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    Cracks in Welds

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    jesycuban
    This document discusses cracks in welds, including the different types of cracks and factors that promote them. It summarizes that there are two main types of cracks: hot cracks that occur during solidification while the weld metal is partially solidified, and cold cracks that occur after solidification when hydrogen embrittlement causes cracking. The document outlines various factors that can promote each type of crack, such as solidification structure, hydrogen content, thermal stresses, and material composition. It also categorizes cracks based on their location, such as weld metal cracks, base metal cracks, and cracks along the fusion line. Techniques for preventing cracking include preheating, post-heating, reducing stresses, and using low-hydrogen electrodes.

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    Cracks in Welds

    Uploaded by

    jesycuban
    339 views19 pages
    This document discusses cracks in welds, including the different types of cracks and factors that promote them. It summarizes that there are two main types of cracks: hot cracks that occur during solidification while the weld metal is partially solidified, and cold cracks that occur after solidification when hydrogen embrittlement causes cracking. The document outlines various factors that can promote each type of crack, such as solidification structure, hydrogen content, thermal stresses, and material composition. It also categorizes cracks based on their location, such as weld metal cracks, base metal cracks, and cracks along the fusion line. Techniques for preventing cracking include preheating, post-heating, reducing stresses, and using low-hydrogen electrodes.

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    This document discusses cracks in welds, including the different types of cracks and factors that promote them. It summarizes that there are two main types of cracks: hot cracks that occur during solidification while the weld metal is partially solidified, and cold cracks that occur after solidification when hydrogen embrittlement causes cracking. The document outlines various factors that can promote each type of crack, such as solidification structure, hydrogen content, thermal stresses, and material composition. It also categorizes cracks based on their location, such as weld metal cracks, base metal cracks, and cracks along the fusion line. Techniques for preventing cracking include preheating, post-heating, reducing stresses, and using low-hydrogen electrodes.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    339 views19 pages

    Cracks in Welds

    Uploaded by

    jesycuban
    This document discusses cracks in welds, including the different types of cracks and factors that promote them. It summarizes that there are two main types of cracks: hot cracks that occur during solidification while the weld metal is partially solidified, and cold cracks that occur after solidification when hydrogen embrittlement causes cracking. The document outlines various factors that can promote each type of crack, such as solidification structure, hydrogen content, thermal stresses, and material composition. It also categorizes cracks based on their location, such as weld metal cracks, base metal cracks, and cracks along the fusion line. Techniques for preventing cracking include preheating, post-heating, reducing stresses, and using low-hydrogen electrodes.

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    CRACKS IN WELDS

    PAPER PRESENTATION

    Introduction
    Crack is a discontinuity caused by the tearing of the metal while in a plastic condition or fracturing of the metal when cold. Cracks occur because the stress at that point in the weldment exceeds the ultimate tensile strength or ultimate shear strength of the base metal or weld metal. Cracking can occur in the weldment, at the fusion line or in the base metal. Cracks may be classified according to location and direction of line and they may range in size from large cracks to extremely small fissures. Mainly weld cracking are of two 2 types: 1) Hot Cracks, 2) Cold Cracks

    Hot Cracks

    Hot-cracks takes place when the weld metal is half liquid and half solid and has no tensile strength. In another way they occur during solidification. Hot cracks occur mainly in the weld bead but sometimes they may develop in the HAZ ( Heat Affected Zone ). When cracks are located in the weld metal they are referred to as solidification cracks while in HAZ they are called liquation cracks.

    Factors Which May Promote Hot Cracking


    Solidification Structure Segregation High Stress in Weld Metal Material Thickness Joint Restraint Width/Depth Ratio Weld Bead Shape Material Composition; high Carbon and Nickel Contents Weld Procedure: 1) High Welding Speed, 2) Long Arc Poor Fit-up

    Cold Cracking

    Cold cracking occur when HAZ of the base metal becomes hard and brittle due to its rapid cooling after the weld metal has been deposited and sufficient hydrogen has been absorbed by weld metal from the arc atmosphere. The martensite formation temperature, Ms is relatively low HIC tends to occur at relatively low temperatures and hence the name cold cracking.
    COLD CRACK (HIC) IN HAZ
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    Factors Which may Promote Cold Cracking

