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The transition temperature is defined as the temperature midway between the upper shelf maximum toughness and lower shelf completely brittle.

Degrees Centigrade Three specimens are normally tested at each temperature Figure 4. Design engineers need to ensure that the toughness of the steel used for a particular item will be sufficient to avoid brittle fracture in service and so impact specimens are tested at a temperature related to the design temperature for the fabricated component.

C-Mn and low alloy steels undergo a sharp change in their resistance to brittle fracture as their temperature is lowered so that a steel that may have very good toughness at ambient temperature may show extreme brittleness at sub- zero temperatures. Method Test specimens are cooled to the specified test temperature by immersion in an insulated bath containing a liquid held at the test temperature.

After allowing the specimen temperature to stabilise for a few minutes it is quickly transferred to the anvil of the test machine and a pendulum hammer quickly released so that the specimen experiences an impact load behind the notch. The main features of an impact test machine are shown below.

Impact specimen on the anvil showing the hammer position at point of impact. Specimens are machined from welded test plates with the notch position located in different positions according to the testing requirements but typically in the centre of the weld metal and at positions across the HAZ. Increase in width of the back of the specimen behind the notch. After impact testing. Acceptance criteria Each test result is recorded and an average value calculated for each set of three tests.

Energy values are given in Joules or ft-lbs in US specifications. The energy absorbed by the hammer when it strikes each test specimen is shown by the position of the hammer pointer on the scale of the machine.

These values are compared with those specified by the application standard or client to establish whether specified requirements have been met. Three Impact test specimens are taken for each notch position as there is always some degree of scatter in the results.

A steel weldment with hardness above a certain maximum may be susceptible to cracking. A specimen that exhibits extreme brittleness will show a clean break. Specimens prepared for macroscopic examination can also be used for taking hardness measurements at various positions of the weldments.

A specimen that exhibits very good toughness will show only a small degree of crack extension. Methods There are three widely used methods: The hardness value is given by the size of the indentation produced under a standard load.

A typical hardness survey requires the indenter to measure the hardness in the base metal on both sides of the weld. The Brinell method gives an indentation too large to accurately measure the hardness in specific regions of the HAZ and is mainly used to measure the hardness of base metals.

Both the Vickers and Rockwell methods are suitable for carrying out hardness surveys on specimens prepared for macroscopic examination of weldments. The Vickers method of testing is illustrated below.

A V notch is machined at the centre of the bar. Vickers method. This data is essential for making an appropriate decision when a crack is discovered during inspection of equipment that is in-service. Fracture toughness data enables engineers to carry out fracture mechanics analyses such as: Rockwell method.

A shallow saw cut is made at the bottom of the notch and the specimen put into a machine that induces a cyclic bending load until a shallow fatigue crack initiates from the saw cut. Specimens A CTOD specimen is prepared as a rectangular or square shaped bar cut transverse to the axis of the butt weld.

A typical hardness survey using Vickers hardness indenter is shown below: Brinell method. Hardness values are shown on test reports as a number followed by letters indicating the test method. Objective Charpy V notch testing enables engineers to make judgements about the risk of brittle fracture occurring in steels.

Method CTOD specimens are usually tested at a temperature below ambient and the specimen temperature is controlled by immersion in a bath of liquid cooled to the required test temperature. The test piece details are shown below. The specimens are relatively large. The figures below illustrate the main features of the CTOD test. A load is applied to the specimen to cause bending and induce a concentrated stress at the tip of the crack and a clip gauge.

For each test condition position of notch and test temperature it is usual to carry out three tests. Some degree of ductility is also demonstrated. CTOD values are expressed in millimetres. Acceptance criteria An application standard or client may specify a minimum CTOD value that indicates ductile tearing.

A very tough steel weldment will allow the mouth of the crack to open widely by ductile tearing at the tip of the crack whereas a very brittle weldment will tend to fracture when the applied load is quite low and without any extension at the tip of the crack.

Fracture toughness is expressed as the distance the crack tip opens without initiation of a brittle crack. Subjecting specimens to bending is a simple way of verifying there are no significant flaws in the joint.

The clip gauge enables a chart to be generated showing the increase in width of the crack mouth against applied load from which a CTOD value is calculated. Method Guided bend tests are usually used for welding procedure and welder qualification.

Guided means that the strain imposed on the specimen is uniformly controlled by being bent around a former with a certain diameter. The diameter of the former used for a particular test is specified in the code, having been determined by the type of material being tested and the ductility that can be expected from it after welding and any PWHT.

The diameter of the former is usually expressed as a multiple of the specimen thickness t and for C-Mn steel is typically 4t but for materials that have lower tensile ductility the radius of the former may be greater than 10t.

Acceptance criteria Bend tests pieces should exhibit satisfactory soundness by not showing cracks or any signs of significant fissures or cavities on the outside of the bend. Small indications less than about 3mm in length may be allowed by some standards. This method for assessing the quality of fillet welds may be specified by application standards as an alternative to macroscopic examination. It is a test method that can be used for welder qualification testing according to European Standards but is not used for welding procedure qualification.

The notch profile may be square, V or U shape. Method Specimens are made to fracture through their throat by dynamic strokes hammering or by pressing, as shown below. The welding standard or application standard will specify the number of tests typically four. Acceptance criteria The standard for welder qualification, or application standard, will specify the acceptance criteria for imperfections such as lack of penetration into the root of the joint and solid inclusions and porosity that are visible on the fracture surfaces.

