Base Metal Preparation Level 1 Chapter 5 Objectives

Base Metal Preparation Level 1 – Chapter 5

Objectives � When we have completed this chapter, you should be able to : › › Clean base metal for welding and cutting Identify and explain joint design Mechanically and thermally bevel steel plate Select joint design based on a welding procedure specification

1. 0. 0 Introduction To ensure that the highest quality welds are produced and to comply with codes, base metals must be properly prepared prior to welding. � The type of preparation required depends on: � › › › The governing code requirements Base metal type Condition of base metal Welding process to be used Equipment available

2. 0. 0 Welding Safety � Welders routinely use manual and powered tools to clean and shape metals. � Metal particles ground from the work pieces are usually hot, and will burn your skin

2. 1. 0 Protective Clothing and Equipment To maintain safety and prevent injury, it is essential that you wear the appropriate protective clothing and equipment when preparing metals. � Follow these guidelines: � › › Always wear safety glasses Wear proper leather or fire retardant clothing Wear safety boots Wear plugs to protect ears from noise and sparks

3. 0. 0 Base Metal Cleaning � ALL base metal should be cleaned before welding. � To ensure quality welds and to conform to code requirements, surface contaminants and oxides must be removed prior to welding.

3. 1. 0 Surface Corrosion � � � All metal has surface corrosion. Corrosion occurs when metal is exposed to air. Some corrosion exist as a thin film that merely stains the metal. A very course type of corrosion that is found on carbon steel is rust. Alloys steel is mild steel that has had chromium and/or copper added to protect it from corrosion. Weathering steel is an example of copper alloy steel that protects itself form corrosion.

3. 2. 0 Defects Caused by Surface Contamination The most common defect caused by surface contamination is porosity. � Porosity occurs when gas pockets or voids appear in the weld metal. � The gas pocket is trapped as the weld metal solidifies, but as the next layer of weld is deposited, the porosity continues to float up. � When the porosity has a length greater than its width it is called piping porosity. �

3. 2. 0 Defects Caused by Surface Contamination

3. 3. 0 Mechanical Cleaning � Mechanical cleaning is the most common method of removing surface contamination. � Tools used for mechanical cleaning include: › Hand tools › Power tools › Sandblasting

3. 3. 1 Hand Tools � Some common hand tools are: › Scrapers �Used to remove dirt, grease, and paint › Wire brushes �Brushes will remove paint and light to medium surface corrosion. (do not remove tight corrosion) �Only stainless brushes should be used when working with aluminum or stainless steel

3. 3. 1 Hand Tools � Some common hand tools are: › Files �Remove surface corrosion �Be sure there is a handle on the file tang �Tang – pointed end of file

3. 3. 2 Power Tools � For larger jobs or jobs where speed is important, power tools are best. � Power tools may be electrically or pneumatically powered. � Some common power tools are: › Angle grinders / End grinders �Are very effective in removing large areas of surface contamination. › Die grinders / Small angle grinders �Work well for weld grooves and bevel angles

3. 3. 2 Power Tools � Grinders have attachments for special applications: › › › Grinding disc Rotary files Flapper wheels Cut off wheels Wire wheels �Use only stainless steel wire brush attachments when working on stainless steel or aluminum.

3. 3. 2 Power Tools

3. 3. 2 Power Tools � Some common pneumatically powered tools: › Weld flux chippers › Needle scalers �Have about 18 to 20 blunt steel needles used for removing surface contamination › Chipping hammers

3. 3. 2 Power Tools

4. 0. 0 Joint Design � Welded joints are selected primarily for the safety and strength required for the conditions to be encountered. � When selecting the joint many factors must be taken into account: › › › Load considerations The environment Materials Processes cost

4. 1. 0 Load Considerations � The weld joint must be designed to withstand the stresses caused by the loads. � Load types: › Tensile – capable of being stretched › Compression – the reduction of volume or mass › Bending – to make curved › Torsion – twisting › Shear – to cut off

4. 2. 0 Types of Joints 5 Types of joints: �Butt �Lap �Corner �T �Edge

4. 3. 0 Types of Welds Most types of welds require some degree of base metal edge preparation. � Common types of welds: � › › › › � Surfacing Plug Fillet Square bevel Bevel groove V-groove J and U groove If a particular type of weld requires a specified root opening, it is shown on the welding drawing

4. 3. 1 Surfacing Welds � Surfacing welds are used to build up a base surface that has become worn below the desired thickness. � Before applying the first layer, the base metal should be cleaned to remove contaminations. � Surfacing is used to: › Rebuild expensive tool and die parts › Repair heavy equipment that has wear

4. 3. 1 Surfacing Welds

4. 3. 2 Plug and Slot Welds � Plug and slot used to join metal pieces when the edges cannot be welded. � The plug or slot weld may be applied: › Lap › Corner › T – joints � Preparation of the base metals for plug/slot welds requires proper cleaning of both pieces, then drilling of the hole.

4. 3. 2 Plug and Slot Welds

Break Time � Take a 15 min. break

4. 3. 3 Fillet Welds � Fillet welds may be applied to lap, T-, or corner joints. � Fillet welds only require removal of contaminants from the base metal with little or no joint edge preparation.

