cswip welding inspection notes and questions.pdf

Download CSWIP Welding Inspection notes and questions.pdf

Post on 03-Jan-2016

360 views

Category:

Documents

103 download

Embed Size (px)

DESCRIPTION

Welding Inspection notes and questions

TRANSCRIPT

  • CISWIP WI 3.1 Note (Produce By : Mohd. Aiman ) Page 1

    1

    WELDING INSPECTION - STEELS

    CONTENTS PAGE

    TERMINOLOGY 3

    THE DUTIES OF A WELDING INSPECTOR 9

    CODES AND STANDARDS 12

    THE WELDING PROCEDURE 14

    DESTRUCTIVE TESTING 20

    SYMBOLS 27

    MATERIALS 32

    FOUR FACTORS FOR ESTABLISHING A WELD 37

    WELDABILITY 38

    RESIDUAL STRESS AND DISTORTION 44

    HEAT TREATMENT 47

    CALIBRATION 49

    DEFECTS DETECTED BY SURFACE INSPECTION 50

    INTERNAL DEFECTS 54

    MACRO EXAMINATION 58

    NON-DESTRUCTIVE TESTING 61

    REPAIR BY WELDING 66

    CONSUMABLES 70

    WELDING POSITIONS 75

    WELDING PROCESSES

    MANUAL METAL ARC WELDING 78

    TUNGSTEN INERT GAS WELDING 83

    METAL INERT GAS WELDING 88

    SUBMERGED ARC WELDING 94

    AUTOMATIC METAL ARC WELDING 101

    ELECTRON BEAM WELDING 103

    ELECTRO-SLAG WELDING 105

  • CISWIP WI 3.1 Note (Produce By : Mohd. Aiman ) Page 2

    2

    TERMINOLOGY

    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.

  • CISWIP WI 3.1 Note (Produce By : Mohd. Aiman ) Page 3

    3

    TYPES OF JOINT

    The following are some typical joints:

    BUTT

    -----------------------------------------------------------------------------------------------------------

    TEE

    -----------------------------------------------------------------------------------------------------------

    CORNER

    -----------------------------------------------------------------------------------------------------------

    LAP

  • CISWIP WI 3.1 Note (Produce By : Mohd. Aiman ) Page 4

    4

    PLATE EDGE PREPARATION FOR BUTT WELDS

    The illustrations show standard terminology for the various features of plate edge preparations.

    Square edged closed butt Square edged open butt with backing strip

    3 mm sheet, 3 mm - plate (considerations - penetration control, backing strip of the same material and usually removed)

    Backing bar - ceramic or copper Fusible insert - electric bolt (e.b)

    (copper can cause loquation cracking) (uses TIG process)

    Single V Single bevel

    Double V Double bevel

    Single J Single U

    Double J Double U

  • CISWIP WI 3.1 Note (Produce By : Mohd. Aiman ) Page 5

    5

    included angle

    bevel angle

    bevel angle width

    sidewall

    face radius

    root face

    root gap land

    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.

  • CISWIP WI 3.1 Note (Produce By : Mohd. Aiman ) Page 6

    6

    Fillet welds have similar features.

    toes

    face

    fusion boundary

    root HAZ

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

    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 t2 t1 t2

    t1 t2 t1 t2

    t1 t2

    t1

    t2

  • CISWIP WI 3.1 Note (Produce By : Mohd. Aiman ) Page 7

    7

    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

    l t1 = t2 t1 t1 t1 t1

    t2 t2

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

    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

  • CISWIP WI 3.1 Note (Produce By : Mohd. Aiman ) Page 8

    8

    THE DUTIES OF THE WELDING INSPECTOR

    VISUAL 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.

    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

Recommended

View more >