Test reports should also give a description of the appearance of the fracture and location of any imperfection. Butt weld fractures nick-break tests Objective The same as for fillet fracture tests. These tests are specified for welder qualification testing to European Standards as an alternative to radiography and are not used for welding procedure qualification testing.

Specimens Taken from a butt weld and notched so that the fracture path will be in the central region of the weld. Typical test piece types are shown below. Acceptance criteria The standard for welder qualification or application standard will specify the acceptance criteria for imperfections such as lack of fusion, solid inclusions and porosity that are visible on the fracture surfaces. BS EN ISO Destructive tests on welds in metallic materials - impact tests - test specimen location, notch orientation and examination.

Part 1: Method of test at ambient temperature. Part 5: Method of test at elevated temperatures. When this presentation has been completed you should be able to recognise a wide range of mechanical tests and their purpose. You should also be able to make calculations using formulae and tables to determine various values Destructive Testing of strength, toughness, hardness and ductility. Destructive Testing Definitions Destructive Tests.

What is destructive testing? Destructive tests include: Bend test the joint materials. Qualitative and Quantitative Tests Definitions.

The following mechanical tests have units and are termed Mechanical properties of metals are related to the quantitative tests to measure mechanical properties of amount of deformation which metals can withstand the joint. The following mechanical tests have no units and are under static compressive termed qualitative tests for assessing weld quality. Mechanical Test Samples Destructive Testing. Tensile specimens Welding procedure qualification testing CTOD specimen Top of fixed pipe 2 Typical positions for test pieces and specimen type position.

Hardness tests: Typical location of the indentations Vickers hardness tests: Adjustable Diamond Indentation shutters indentor. Information to be supplied on the test report: Anvil support ASTM: American Society of Testing Materials. Machined notch. Three specimens are normally tested at each temperature. Refers to materials Different tensile tests: Measuring the overall strength of the weld joint.

Reporting results: Two marks are made Two marks are made Gauge length 50mm Gauge length 50mm. During the test, yield and tensile strength are recorded During the test, yield and tensile strength are recorded The specimen is joined and the marks are re-measured The specimen is joined and the marks are re-measured. The cross sectional area before testing was 10mm in depth and 40mm in width.

The specimen before testing mm long and after testing had a length mm. Will reveal: P grit paper. Bend testing can also be used to give an assessment of weld zone ductility. To determine the soundness of the weld zone. Bend Testing There are three ways to perform a bend test: Root bend Face bend Side bend Side bend tests are normally carried out on welds over 12mm in thickness. Defect indication generally this specimen would be unacceptable. Acceptance for minor ruptures on tension surface depends upon code requirements.

Have Qualitative: Vessel configuration: In most cases this sensor is radiographic film. These devices facilitate so-called real-time radiography and examples may be seen in the security check area at airports. Low energy radiations are more easily absorbed and the presence of low energy radiations within the X-ray beam. Up to keV they are generated by conventional X-ray tubes which.

Portability falls off rapidly with increasing kilovoltage and radiation output. Above keV X-rays are produced using devices such as betatrons and linear accelerators. The present discussion is confined to film radiography since this is still the most common method applied to welds. Other forms of penetrating radiation exist but are of limited interest in weld radiography.

The transmitted radiation is collected by some form of sensor. Radium sources were also extremely hazardous to the user due to the production of radioactive radon gas as a product of the fission reaction. Since the advent of the nuclear age it has been possible to artificially produce isotopes of much higher specific activity than those occurring naturally which do not produce hazardous fission products. All sources of X-rays produce a continuous spectrum of radiation.

Conventional X-ray units are capable of performing high quality radiography on steel of up to 60mm thickness. The activity of these sources was not very high so they were large by modern standards even for quite modest outputs of radiation and the radiographs produced were not of a particularly high standard.

Their relative advantages and limitations are discussed in terms of their applicability to the examination of welds. Digital technology has enabled the storing of radiographs using computers. It has a relatively and high specific activity and output sources with physical dimensions of mm in common usage. This lack of sensitivity to planar defects makes radiography unsuitable where a fitness-for-purpose approach is taken when assessing the acceptability of a weld.

Ytterbium has only fairly recently become available as an isotope for industrial use. Cobalt 60 has an energy approximating that of 1. Thulium Four isotopes in common use for the radiography of welds. In terms of steel thulium 90 is useful up to a thickness of about 7mm. Planar defects such as cracks or lack of sidewall or inter-run fusion are much less likely to be detected by radiography since they may cause little or no change in the penetrated thickness.

They are useful for the radiography of steel in mm of thickness. Iridium is probably the most commonly encountered isotopic source of radiation used in the radiographic examination of welds. Against this the quality of radiographs produced by gamma ray techniques is inferior to those produced by X-ray the hazards to personnel may be increased if the equipment is not properly maintained or if the operating personnel have insufficient training and due to their limited useful lifespan new isotopes have to be downloadd on a regular basis so that the operating costs may exceed those of an X-ray source.

Gamma sources produce a number of specific quantum energies unique for any particular isotope. Volumetric weld defects such as slag inclusions except in special cases where the slag absorbs radiation to a greater extent than does the weld metal and various forms of gas porosity are easily detected by radiographic techniques due to the large negative absorption difference between the parent metal and the slag or gas. Where defects of this type are likely to occur other NDE techniques such as ultrasonic testing are preferable.

