 1996.
This note has been taken from the forthcoming paper Bonser, G.R. and Lawson, S.W., Defect detection in partially complete SAW and TIG welds using the ultrasonic time of flight diffraction method, Proc of SPIE Int Symp on Nondestructive Evaluation Techniques for Aging Infrastructure and Manufacturing, San Antonio, Texas, March 1998.
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MIG Welding Benefits
- All position capability
- Higher deposition rates than SMAW
- Less operator skill required
- Long welds can be made without starts and stops
- Minimal post weld cleaning is required
MIG Welding Shielding Gas
The shielding gas, forms the arc plasma, stabilizes the arc on the metal being welded, shields the arc and molten weld pool, and allows smooth transfer of metal from the weld wire to the molten weld pool. There are three primary metal transfer modes:
The primary shielding gasses used are:
- Argon – 1 to 5% Oxygen
- Argon – 3 to 25% CO2
CO2 is also used in its pure form in some MIG welding processes. However, in some applications the presence of CO2 in the shielding gas may adversely affect the mechanical properties of the weld.
Common MIG Welding Concerns
We can help optimize your MIG welding process variables. Evaluate your current welding parameters and techniques. Help eliminate common welding problems and discontinuities such as those listed below:
MIG Welding Problems
- Heavily oxidized weld deposit
- Irregular wire feed
- Unstable arc
- Difficult arc starting