CSWIP 3.1 Welding Inspection Notes

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WELDING INSPECTION - STEELS CONTENTSTERMINOLOGY THE DUTIES OF A WELDING INSPECTOR CODES AND STANDARDS THE WELDING PROCEDURE DESTRUCTIVE TESTING SYMBOLS MATERIALS FOUR FACTORS FOR ESTABLISHING A WELD 37 WELDABILITY RESIDUAL STRESS AND DISTORTION HEAT TREATMENT 47 CALIBRATION DEFECTS DETECTED BY SURFACE INSPECTION INTERNAL DEFECTS MACRO EXAMINATION NON-DESTRUCTIVE TESTING REPAIR BY WELDING CONSUMABLES WELDING POSITIONS 49 50 54 58 61 66 70 75 38 44 PAGE 3 9 12 14 20 27 32

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WELDING PROCESSES1

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MANUAL METAL ARC WELDING TUNGSTEN INERT GAS WELDING METAL INERT GAS WELDING SUBMERGED ARC WELDING AUTOMATIC METAL ARC 101 ELECTRON BEAM WELDING ELECTRO-SLAG WELDING WELDING

78 83 88 94

103 105

TERMINOLOGY2

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Use of the correct terminology is important. CSWIP uses BS 499 standard. Frequently the terms weld and joint are used incorrectly. Exact definitions are given in BS 499 PT 1 1983 Welding terminology and BS 499 Pt 2: 1980 Weld symbols. TYPES OF WELD Butt Weld

Fillet Weld

Edge Weld

small indentations at each weld

Spot Weld (Illustration depicts resistance weld. Spot welds can be made with MIG or TIG processes.)

The four basic welds can be used to join various types of joints.

TYPES OF JOINT The following are some typical joints:

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4

BUTT

----------------------------------------------------------------------------------------------------------TEE

----------------------------------------------------------------------------------------------------------CORNER

----------------------------------------------------------------------------------------------------------LAP

PLATE EDGE PREPARATION FOR BUTT WELDS The illustrations show standard terminology for the various features of plate edge preparations.

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Square edged closed butt < 3 mm sheet, > 3 mm - plate removed)

Square edged open butt with backing strip (considerations - penetration control, backing strip of the same material and usually

Backing bar - ceramic or copper (copper can cause loquation cracking)

Fusible insert - electric bolt (e.b) (uses TIG process)

Single V

Single bevel

Double V

Double bevel

Single J

Single U

Double J

Double U

included angle bevel angle sidewall face root gap root face bevel angle width radius land 5

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FEATURES OF A COMPLETED WELD A butt weld in plate, made by welding from both sides, has two weld faces and four toes. In a full penetration weld made from one side, the protruding weld on the underside is called the penetration bead, which also has two toes. The root is defined (BS 499) as the zone on the side of the first run farthest from the welder. toe face toe

root toe face toe

If a weld is sectioned, polished and etched, the fusion boundary can be established. Metal lying between the two fusion boundaries is weld metal - a mixture of deposited metal and plate metal that has been melted. The fusion zone is the area of highest dilution between filler metal and parent plate. Adjacent to the fusion boundary is the heat affected zone (HAZ), in which the plate material has had its metallurgical structure modified by the heat of welding. excess weld metal fusion zone throat fusion boundary / line

HAZ Excess weld metal is the correct term, not weld reinforcement. Excess weld metal lying outside the plane joining the toes of the weld. Fillet welds have similar features. toes face fusion boundary root HAZ

The shape of a fillet in cross-section is described in three terms.6

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Mitre fillet

Convex fillet

Concave fillet

A convex fillet has a poor toe blend - greater notch effect and sharper angle at toe, not used in fatigue situations. A concave fillet has a better toe blend for fatigue situations, however a reduced throat. The concave weld may be made by welding alone or by subsequent grinding. SIZE OF WELDS Full Penetration Butt Welds. The general rules are: design throat thickness = thickness of the thinner part joined. cap width = prep width + 10% either side (for open prep, not specified in BS 499) Partial Penetration Butt Welds. The term partial penetration strictly implies butt welds that are designed to have less than full penetration. Failure to achieve full penetration when it is wanted should be listed as the defect incomplete penetration. The design throat thickness of a partial penetration weld is t1 and the actual throat thickness is t2. With a partial penetration weld made from both sides, the design throat thickness is t1 + t1 and the actual throat thickness is t2 + t2. Note that the degree of penetration must be known. t1 t1 t2 t2 t1 t1 t1 t1 t2 Fillet Welds. Fillet weld sizes are calculated by reference to allowable shear stress on the throat area, i.e. throat area = design throat thickness x length of weld. The size required is specified on drawings in terms of leg length (l). For fillet welds with equal leg lengths l = 1.4 t1. This does not apply to concave fillet welds. l t2 t2 t2