The major advantages of using isotopic sources over X-rays are: Unlike X-ray sources gamma sources do not produce a continuous distribution of quantum energies. Figure 5. The same laws of physics apply to ultrasonic waves as to light waves. Because sound is reflected at a boundary between two materials having different acoustic properties ultrasound is a useful tool for the detection of weld defects.

When ultrasonic waves pass from a given material with a given sound velocity to a second material with different velocity. Since velocity is a constant for any given material and sound travels in a straight line with the right equipment ultrasound can also be used to give accurate positional information about a given reflector. Ultrasonic waves are refracted at a boundary between two materials having different acoustic properties so probes may be constructed which can beam sound into a material at within certain limits any given angle.

Careful observation of the echo pattern of a given reflector and its behaviour as the ultrasonic probe is moved together with the positional information obtained above and knowledge of the component history enables the experienced ultrasonic operator to classify the reflector as slag. An ultrasonic probe: Simplified probe arrays have greatly reduced the complexity of setting-up the automated system to carry out a particular task. A flaw detector: Automated systems generate very large amounts of data and make large demands upon the RAM of the computer.

Recent advances in automated UT have led to a reduced amount of data being recorded for a given length of weld. Automated UT systems now provide a serious alternative to radiography on such constructions as pipelines where a large number of similar inspections allow the unit cost of system development to be reduced to a competitive level.

Automated or semi-automated systems for ultrasonic testing the same basic use equipment although since in general this will be multi-channel it is bulkier and less portable. Probes for automated systems are set in arrays and some form of manipulator is necessary to feed positional information about them to the computer.

Such equipment is lightweight and extremely portable. These leakage fields attract magnetic particles finely divided magnetite to themselves leading to the formation of an indication.

The leakage field will be greatest for linear discontinuities at right angles to the magnetic field so for a comprehensive test the magnetic field must normally be applied in two directions. The test is economical to carry out in terms of equipment cost and rapidity of inspection and the level of operator training required is relatively low.

Fluorescent magnetic particles normally provide the greatest sensitivity in a liquid suspension. The magnetic particles may be visibly or fluorescently pigmented to provide contrast with the substrate or conversely the substrate may be lightly coated with a white background lacquer to contrast with the particles. In certain cases dry particles may be applied by a gentle jet of air.

Advantages Limitations Inexpensive equipment Only magnetic materials Direct location of defect May need to demagnetise components Surface conditions not critical Access may be a problem for the yoke Can be applied without power Need power if using a yoke Low skill level No permanent record Sub-surface defects found mm Calibration of equipment Quick.

Use of fluorescent dyes considerably increases the sensitivity of the technique. Provided by either visible or fluorescent dyes. If there is a suitable contrast between the penetrant and the developer an indication visible to the eye will be formed.

Penetrant which has entered a tight discontinuity will remain even when the excess is removed. Application of a suitable developer will encourage the penetrant within discontinuities to bleed out. Ultrasonic inspection may not detect near-surface defects easily since the indications may be masked by echoes arising from the component geometry and should therefore be supplemented by an appropriate surface crack detection technique for maximum test confidence.

Non Destructive Testing Objective When this presentation has been completed you will have a greater understanding of and recognise various NDT methods and their differences. Radiographic inspection RT. Dye penetrant inspection PT. Magnetic particle inspection MT. Each technique has advantages and 3. The choice of NDT techniques is based on consideration of these advantages and disadvantages.

Ultrasonic inspection UT. Clean off penetrant Step 3: Penetrant Testing Penetrant Testing Step 1: Pre-cleaning Step 2: These inks require a UV-A light source and a darkened viewing area to inspect the component. Ultrasonic Testing Main features: Advantages surface detection. Image quality indicator Radiation beam Densitometer Test specimen Contrast. Generated by the decay Test specimen of unstable atoms. What determines the penetrating power of an X-ray? What determines the penetrating power of a gamma ray?

Table 6. Production welds made in accordance with welding conditions similar to those used for a test weld should have similar properties and therefore be fit for their intended purpose. Demonstrating the mechanical properties of the joint is the principal purpose of qualification tests.

Welders need to be able to understand WPSs. Although WPSs are shopfloor documents to instruct welders. Control of welding is by WPSs that give detailed written instructions about the welding conditions that must be used to ensure that welded joints have the required properties.

The test coupon is subjected to NDT in accordance with the methods specified by the Standard — visual inspection. AWS D1. Some alternative ways that can be used for writing qualified WPSs for some applications are: The principal American Standards for procedure qualification are: Part 2 Arc welding of aluminium and its alloys.

A successful procedure qualification test is completed by the production of a WPQR. The principal European Standards that specify these requirements are: Part 1 Arc and gas welding of steels and arc welding of nickel and nickel alloys.

MMA Manual Most of the welding variables classed as essential are the same in both the European and American Welding Standards but their qualification ranges may differ.

The welding conditions that are allowed to be written on a qualified WPS are referred to as the qualification range and depend on the welding conditions used for the test piece as-run details and form part of the WPQR.

If a welder makes a production weld using conditions outside the range given on a particular WPS there is a danger that the welded joint will not have the required properties and there are two options: Some application standards specify their own essential variables and it is necessary to ensure these are considered when procedures are qualified and WPSs written.

