DEFINITION OF WELDING

DEFINITION OF WELDING

• WELDING is a process used to joint Metals by the application of heat, pressure or a combination of both.

• ARC WELDING that used an electric arc to provide heat.

• WELDABILITY is the feasibility of welding particular metal or alloy. A number of factors affect weld ability  including chemistry, surfaces, finish, heat treating tendencies, etc

• CARBON EQUIVALENT (CE) is measure of the weld ability of the steel.

• HAZ is the area between the parent materials and weld that under goes micro structure changes due to the influence of the welding process.

• PREHEAT is heating prior to welding to control the cooling rate.

• PWHA is heat treatment after welding for stress relief.

TYPE OF MATERIAL

1. Carbon Steel 2.Stainless Steel  3. Duplex Stainless Steel  4. Cunni 5. Inconel etc

WHAT IS DIFECT

Defect is a flaw or flaws that by nature or accumulated effect render a part of product unable to meet minimum applicable acceptance standard or applications. The term designates reject ability.

WHAT IS DISCONTINUITY

Discontinuity is an interruption of the typical structure of a material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics. A discontinuity is not necessarily a defect.

WELDING DEFECT

A.  Hydrogen / Cold Cracking cause: 1. High Hydrogen Level 2. Brittle Structure 3. High Stress

Avoidance

·         Preheat

·         Proper cleaning on area to be welded

·         Apply low Hydrogen Welding Process

·         Used Austenitic  or Nickel Filler Materials

·         Ensure good Fit-Up

·         PWHT

·         Avoid Poor Weld Profile

·         Use low Hydrogen Electrode

2. Solidification / Hot Cracking cause: 1. High Level of Impurities in Weld/Parent Metal 2. Poor cleanliness 3. High Level Restraint 4. Insufficient Weld beat size or sharp.

Avoidance

·         Use of High Mn and Low C Filler Metal

·         Use Low Dilution Welding Process

·         Use High Quality Parent Metal

·         Clean Joint Preparation

·         Joint Design selection Dept to Width Ratio

3. Porosity cause: 1. Moisture in Electrode / Shielding Gas 2. Contamination / Poor Cleanliness 3. Inappropriate Gas low rate, Long Arc length 4. High Solidification Rate

Avoidance

·         Reduce Moisture

·         Proper Cleaning

·         Correctly Gas Plow Rate and Welding Technique

·         Apply Preheat

4. Lamellar Tearing cause : 1. High level of through-thickness stress (Joint Design) 2.Presence of Elongated non Metallic inclusion on the Parent Materials

Avoidance

·         Buttering with low strength on ductile weld metal

·         Modified Joint Design

·         Used Materials with good Through Thickness Properties (TTP)

·          

REPAIRS TO CRACK

1.    Determine the cause

2.    Correct the problem

3.    Take precautions to prevent  reoccurrence

4.    Generally required to repair using the smaller electrode.

5. Under Cut Definition: A Groove cut at the toe of the weld and left unfilled.

6. ARC Strikes Definition: Localized coalescence outside the weld zone creates hard and brittle zones.

7. Misalignment Hi-Lo Definition: A mount of joint is out of alignment at the root.

8. Spatter Definition: Small particles of weld metal  expelled from the welding operation which adhere to the base  Metal surface

I.   Tungsten Inclusion Definition: A tungsten particle embedded in a weld (typically GTAW only)