Joint Fit-UP & alignment Level 1 Chapter 10

Objective When we have completed this chapter, you will be able to: Identify and explain job code specifications Use fit-up gauges and measuring devices Identify and explain distortion Fit up joints using plate and pipe fit-up tools Check for joint alignment

1.0.0 Introduction Joint design and setup affect the safety and quality of completed weldment. Because joint design and setup are so important, they are covered by written codes and specifications that must be followed. Special tools to measure and aid fit-up are also available.

2.0.0 Job Code Specifications Whenever a bridge, building, ship or pressure vessel is welded, the manufacturer and the buyer must reach agreement on how each weld will be made. To eliminate the need to write a new code for each job, government agencies, societies, and associations have developed codes. These codes are used universally to ensure safety and quality when welds are made.

2.1.0 Governing Codes and Standards A welding code or standard is a detailed listing of the rules and principles that apply to specific welded products. Codes ensure that safe and reliable welded products will be produced and that persons associated with the welding operation will be safe.

2.1.0 Governing Codes and Standards In addition, when codes are specified, the use of these codes is mandated with the force of law by one or more government jurisdictions. Here are some of the more common codes and standards: API 1104-Standards for Welding of Pipeline and Related Facilities- used for pipelines ASME Boiler and Pressure Vessel Code – American Society of Mechanical Engineers ASME B31.1, Power Piping – used for pressure piping AWS D1.1 – Structural Welding Code – Steel

2.2.0 Code Changes Codes are periodically reviewed and updated. Addendum sheets (new pages) for the areas of the code affected by the changes are issued. The ASME issues yearly addendums. The yearly addendum is identified by placing the letter A in front of the year on the cover of the code.

2.3.0 Welding Procedure Specifications (WPS) A welding procedure specification is a written set of instructions for producing sound welds. Each WPS is written and tested in accordance with a particular welding code or specification and must be in accordance with industry practice. If a weld does require a WPS, the WPS must be followed. Consequences for not following a required WPS are unsafe weldment that could endanger life, rejection of the weldment and lawsuits.

2.3.0 Welding Procedure Specifications (WPS)

2.3.0 Welding Procedure Specifications (WPS) The requirement for the use of a WPS is often listed on job blueprints as a note or in the tail of the welding symbols. It is the responsibility of each manufacturer or contractor to test and qualify the WPS before using it. The WPS is tested by welding test coupons. Then, the coupons are tested according to the code.

2.3.0 Welding Procedure Specifications (WPS) The testing includes nondestructive testing (NDT), tensile strength tests, and root, face, or side bends tests. The results of the testing are recorded on a procedure qualification record (PQR). The WPS and PQR must be kept on file.

2.3.0 Welding Procedure Specifications (WPS) Information typically found on a WPS includes: Base metal-the chemical composition of the base metal using the standard identification. Example – A36 – carbon steel Welding process Filler Metal Type of Current Arc voltage and travel speed Joint design Joint preparation Positions of welding

3.0.0 Fit-Up Gauges and Measuring Devices Before making a weld, the joint must be fit up and checked to ensure it conforms to the WPS. The most common tools used to lay out and check joint fit-ups are straightedges, squares, levels and Hi-lo gauges.

3.1.0 Straightedges Straightedges are used to mark straight lines and check joint alignment. Many have calibrations along their length for measuring. Straightedges, particularly longer ones, are typically fabricated on the job from small channel or angle iron.

3.2.0 Squares Two types of squares are used for layout: pipefitter’s square and a combination square. Pipefitter’s square is used to measure angles and check squareness. Combination squares are smaller with blades typically 12” or 18” long. They have replaceable attachments that slide along the blade.

3.2.0 Squares

3.2.0 Squares Attachments include a combination 90 degree / 45 degree level head, a centering head, and a protractor head. The combination attachment is used to check and lay out 90 degree and 45 degree angles, to check level, and to measure depth. The centering head is used to measure round stock and to locate the center of shafts or other round objects. The protractor is used to lay out and check angles.

3.3.0 Levels Levels come in a variety of sizes and shapes. Some have magnetized bases. Levels are used to check that layouts are level (horizontal) and plumb (vertical). Levels use a bubble in a glass vial to check level and plumb. Centering the bubble between the lines marked on the vial indicates level or plumb. Some levels have a 45 degree vial.

3.3.0 Levels

3.4.0 Hi-Lo Gauges The primary purpose of a Hi-Lo gauge is to check for pipe joint misalignment. The name of the gauge comes from the relationship between the alignment of one pipe to the other pipe, which is called high-low.