Examples of essential variables according to European Welding Standards are given in Table 6. Welding conditions are referred to as welding variables by European and American Welding Standards and are classified as either essential or non- essential variables and can be defined as: Because essential variables can have a significant effect on mechanical properties they are the controlling variables that govern the qualification range and determine what can be written in a WPS.

Welding Standards have been developed to give guidance on which test welds are required to show that welders have the required skills to make certain types of production welds in specified materials. Parent material Parent materials of similar composition and mechanical type properties are allocated the same Material Group No. Joints tested as-welded only qualify as-welded production joints. Welding Consumables for production welding must have the same consumables European designation —general rule.

Material thickness A thickness range is allowed — below and above the test coupon thickness. Welders also need to have the skill to consistently produce sound defect-free welds. Preheat The preheat temperature used for the test is the minimum that temperature must be applied.

Interpass The highest interpass temperature reached in the test is the temperature maximum allowed. Variable Range for procedure qualification Welding process No range — process qualified must be used in production. Type of current AC only qualifies for AC. Part 2: Aluminium and aluminium alloys. American Standards allow welders to demonstrate they can produce sound welds by subjecting their first production weld to NDT.

The principal American Standards that specify requirements for welder qualification are: EN Welding personnel — Approval testing of welding operators for fusion welding and resistance weld setters for fully mechanised and automatic welding of metallic materials. For manual and semi-automatic welding tests demonstrate the ability to manipulate the electrode or welding torch.

For mechanised and automatic welding the emphasis is on demonstrating the ability to control particular types of welding equipment. The welding engineer writes a WPS for a welder qualification test piece. Figure 6. Some welding variables classed as essential for welder qualification are the same types as those classified as essential for welding procedure qualification.

Material thickness A thickness range is allowed. Pipe diameter Essential and very restricted for small diameters: Variable Range for welder qualification Welding process No range — process qualified is the process that a welder can use in production. A variable that if changed beyond the limits specified by the Welding Standard may require greater skill than has been demonstrated by the test weld.

Examples of welder qualification essential variables are given in Table 6. The range of qualification is based on the limits specified by the Welding Standard for welder qualification essential variables. Welding positions Position of welding very important. H-L allows all positions except PG. Fillet welds only qualify fillets. Some essential variables are specific to welder qualification. Filler material Electrodes and filler wires for production welding must be within the range of the qualification of the filler material.

Type of weld Butt welds cover any type of joint except branch welds. The welder is working for the same manufacturer. Valid for two years provided that: Retest every three years. MMA Manual Nb: We will however discuss the contents of WPQR and its associated documentation. This section does not state how to Welding Procedures write a procedure to a code as this is the duty.

Welding procedure qualification record WPQR. What is the test trying to show? Preliminary welding procedure specification Answer: To show that the welded joint has the pWPS. WPS Objective When this presentation has been completed you will have a greater understanding of the terminology used in welding and welder documentation and the order in which it should be completed. Welding procedure specification WPS. A variable. Some typical additional variables Note: The application standard.

Welding procedure qualification record WPQR details: Production welding conditions must remain within The welding conditions used for the test weld the range of qualification allowed by the WPQR.

Welding Procedures Welding Procedures Producing a welding procedure involves: Welding of Pipelines.

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Class 1 Welding of Steel Pipe Work. If a customer queries the approval evidence can be Thermal heat treatments supplied to prove its validity. Structural Steel Welding Code.

Welding of Pipelines over 7 Bar. Example codes: MIG Other quirks MAG Range of approval MMA SAW Plasma Arc approval test. Parent metal thickness. Each fillet weld shall For branch connections and fillet welds.

Thickness definitions Note 2: Parent metal thickness at the joint. For special applications only. Replaced BS EN a is the throat as used for the test piece. Expressed in kilo Joules work piece. The range of qualification allowed for production welding is The test weld may need to be destructively tested. When welding in accordance with a Qualified the WPS. What is the main reason for qualifying An approved WPS should be available covering the a welder?

MT or range of qualification shown on the Certificate. Party Inspector as a true record of the test. Examining Body or Third Party Inspector may be required to monitor the qualification process. Object of a welding qualification test: Welder Qualification Any Questions? J2 Longitudinal Charpy. There are three essential aspects to material inspection that the Inspector should consider: S Structural steel.

Guidelines for a metallic material grouping system and steel producer and welding consumable data books can also provide the inspector with guidance as to the suitability of a material and consumable type for a given application.

These materials are all widely used in fabrication. A commonly used material standard for steel designation is BS EN — Hot rolled products of non-alloy structural steels. A wide range of materials can be used in fabrication and welding and include.

For example materials standards such as BS EN. Commonly used materials and most of the alloys can be fusion welded using various welding processes. A typical steel designation to this standard. G3 Normalised or normalised rolled. Reference to other standards such as ISO Welding. With a welded product. BS EN Metallic products — Types of inspection documents is the standard which provides guidance on these types of document.

According to BS EN inspection documents fall into two types: To trace the history of the material. On smaller diameter pipes it may be stencilled along the outside of the pipe. Application or location of a particular material can be carried out through a review of the WPS.

On large diameter pipes this information is usually stencilled on the inside of the pipe. In certain circumstances the inspector may have to witness the transfer of cast numbers from the original plate to pieces to be used in production. On pipeline work it is a requirement that the inspector records all the relevant information for each piece of linepipe.