l

t1 = t2

t1 t2

t1 t2

t1

t1

If an asymmetrical weld is required, both leg lengths are specified and t1 is taken as the minimum throat dimension.7

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l1 l2 t1 Deep penetration fillet weld. With high current density processes, e.g. submerged arc and MIG (spray), penetration along the joint line can be produced. This gives an increase in throat thickness with no change in leg length.

l l t1 t1

THE DUTIES OF THE WELDING INSPECTORVISUAL INSPECTION At any point in the course of welding, i.e. tacking, root pass, filler pass or capping pass, but particularly for the root and cap, a detailed inspection may be required. British Standard 5289: 1976 gives guidance on tools and responsibilities together with sketches of typical defects. The inspector at this point must a) observe, identify and perhaps record (measure) the features of the weld. b) decide whether the weld is acceptable in terms of the particular levels that are permitted; defect levels may be in-house or national codes of practice. When the defect size is in excess of the permitted level then either a concession must be applied for (from a competent person), or the weld rejected. AIDS OF VISUAL INSPECTION Illumination: Good lighting is essential. Inspection Lenses: The magnification should not exceed 2 - 2.5 diameters. If higher magnification is required use a binocular microscope. Optical viewing can progressively develop from eyesight, to use of a hand torch and mirror, to the addition of a magnifier and light source.8

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In order to achieve accessibility, remote probe units are available which must have the following properties. a) Large field of vision b) Freedom from distortion of image c) Accurate preservation of colour values d) Adequacy of illumination CODE OF PRACTICE A code of practice for an inspection department should take the form outlined below. It is appreciated that full implementation of the code would be extremely costly and therefore it may be necessary to reduce the amount of inspection to less than is theoretically required. The inspector should be familiar with the following: a) All applicable documents b) Workmanship standards c) All phases of good workshop practice d) Tools and measuring devices INSPECTION BEFORE WELDING Before Assembly: Check * All applicable documents. * Quality plan is authorised and endorsed with signature, date and company stamp. * Application standard is up to date with the latest edition, revision or amendment. * The drawings are clear, the issue number is marked and the latest revision is used. * Welding procedure sheets (specifications) are available, have been approved and are employed in production. * Welder qualifications with identification and range of approval are verified and that only approved welders as required are employed in production. * Calibration certificates, material certificates (mill sheets) and consumer certificates are available and valid. * Parent material identification is verified against documentation and markings. * Material composition, type and condition. * Correct methods are applied for cutting and machining. * Identification of welding consumables such as electrodes, filler wire, fluxes, shielding and backing gases and any special requirements (e.g. drying) are met. * Plant and equipment are in a safe condition and adequate for the job. * Safety permits e.g. hot work permit, gas free permit, enclosed space certificate are available and valid. After Assembly Check * Dimensions, tolerances, preparation, fit-up and alignment are in accordance with the Approved drawings and standards. * Tack welds, bridging pieces, clamping and type of backing - if any used are correct. * Cleanliness of work area is maintained. * Preheat in accordance with procedure. NOTE Good inspection prior to welding can eliminate conditions that lead to the formation of defects. INSPECTION DURING WELDING9

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Check * The welding process must be monitored. * Preheat and interpass temperatures must be monitored. * Interpass cleaning - chipping, grinding, gouging, must be monitored. * Root and subsequent run sequence. * Essential variables such as current, voltage, travel speed to be monitored. * Filler metals, fluxes and shielding gases are correct. * Welding is in compliance with weld procedure sheet and application standard. INSPECTION AFTER WELDING Check * Visual inspection to be carried out to ascertain acceptability of appearance of welds. * Dimensional accuracy to be ascertained. * Conformity with drawings and standards requirements. * Post weld heat treatment, if any, monitored and recorded. * NDT carried out and reports assessed. * Assess def