3.4.0 Hi-Lo Gauges

3.4.1 Internal Misalignment Checks To check for internal misalignment, Hi-Lo gauges have two prongs that are pulled tightly against the inside diameter of the joint so that one prong is flush with each side of the joint. The variation between the two stops is read on a scale marked on the gauge.

3.4.1 Internal Misalignment Checks Many HI-Lo gauges also have the capability to check the following: Pipe wall thickness Root opening Weld reinforcement

4.1.0 Positioning Parts of a Weldment Hydraulic jacks, chain falls, and come alongs are used to position parts of a weldment. Hydraulic Jacks Never weld directly on the hydraulic jack base or ram. Monitor the jack for oil leaks.

4.1.2 Chain Hosts Chain hosts, also called chain falls, are used to lift or lower weldment parts. Secure the chain hoist over the weldment with an approved sling wrapped around a structural member. Never hang chain hosts from any item not designed to carry external loads.

4.1.3 Come-Alongs Come-alongs can be used for vertical lifting and pulling at angles. More than one come-along or chain fall can be used to precisely position a weldment. Before welding, make use the welding current will not pass through the come-along.

Chain Hoist & Come-Alongs

4.2.0 Plate Fit-Up Tools The most common method of holding a joint in place after it had been fitted up is to tack-weld it in place. The most common tools for plate fit-up are strong-backs, clips, yokes, and wedges.

4.2.1 Strongbacks Strongbacks are typically made on the job site from heavy bar stock. They are notched at the weld joint to allow access to the joint so that welds can be made without interference. The strongback can be on the face or root side of the weldment. When tack-welding strongbacks, place the tack welds on only one side of the strongback, so it will be easier to remove.

4.2.2 Clips, Yokes, and Wedges Clips, yokes, and wedges can be used to align joints and then hold them in place during the welding. Clips are welded to the edge of one plate and then wedges are positioned on the other plate and driven under the clips to force the joint alignment. Yokes work in a similar manner.

4.2.4 Plate Alignment Tools A typical configuration of an alignment tool consists of a yoke, threaded adjusting rod, gap plate, and root bar. The alignment tool is used by straddling the joint opening with the yoke. The gap plate can be changed to match the specified root opening.

15 minute break

4.3.0 Pipe Fit-Up Tools Pipe jacks and rollers are used to support pipe for fit-up and welding. Pipe jacks typically have either a V-head or roller head and a height adjustment. Rollers, which can be floor stand or table models, can be adjusted horizontally for various pipe diameters.

4.3.1 Pipe Jacks and Rollers Pipe jacks and rollers are used to support pipe for fit-up and welding. Pipe jacks typically have either a V-head or roller head and a height adjustment. Rollers can be adjusted horizontally for various pipe diameter.

4.3.1 Pipe Jacks and Rollers

4.3.2 Chain Clamps Chain clamps are used to align and hold pipe for fit-up and tacking. The chain, which is anchored to one side of the clamp, is passed around the pipe and secured. The slack in the chain is then removed using a screw jack to pull the pipe tightly against the clamp.

4.3.3 Other Pipe Alignment and Clamping Tools Cage clamps are another style of clamp that can also be used to for the same purpose. Cage clamps come in a variety of styles and sizes. All cage clamps must be installed manually. Cage clamps are good for aligning and holding two sections of straight pipe. They are of no use when a flange must be welded.

Cage Clamp

4.3.3 Other Pipe Alignment and Clamping Tools One of the devices used when welding flanges onto pipes is a rim clamp. The jack screws on a rim clamp exert pressure on specific high points so the precise alignment can be made. These clamps are ideal for tasks in which 100 percent weld and grind is required before the clamp can released.

Rim Clamp

5.1.0 Causes of Distortion Distortion is the expansion and contraction of metal as it responds to changes in temperature. Distortion is caused by the nonuniform expansion and contraction of the weld metal and adjacent base metal during the heating and cooling cycles of welding.

5.1.0 Causes of Distortion When the base metal is heated during the welding process, it will attempt to expand but will be restricted by the surrounding cooler base metal. Even when the weld is at room temperature, stress equal to the strength of the base metal will be locked in the weldment. This is called residual stress. 5.2.0 - The degree of distortion is directly related to the stresses generated during welding.

5.3.1 Clamping & Bracing Field fabricated alignment devices are often used to hold weldments firmly in place during the welding process. They must also be left in place long enough to allow the weldment to cool to ambient temperature.

5.3.2 Tack Welding A tack weld holds parts of a weldment in proper alignment until the finish welds are made. If too few tacks are made, the joint will close up as the weld proceeds.