Specific inspection Quality management system of the material manufacturer certified by a competent body established within the community and having undergone a specific assessment for materials.

BS EN Metallic materials Summary of types of inspection documents. Inspection document Type 2. Inspection certificate Type 3. General inspection This takes account of storage conditions. Figure 7. Visible imperfections Typical visible imperfections are usually attributable to the manufacturing process and include cold laps which break the surface or laminations if they appear at the edge of the plate.

Surface condition The surface condition is important and must not show excessive millscale or rust. At this stage of inspection the material cast or heat number may be recorded for validation against the material certificate. The points for inspection must include: Ultrasonic testing using a compression probe may be required for laminations which may be present in the body of the material.

Dimensions For plates this includes length. For pipes this includes length and wall thickness and also inspection of diameter and ovality. Steel surface which has begun to rust and from which mill scale has begun to flake.

Slight pitting visible under normal vision. Steel surface largely covered with adherent millscale with little or no rust. Steel surface on which mill scale has rusted away. General pitting visible under normal vision. There are four grades of rusting which the inspector may have to consider: Steel surface on which the mill scale has rusted away or from which it can be scraped. These types of test are normally conducted by an approved test house but sometimes on. If material type cannot be determined from the inspection documents available or the inspection document is missing.

This can be difficult if the material is not readily accessible. These methods may include but are not limited to: Spark test. Nickel and nick alloys. Part 3. Arc welding of aluminium and aluminium alloys. Charpy impact tests on metallic materials. Arc welded joints in steel. BS EN Filler rods and wires for stainless steels. Arc welding of ferritic steels. BS EN Fluxes for submerged arc welding. Guidance on quality levels for imperfections. Wire electrodes and flux wire combinations for submerged arc welding of non-alloy and fine grain steels.

Classification of imperfections in metallic fusion welds. Designation systems for steels. Non-destructive examination of welds — Radiographic examination of welded joints. Definition and classification of grades of steel.

Fusion welding. Covered electrodes for manual metal arc welding of non-alloy and fine grain steels. Metallic products — Types of inspection documents. Nomenclature of processes and reference numbers for symbolic representation on drawings. Destructive tests on welds in metallic materials.

Part 2. General guidance for arc welding. ISO Part 2 Aluminium and aluminium alloys. Qualification based on pre-production-welding test. Qualification based on tested welding consumables. Part 8 Welding of tubes to tube-plate joints. Arc and gas welding of steels and arc welding of nickel and nickel Part 1 alloys.

Part 12 Spot. Part 6 Copper and copper alloys. Qualification based on previous welding experience. Metal welding processes. ISO Specification and qualification of welding procedures for metallic materials.

Part 2 Arc welding of aluminium and its alloys. Arc welding. ISO Welding — Guidelines for a metallic material grouping system. ISO Specification and qualification of welding procedures for metallic materials — General rules. ISO Specification and qualification of welding procedures for metallic Materials — Welding procedure test.

Part 9 Underwater hyperbaric wet welding. Does not overburden the drawing. No need for an additional view — all welding symbols can be put on the main assembly drawing. An alternative method is to use a symbolic representation to specify the required information — as shown below for the same joint detail. Symbolic representation has following disadvantages: Symbolic representation has the following advantages: Some training is necessary in order to interpret the symbols correctly.

There is not a way of giving precise dimensions for joint details. Elementary welding symbols Various types of weld joint are represented by a symbol that is intended to help interpretation by being similar to the shape of the weld to be made. Examples of symbols used by EN are shown on the following pages.

European Standard EN — Welded. Details of the European Standard are given in the following sub-sections with only brief information about how the American Standard differs from the European Standard. Examples of supplementary symbols and how they are applied are given below. Designation Flat flush single V butt weld Illustration of joint preparation Symbol Convex double V butt weld Concave fillet weld Flat flush single V butt weld with flat flush backing run Single V butt weld with broad root face and backing run Fillet weld with both toes blended smoothly Note: If the weld symbol does not have a supplementary symbol then the shape of the weld surface does not need to be indicated precisely.

This is done. An example of how a single bevel butt joint should be represented. It can be at either end of the joint line and it is the draughtsman who decides which end to make the arrow side. The arrow side is always the end of the joint line that the arrow line points to and touches. The figure below illustrates these principles. In case of a non-symmetrical joint.

It joins one end of the continuous reference line. The convention for doing this is: For a non-symmetrical weld it is essential that the arrow side and other side of the weld be distinguished. Symbols for the weld details on other side must be placed on the dashed line.

This flexibility of the position of the continuous and dashed lines is an interim measure that EN allows so that old drawings to the obsolete BS Part 2. Fillet weld leg length. Penetration depth.

Absence of any indication to the contrary. Some examples of how these symbols are used are shown below. Length dimensions for the weld are written on the right-hand side of the symbol. Dashed line not required because itit is a symmetrical weld Note: A closed tail can also be used into which reference to a specific instruction can be added. The major differences are: For consumable electrode welding processes. The arc generates heat for fusion of the base metal.

Heat input to the fusion zone depends on the voltage. With the exception of TIG welding. The ionised gas enables a current to flow across the gap between electrode and base metal thereby creating an arc.

For TIG welding. The discharge causes a spark to form which causes the surrounding gas to ionise.