    Hydrogen in weld metal and HAZ Joint restraint and high thermal severity Presence of impurities Susceptible microstructure of HAZ High welding speeds Low welding density Weld of insufficient cross-sectional area Relatively low temperature, between 200 and 100 C
    6

    Nomenclature, Location & Orientation of Weld Cracks

    Longitudinal cracks
    Transverse cracks Crater Cracks Underbead Cracks Toe Cracks All these kinds of cracks are classify in the weld metal and HAZ (Base Metal).
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    Classification of Cracking According to Location in a Weldment

    1)weld-metal crater cracking; 2)weld-metal transverse cracking; 3)Base metal heat-affected zone transverse cracking; 4) Weld-metal longitudinal cracking; 5)Toe cracking; 6)Underbead cracking; 7)Fusion line cracking; 8)Weld-metal root cracking
    8

    Weld Metal Cracks

    Crater cracks:- Crater cracks can occur when welding is interrupted. These cracks are usually star shaped and progress only up to the edge of the crater. Such cracks are also called Paw Cracks for their resemblance to birds paw. Longitudinal Weld Metal Cracks:- Longitudinal weld metal crack usually running through the centre of the weld, often is an extension of crater formed at the end of the weldment.

    Weld Metal Cracks

    Transverse Weld Metal Cracks:- Transverse weld metal cracks that


    run across the weld perpendicular to weld axis. These are often shrinkage cracks produced when the weld metal is cooling and contracts.

    LONGITUDINAL WELD METAL CRACKS

    TRANSVERSE WELD METAL CRACKS


    10

    Base Metal Cracks

    Longitudinal Base Metal Cracks:- This type of cracks run parallel to the weld but lie in base metal and may be formed as extensions of bond-line cracks due to poor weld metal penetration into the sides of the butt joint. Transverse Base-Metal Cracks:- Transverse base metal cracks develop perpendicular to weld axis and are placed in the HAZ. They are usually associated with welding of high hardenability steels e.g., tool steels and certain alloy steels.

    LONGITUDINAL BASE METALCRACK


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    Base Metal Cracks

    Underbead or Toe Cracks:- Surface Cracks in te base metal,under or near the weld are known as underbead cracks. Similar cracks that appear on the plate surface adjacent to the weld are called toe cracks.

    TRANSVERSE BASE METAL CRACKS

    UNDERBEAD & TOE CRACKS

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    Factors Contributing to Weld Metal Cracking

    The contraction forces set up in the weld metal on cooling tend to cause cracking in the weld metal and the base metal. The susceptibility to cold cracking is proportional to he hydrogen content of the weld atmosphere. With an open arc and hot humid weather the arc atmosphere will contain more hydrogen as water vapour then in cool, dry weather which causes cold cracking.

    HIC IN ROOT BEAD OF A YGROOVE

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    Factors Contributing to Weld Metal Cracking

    Low heat input with interruption in the welding cycle tends to aggravate the cracking problem. The welding position and its influence on bead size, heat input, number of passes, etc. has a direct influence on the cracking tendency. Greater crack sensitivity is exhibited by high-alloy base metal and heavier plate thickness.
    14

    Hot Cracking Tests

    For determining hot cracking propensity of metals, the most sensitive tests are:

    1.

    Varestraint test FISCO Test Lehigh Restraint Test

    2.

    3.

    4.

    Tekken Y-Groove

    15

    Cold Cracking Tests

    1.

    These are also referred to as Hydrogen-Induced Cracking Tests & Weldability tests. The most commonly used tests are: Cruciform Test Controlled Thermal Severity (CTS) Test Lehigh Restraint Test Implant Test
    16

    2.

    3.

    4.

    Techniques for Avoid Cracking

    Dry the electrodes or the flux in accordance with the manufacturers recommendations. Reduce stresses on the weld by avoiding large root gaps and high restraint.

    If preheating is specified in the welding procedure, it should also be applied when tacking or using temporary attachments.
    Preheat the joint to a distance from the joint line to ensure uniform heating through the thickness of the material. Adhere to the heat input requirements.
    17

    Techniques for Avoid Cracking

    post heat for approximately two to four hours after welding depending on crack sensitivity. In situations where adequate preheating is impracticable, or cracking cannot be avoided, austenitic electrodes may be used. clean the joint faces and remove contaminants such as paint, cutting oils, grease.

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    THANK YOU
    Prepared By: JIGAR MEVADA

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