5.3.3 Amount of Weld Material The more weld metal placed in a joint, the greater the forces of shrinkage. Excess reinforcement on the face of a weld increases the forces of the weld . Excess face reinforcement actually reduces the strength of a weld and is therefore prohibited by welding codes. Groove welds should have a slight reinforcement of no more than 1/8” for butt or corner welds.

5.3.3 Amount of Weld Material Proper fit-up and edge preparation also reduce the amount of weld required. Open-root joints should have a root opening from 1/16” to 1/8”. To control melt-through, a root face of 1/16” to 1/8” is used. Each side of the open-root joint is beveled from 30 to 37 ½ degrees. The bevel angle must be sufficient to allow access to the root.

5.3.4 Backing Strips on Groove Welds Various forms of the backing materials or strips can be applied to the back side of plate weldments. Temporary strips typically have a groove machined directly into them that controls the shape and size of the penetration material once it cools.

5.3.4 Backing Strips on Groove Welds If the backing strip is designed to become part of the permanent weldment, it must be made of material similar to the alloy or metal being welded. When thick metal backing strips are used on groove welds, the root opening normally opens to ¼” and the bevel is reduces to 22 ½ degrees.

5.3.5 Open Root Pipe Welds Molten metal that extends beyond the back or opposite side of the groove is called root reinforcement. When welding pipe, the amount of root reinforcement on the inside of the pipe must be controlled. Excessive root reinforcement on the interior of the pipe interferes with the flow in the pipe, causing turbulence and other problems.

5.3.6 Backing Rings Backing rings are flat metal strips that have been rolled to fit inside a pipe. They can be ordered in a variety of base metal types to match the base metal being welded. Backing rings have three or more nubs around the outside of the ring. The diameter of the nub is the root opening required for the pipe being welded. The nubs are removed by striking them with a chipping hammer.

5.3.6 Backing Rings

5.3.7 Consumable Inserts on Pipe Welds Consumable inserts are similar to backing rings. They are completely consumed during welding and become part of the finished weld. They must match the filler metal requirements for the weld being made.

5.3.8 Inserts on Socket Joints Socket joints generally are used on pipe that is 5” or smaller in diameter. A socket joint uses a prefabricated fitting containing sockets on the ends; the pipe slips into these sockets. The fitting and pipe are joined using a fillet weld.

5.3.8 Inserts on Socket Joints In order to eliminate stress, distortion, and possible cracking by expansion during heating, the end of the pipe must not touch the bottom of the socket. Socket welds require a 1/16” to 1/8” gap between the end of the pipe and the bottom of the socket fitting.

5.3.8 Inserts on Socket Joints There are two ways to ensure that the gap between the end of the pipe and the socket fitting is maintained. One way is to scribe the pipe a preset distance from the end. The gap is checked by measuring from the scribed line to the socket and then adding the socket depth.

5.3.8 Inserts on Socket Joints The second method of ensuring the correct gap is to use a gap ring. The gap ring is placed in the bottom of the socket and becomes a permanent part of the joint. Gap rings are commonly called gap-o-lets.

5.3.8 Inserts on Socket Joints

5.3.10 Backstep Welding Backstep welding is a welding technique in which the general progression of welding is from left to right. But the weld beads are deposited in short increments from right to left. This technique reduces distortion by minimizing and interrupting heat input.

5.3.10 Backstep Welding

5.3.11 Welding Sequence A welding sequence involves placing welds at different points on a weldment so that shrinkage forces in one location are counteracted by shrinkage forces in another location. A simple welding sequence is to make short welds on alternating sides of the joint. Welding sequences are often performed by two individuals welding on opposite sides of a joint at he same time. This type of welding is often called buddy welding. It is a very effective way to control distortion.

5.3.12 Heat Treatments Distortion can be controlled by preheating and postheating. Applying heat before welding is called preheating. Applying heat immediately after the welding is called postheating.

6.0.0 Checking Joint Misalignment and Fit-Up The quality of joint preparation and fit-up directly affects the quality of the completed weld. By thoroughly checking the joint fit-up, potential problems can be avoided. Check that the joint surfaces are free of contamination such as grease, oil, moisture and rust. If there is contamination, clean the joint before continuing.

Summary It is very important to perform proper joint fit up and alignment to ensure an acceptable weld. The proper fit-up measuring devices and tools must be used to accomplish this. Government agencies, professional societies, and associations have written guidelines for joint fit-up and alignment. All fit-up procedures should follow these guidelines.

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