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Heat input values into the weld for various processes can be calculated from the arc energy by multiplying by the following thermal efficiency factors. The thermal efficiency factor is the ratio of heat energy introduced into the welding arc to the electrical energy consumed by the arc. Overhead welding tends to give low heat input because of the need to use low current and relatively fast travel speed.

Welding in the flat position downhand can be a low or high heat input position because the welder has more flexibility about the travel speed that can be used.

Of the arc welding processes. Horizontal-vertical welding is a relatively low heat input welding position because the welder cannot weave in this position. Welding position and the process have a major influence on the travel speed that can be used. For manual and semi-automatic welding the following are general principles: For processes where the arc voltage is controlled by the power source SAW.

Vertical-down welding tends to give the lowest heat input because of the fast travel speed that can be used. Polarity Polarity determines whether most of the arc energy the heat is concentrated at the electrode surface or at the surface of the parent material.

Minimises arc blow. As a general rule.

Penetration depth affects dilution of the weld deposit by the parent metal and it is particularly important to control this when dissimilar metals are joined. This relationship is known as the power source static characteristic and power sources are manufactured to give a constant current or a constant voltage characteristic. The welder tries to hold a fairly constant arc length B in Figure 1 for the current Y that has been set.

For the operating principle of this type of power source see Figure 1. A welder has to work within a fairly narrow range of arc length for a particular current setting — if it is too long the arc will extinguish and if it is too short the electrode may stub into the weld pool and the arc will be extinguished. Once an arc has been struck and stabilised. The Volt-Amp relationship for a constant current power source is shown in Figure 1.

The power source is designed to ensure that these small changes in arc voltage during normal welding will give only small changes in current X to Z. The higher current Z. Wire feed speed and current are directly related so that as the current is increased. The operating principle of this type of power source is shown in Figure 2 A welder sets the voltage B and the current Y on the power source. The most versatile of the welding processes.

When an arc is struck between the coated electrode and workpiece. The flux forms gas and slag. It involved a bare metal rod with no flux coating to give a protective gas shield. The process allows only short lengths of weld to be produced before a new electrode needs to be inserted in the holder.

The final weld quality is primarily dependent on the skill of the welder. The development of coated electrodes did not occur until the early s. It can be used in all positions. The molten slag solidifies. Electrode angle o to the horizontal Consumable electrode Filler metal core Flux coating Direction of electrode travel Solidified slag Arc Gaseous shield Molten weld pool Parent metal Weld metal The manual metal arc welding process.

MMA welding is suitable for welding most ferrous and non-ferrous metals. A constant welding current. The arc length may change during welding. For MMA welding a power source with a constant current drooping output must be used. AC welding current flows from negative to positive. The power source must provide: Welding voltage to maintain the arc during welding. Amperage too low: Poor fusion or penetration. Arc voltage too high: Excessive spatter.

Welding current level is determined by the size of electrode. Arc voltage is a function of arc length. Amperage controls burn off rate and depth of penetration. For safety reasons the OCV should not exceed V. Arc voltage is the voltage required to maintain the arc during welding and is usually between V.

With MMA the welder controls the arc length and therefore the arc voltage. Arc voltage controls weld pool fluidity. The effects of having the wrong arc voltage can be: Arc voltage too low: Poor penetration. Amperage too high: Excessive penetration. Direct current DC Direct current is the flow of current in one direction. Travel speed too slow: Cold lap. The preferred polarity of the MMA system depends primarily upon the electrode being used and the desired properties of the weld.

The potential defects associated with incorrect welding speeds when using the MMA welding process are: Travel speed too fast: Narrow thin weld bead. For MMA welding it refers to the polarity of the electrode. Electron flow direction is from the workpiece to the electrode. When the electrode is on the positive pole of the welding circuit. The distribution of energy is now reversed. The welding arc when using direct current can be affected by arc blow. The deflection of the arc from its normal path due to magnetic forces.

When the electrode is positively charged DCEP and the workpiece is negatively charged this has the effect of generating two thirds of the available heat energy at the tip of the electrode. Alternating current is the flow of current in two directions. One third of the available heat energy is generated at the tip of the electrode. With alternating current. Electron flow direction is from the electrode to the workpiece. Alternating current AC The current alternates in the welding circuit.

Direct current with a negatively charged electrode DCEN causes heat to build up on the electrode. Weld deposit can be coarse and with fluid slag. These electrodes are easy to use in any position and are noted for their use in the stovepipe welding technique. Rutile electrodes contain a high proportion of titanium oxide rutile in the coating.

Titanium oxide promotes easy arc ignition. This makes the slag coating more fluid than rutile coatings. They can be used with AC and DC power sources and in all positions. These electrodes are general purpose electrodes with good welding properties. These electrodes are used for welding medium and heavy section fabrications where higher weld quality. A welding process OF can be directly linked to productivity. TIG welding is a process where melting is produced by heating with an arc struck between a non-consumable tungsten electrode and the workpiece.

An inert gas is used to shield the electrode and weld zone to prevent oxidation of the tungsten electrode and atmospheric contamination of the weld and hot filler wire as shown below. Tungsten electrode types Different types of tungsten electrodes can be used to suit different applications: They have higher current carrying capacity than pure tungsten electrodes and maintain a sharp tip for longer.

