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 ID: 580402
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Slide1
Base Metal Preparation
Level 1 – Chapter 5Slide2
ObjectivesWhen 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 specificationSlide3
1.0.0 IntroductionTo 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 availableSlide4
2.0.0 Welding SafetyWelders 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 skinSlide5
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 ear plugs to protect ears from noise and sparksSlide6
3.0.0 Base Metal CleaningALL 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.Slide7
3.1.0 Surface CorrosionAll 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.Slide8
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
.Slide9
3.2.0 Defects Caused by Surface ContaminationSlide10
3.3.0 Mechanical CleaningMechanical cleaning is the most common method of removing surface contamination.
Tools used for mechanical cleaning include:
Hand tools
Power tools
SandblastingSlide11
3.3.1 Hand ToolsSome 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 steelSlide12
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 fileSlide13
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 anglesSlide14
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.Slide15
3.3.2 Power ToolsSlide16
3.3.2 Power ToolsSome common pneumatically powered tools:
Weld flux chippers
Needle scalers
Have about 18 to 20 blunt steel needles used for removing surface contamination
Chipping hammersSlide17
3.3.2 Power ToolsSlide18
4.0.0 Joint DesignWelded 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
costSlide19
4.1.0 Load ConsiderationsThe 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 offSlide20
4.2.0 Types of Joints
5 Types of joints:
Butt
Lap
Corner
T
Edge Slide21
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 drawingSlide22
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 wearSlide23
4.3.1 Surfacing WeldsSlide24
4.3.2 Plug and Slot WeldsPlug 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.Slide25
4.3.2 Plug and Slot WeldsSlide26
Break TimeTake a 15 min. breakSlide27
4.3.3 Fillet WeldsFillet 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.Slide28
4.3.4 Square Groove WeldsSquare 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.Slide29
4.3.4 Square Groove WeldsSlide30
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.Slide31
4.3.6 V-Groove WeldsTypically, 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.Slide32
3.3.5 V-Groove WeldsSlide33
4.3.7 Single vs. Double V-Groove Welds
The double V-groove require half the weld metal compared to the single V-groove.Slide34
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.Slide35
4.3.8 J- and U-Groove WeldsSlide36
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.Slide37
4.3.10 Groove Angles and Root OpeningsThe purpose of the groove angle is to allow access to the root of the weld.
The root preparation is sized to control melt-through.
Root faces are used with open joints but not when backing strips are used.Slide38
4.3.11 Open Root Welds
For open root welds on plate, the groove angle should be 60 degrees.Slide39
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)Slide40
4.3.12 Welds with Backing on PlateSlide41
4.4.0 Welding PositionIt 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.Slide42
4.5.0 Codes and WPSA 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.Slide43
4.5.0 Codes and WPSA WPS includes:
Welding parameters
Type of joint to used
Type of welding process
Groove designed
Groove preparation
Position of weld
Base material thickness rangeSlide44
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.Slide45
5.2.0 Mechanical Joint PreparationMechanical 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)Slide46
5.2.1 GrindersHand-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.Slide47
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.Slide48
5.2.2 Pipe Beveling MachinesSlide49
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.Slide50
5.3.0 Thermal Joint PreparationThermal 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.Slide51
5.3.0 Thermal Joint PreparationSpecial 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.Slide52
4.3.0 Thermal Joint PreparationSlide53
SummaryThe 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.Slide54
Answer review questions 1-15 on pg. 5.21Fill in trade terms 1-18 on pg. 5.23