4. 3. 4 Square Groove Welds � Square groove welds can be used with butt joints, corner joints, T joints and edge joints. � The difference between the fillet and square groove is that a square groove requires a root opening between the two base pieces prior to welding. � This allows greater penetration into a greater portion of the joint.

4. 3. 4 Square Groove Welds

4. 3. 5 Bevel-Groove Welds � Bevel grooves provide greater surface penetration than the square groove. � A bevel groove weld preparation may include a specified root opening along with a bevel cut.

4. 3. 6 V-Groove Welds � Typically, a 45 degree angle will be cut on both edges of the base metal. � The angle may not extend from the top of the bevel edge to the bottom of the bevel edge on each piece. � The flat surface from where the angle stops to the bottom of the piece is called the root face.

3. 3. 5 V-Groove Welds

4. 3. 7 Single vs. Double V-Groove Welds � The double V-groove require half the weld metal compared to the single V-groove.

4. 3. 8 J- and U-Groove Welds � J-groove weld requires only one base metal member to have its edge grooved in the shape of a J. � A U-groove is formed by preparing two matching J-grooves on the base metal members.

4. 3. 8 J- and U-Groove Welds

4. 3. 9 Combination Fillet & Groove Welds � The combination weld requires more preparation time than a fillet weld alone, but saves time and material and helps reduce distortion.

4. 3. 10 Groove Angles and Root Openings � The purpose of the groove angle is to allow access to the root of the weld. � The root preparation is sized to control meltthrough. � Root faces are used with open joints but not when backing strips are used.

4. 3. 11 Open Root Welds � For open root welds on plate, the groove angle should be 60 degrees.

4. 3. 12 Welds with Backing on Plate � Backing for plate can be: › Stripes made from the same material as the base metal �The recommendation for a backing strip for welding mild steel up to ¾” thick is 3/8” thick by 3” wide. (bottom of pg 5. 15) › › � Flux-coated tape Fiberglass –coated tape Ceramic tape Gas Check the WPS for joint preparation before using flux-tape, fiberglass coated, or ceramic tape. (note pg 5. 15)

4. 3. 12 Welds with Backing on Plate

4. 4. 0 Welding Position It is easier and faster to weld groove welds in the flat position and fillers in the flat or horizontal position than it is to weld out of position. � Always try to position the weldment so that welding is performed in the flat position. � When welding pipe, weld as many fittings as possible before taking the pipe into position, try to leave the welds that will be the most accessible and easiest to perform for last. �

4. 5. 0 Codes and WPS �A welding code is a detailed listing of the rules and principles that apply to specific welded products. � A weld procedure specification (WPS) is a written set of instructions for producing reliable welds.

4. 5. 0 Codes and WPS �A › › › › WPS includes: Welding parameters Type of joint to used Type of welding process Groove designed Groove preparation Position of weld Base material thickness range

5. 0. 0 Welding Joint Preparation � There are two ways to prepare a joint: › Mechanically using: �Nibblers �Grinders �Cutters › Thermally using: �Oxyfuel cutting �Plasma arc �Carbon arc � Type of method to used depends on the type of metal and specifications.

5. 2. 0 Mechanical Joint Preparation � Mechanical joint preparation is used most often on alloy steels and nonferrous metal. � It is slower than thermal methods. � Advantages: › High precision with low heat › Absence of oxides (slag)

5. 2. 1 Grinders � Hand-held electric or air-operated grinders are used in welding shops and even more often in the field to prepare pipe and plate for welding.

5. 2. 2 Pipe Beveling Machines � Nearly every piece of pipe that is welded requires that the edge be cut square and beveled according to specifications. � Mechanically cutting and beveling is often accomplished by using electrically or pneumatically powered beveling machines. � Various models are available to cut and bevel 2” to 60” pipe.

5. 2. 2 Pipe Beveling Machines

5. 2. 3 Nibblers and Cutters � Nibblers prepare the edge of a plate or pipe with a reciprocal punch that cuts off a chip with each stroke. � Nibblers must have access to an edge to be used. � Cutters use round cutting tools similar to mill cutting tools › Cutters leave the surface much smoother than nibblers. � Cutters made for pipe are sometimes called pipe-end-prep machines.

5. 3. 0 Thermal Joint Preparation � Thermal joint preparation includes preparing a joint with the oxyfuel, plasma arc, or carbon arc. � The carbon arc process is best for gouging seams, crack, or weld repairs. � The torch for oxyfuel or plasma cutting can be hand held or mounted on a motorized carriage.

5. 3. 0 Thermal Joint Preparation � Special equipment is used for cutting pipe. � A steel ring or special chain with rollers is attached to the outside of the pipe. � For large diameter pipe (54” or larger), special equipment is available. � The torch mechanism is mounted on the inside or outside of pipe.

4. 3. 0 Thermal Joint Preparation

Summary � The importance of proper joint preparation cannot be overemphasized. � If a joint is not properly prepared, the resulting weld will not perform as designed. � It is important to select the proper type of joint and use proper joint preparation methods to ensure acceptable welds. � Welding codes set guidelines that must be followed during joint preparation.

� Answer review questions 1 -15 on pg. 5. 21 � Fill in trade terms 1 -18 on pg. 5. 23