Electrode grinding machines used for thoriated tungsten grinding should be fitted with a dust extraction system. Operating characteristics of these electrodes fall between the thoriated types and pure tungsten. However, since they are able to retain a balled end during welding, they are recommended for AC welding. Also, they have a high resistance to contamination and so they are used for high integrity welds where tungsten inclusions must be avoided.

Shielding gases The following inert gases can be used as shielding gases for TIG welding: Less change in arc voltage with variations in arc length. Lower than with helium, which gives reduced penetration. Argon is heavier than air, so requires less gas to shield in the flat and horizontal positions.

Also, better draught resistance. Obtained from the atmosphere by the separation of liquefied air — lower cost and greater availability. Performance item Arc voltage Helium Higher than with argon. Arc is hotter which is helpful in welding thick sections and viscous metals eg nickel.

High, which can be of advantage when welding metals with high thermal conductivity and thick materials. Helium is lighter than air and requires more gas to properly shield the weld. Obtained by separation from natural gas — lower availability and higher cost. For pipe welding.

Air tends to be sucked in from the surrounding atmosphere and this may also lead to porosity and contamination. For C and C-Mn steels it is possible to make satisfactory welds without a back purge. Back purging should continue until two or more weld layers of weld have been deposited. Thermal shock to the tungsten causing small fragments to enter the weld pool is a common cause of tungsten inclusions and is the reason why modern power sources have a current slope-up device to minimise this risk.

This device allows the current to rise to the set value over a short period and so the tungsten is heated more slowly and gently. It is also used in the aerospace industry for such items as airframes and rocket motor cases. This means that the weld pool has a more favourable shape when it finally solidifies and crater cracking can be avoided. Using filler wires.

TIG is used for making high quality joints in heavier gauge pipe and tubing for the chemical. Modern power sources have a current slope-out device so that at the end of a weld when the welder switches off the current it reduces gradually and the weld pool gets smaller and shallower. The method is especially useful in welding the reactive metals with very stable oxides such as aluminium.

Shielding gas selection depends on the material being welded and the application. The process offers high productivity and is economical because the consumable wire is continuously fed. An arc is struck between the end of a wire electrode and the workpiece. A diagram of the process is shown in Figure 1. With automatic equipment. The weld pool is protected from the surrounding atmosphere by a shielding gas fed through a nozzle surrounding the wire.

In mechanised welding. In semi-automatic welding. The wire is fed through a copper contact tube also called a contact tip which conducts welding current into the wire. The wire is fed from a reel by a motor drive and the welder or machine moves the welding gun or torch along the joint line. Wires are generally produced in 0. The welding connections need to be checked for soundness.

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In dip transfer it also affects the rise of current and the overall heat input into the weld. The voltage will affect the type of transfer achievable. Because these additions react with the molten metal they are referred to as active gases and hence the name MAG welding metal active gas is the technical term that is used when referring to the welding of steels.

The use of a fully inert gas is the reason why the process is also called MIG welding metal inert gas and for precise use of terminology this name should only be used when referring to the welding of non-ferrous metals.

For non-ferrous metals and their alloys such as Al. This is usually either pure argon or an argon rich gas with a helium addition. For welding of steels — all grades.. Argon has a much lower ionisation potential and can sustain spray transfer above 24 welding volts. Argon-helium mixtures effectively give a hotter arc and so they are beneficial for welding thicker base materials.

CO2 gas is much cheaper than argon or its mixtures and is widely used for carbon and some low alloy steels. The addition of some helium to argon gives a more uniform heat concentration within the arc plasma and this affects the shape of the weld bead profile. Argon gives a very stable arc and little spatter. Ni and Cu an inert shielding gas must be used. Because of this high ionisation potential it gives very good penetration. Figure 5 Active shielding gas mixtures for MAG welding of carbon.

These quaternary mixtures permit higher welding speeds. A disadvantage is that when working in confined spaces. Welding grade inert gases should be downloadd rather than commercial purity to ensure good weld quality. The oxidising potential of the mixtures are kept to a minimum CO2-containing mixtures are sometimes avoided to eliminate potential carbon pick-up.

The density of argon is approximately 1. Argon Argon can be used for aluminium because there is sufficient surface oxide available to stabilise the arc. Because austenitic steels have a high thermal conductivity. For materials that are sensitive to oxygen. Blue is a cooler gas mixture. Light alloys aluminium magnesium. Some Ar-He mixtures containing up to 2.

Figure 6 Active shielding gas mixtures for MAG welding of stainless steels. Arc stability can be problematic in helium and argonhelium mixtures. There is a reduced risk of lack of fusion defects when using argon-helium mixtures. Helium mixtures require higher flow rates than argon shielding in order to provide the same gas protection. Ar-He gas mixtures will offset the high heat dissipation in material over about 3mm thickness.

Figure 7 Inert shielding gas mixtures for MIG welding of aluminium.

With globular-type transfer. Helium possesses a higher thermal conductivity than argon. High helium contents give a deep broad penetration profile. General-purpose gas: Substitution of helium for argon gives hotter arc.

General-purpose mixture: Higher heat input offsets high heat dissipation on thick sections. Spray transfer only. Good arc stability with minimum effect on corrosion resistance carbon pick-up. Titanium alloys require inert gas backing and trailing shields to prevent air contamination. Arc voltages V higher than Ar-CO2 mixtures. Good arc stability. High cost. Stiffer arc than Ar-CO2 mixtures.

This provides the experienced welder with a means of controlling the current during welding. Long electrode extensions can cause lack of penetration. The welding current required to melt the electrode at the required rate to match the wire feed speed reduces as the CTWD is increased.

Resistive heating depends on the resistivity of the electrode. The effect is therefore more pronounced for welding materials which have high resistivity. The electrode extension should be kept small when small diameter wires are being used to prevent excessive heating in the wire and avoid the resulting poor bead shape.

Contact tip Gas nozzle Contact tip setback Nozzle-to-work stand-off distance Electrode extension Arc length Contact tipto-work distance Workpiece Figure 10 Contact tip to workpiece distance. Increasing the electrode extension. The electrode extension should be checked when setting-up welding conditions or when fitting a new contact tube.

Normally measured from the contact tube to the workpiece Figure This can lead to spatter adherence and increased wear of the contact tube. The following gives suggested settings for the mode of metal transfer being used.

Joint access and type should also be considered when selecting the required gas nozzle and flow rate. The nozzle to work distance is typically mm. The nozzle diameter should be increased in relation to the size of the weld pool. Gas nozzles for dip transfer welding tend to be tapered at the outlet of the nozzle.

Nozzle sizes range from 13 to 22mm diameter. The flow rate must also be tuned to the nozzle diameter and shielding gas type to give sufficient weld pool coverage. If the CTWD is simultaneously reduced. Use of too small a nozzle may cause it to become obstructed by spatter more quickly and. Metal transfer mode Dip Spray Spray aluminium Contact tip position relative to nozzle 2mm inside to 2mm protruding mm inside mm inside 2. The arc current is flowing for the entire period of the drop detachment.

The droplet size equates to the wire diameter at the threshold level but decreases significantly as the welding current increases. The droplets detach from the tip of the wire and accelerate across the arc gap.

When the correct arc voltage to give spray transfer is used. The high welding current produces strong electromagnetic forces known as the pinch effect that cause the molten filament supporting the droplet to neck down. At very high currents wire feed speeds. The frequency at which the droplets detach increases with increasing current.

Above the transition current. This allows smooth. A typical pulse waveform and the main pulse welding variables are shown in Figure Pulse transfer uses pulses of current to fire a single globule of metal across the arc gap at a frequency of pulses. Pulse current and current density must be sufficiently high to ensure that spray transfer not globular always occurs so that positional welding can be used.

The pulse of current generates very high electromagnetic forces. A low background current typically A is supplied to maintain the arc. Pulse transfer is a development of spray transfer.

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Droplet detachment occurs during a high current pulse at current levels above the transition current level. Pulsing was introduced originally for control of metal transfer by imposing artificial cyclic operation on the arc system by applying alternately high and low currents. Before transfer occurs. To further minimise spatter levels. Gravity eventually detaches the globule when its weight overcomes surface tension forces.

Irregular droplet transfer and arc instability are inherent. Although the short-circuit is of very short duration. Globular transfer can only be used in the flat position and is often associated with lack of penetration.

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In globular transfer. There is a short duration short-circuit when the droplet contacts with the molten pool. During the short-circuit.

Increasing the inductance will also increase the arc time and decrease the frequency of shortcircuiting. The rapid rise in current to a high value would melt the shortcircuited electrode free with explosive force. If the constant voltage power supply responded instantly. Modern electronic power sources automatically set the inductance to give a smooth arc and metal transfer.

For each electrode feed rate. This magnetic field creates a current in the welding circuit that is in opposition to the welding current. Too little inductance results in excessive spatter. The current travelling through an inductance coil creates a magnetic field. Inductance is the property in an electrical circuit that slows down the rate of current rise Figure Figure 18 Relationship between inductance and current rise.

When MIG welding in the dip transfer mode. The higher the level of de-oxidants in the wire. A size of liner will generally fit 2 sizes of wire ie 0. Most steel wires are copper coated to maximise the transfer of current by contact between two copper surfaces at the contact tip but this also inhibits corrosion.

Quality of wire windings and increasing costs a Random wound. The level of de-oxidation of the wire is an important factor with single. Check that the liner is the correct type and size for the wire. Any loss of contact between the wire and contact tip will reduce the efficiency of current pick. The quality of the wire winding. Any excess pressure will deform the wire to an ovular shape.

The contact tip should be replaced regularly. Steel liners are used for steel wires and Teflon liners for aluminium wires. Correct extraction systems should be in use to avoid exposure to ozone and fumes. Typical welding imperfections: Any poor connection in the welding circuit will affect the nature and stability of the electric arc and is thus a major inspection point.

The cored wire consists of a metal sheath containing a granular flux. This flux can contain elements that would normally be used in MMA electrodes so the process has a very wide range of applications.

A check should always be made to ensure that the welder is qualified to weld the procedure being employed. Gas hose. Note that unlike MMA electrodes the potential hydrogen levels and mechanical properties of welds with rutile wires can equal those of the basic types.

Electrode wire to correct specification and diameter. Baking of cored wires is ineffective and will do nothing to restore the condition of a contaminated flux within a wire.

It would not have been found by any inspection method You are to oversee the arc. Shorter arc length can be obtained Tarek Abdel-Alim Cswip welding inspection notes and questions. Q:- What are the defects we can find in visual Inspection. MAY The course is ultimate for inspectors requiring homework for the CSWIP examinations to grow to be a welding inspector.

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