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Shielded Metal Arc Pipe Welding Lecture
Transcript of Shielded Metal Arc Pipe Welding Lecture
API - American Petroleum Institute
ASME - American Society of Mechanical Engineers
AWS - American Welding Society
DOT - Department of Transportation
Hot Line - a line containing or transporting oil, gas, or any potentially flammable or explosive substance.
Nominal - reference to pipe that may vary slightly from stated measurements because of uncontrollable variations in the manufacturing process.
Transmission Line pipe welding - The welding of pipes used to carry liquids, gasses, and sometimes solids mixed with liquids.
Industrial pipe welding - The welding of pipes used in fixed installations that refine and store oil and gas, manufacture chemicals or control any materials in a flow-type production facility. Page 8 Characteristics of transmission-line pipe welding - (Low Pressure - API)
a. Most transmission-line pipe welding is welded vertical down to givefaster welding speed on pipe thicknesses of less than 1/2" with a 1/64" root gap.
b. Stovepipe arrangement... all joints are welded to the pipeline one section at a time.
c. Most transmission-line pipe welding used for cross-country work uses one crew to lay the stringer bead, another crew to make the hot pass and a thrid crew to lay the filler and cap. Page 9 API classification for transmission-line pipe
a. All transmission-line pipe has a designation of 5L with the "5" indicating the general category and the "L" indicating line pipe.
b. High test line pipe is designated as 5LX with the "X" indicating extra stength.
c. Numbes following the "X" are the first two digits fo the minium yield strength of the pipe expressed in thousands of pounds per square inch. Page 8 How a cross-country pipe welding crew operates
a. Two welders working together align the pipe, tack weld, and make the first pass or stringer bead.
Note: When internal line-up clamps or "grasshoppers" are used tack welds are not required, but when external clamps are used, tack welds are required.
b. A hot pass crew then moves in to make the second pass or hot pass after the stringer has been cleaned with a power wire brush or grinder.
c. After the hot pass is cleaned, the filler and cover-pass crew finishes the weld and cleans it for inspection. Page 9 Characteristics of industrial pipe welding (High Pressure Pipe - ASME)
a. Most industrial pipe welding is welded vertial up with a 3/32" root gap that requires smaller electrodes than transmission-line welding with slower welding speeds.
b. Most industrial pipe welding is done under stricter codes than required for transmission-line welding because the higher pressures pose a greater danger to people and property.
c. Industrial pipe welding uses a greater variety of alloy steels than transmission-line piping.
d. Industrial pipe welding sometimes requires a welder to work in confined areas so cramped that a mirror has to be used to get a good view of the work and a bent electrode has to used to reach the work.
e. Industrial pipe welding is often done in a shop where the pipe can be rolled to avoid out-of-position welding.
f. Industrial pipe welding joints are usually completed stringer to cap by one welder, not a team of welder as in cross-country work.
Examples: Ethanol Plants, Chemical / Petro Chemical , Fossil Fuel / Nuclear Power Plants and Steam Piping Systems Socket Welding Side Booms HF - Hot Fill
HP - Hot Pass
B - Bead Pass Cross Fitting Tee Fitting Nipples Reducers Elbows Y Connections Threadolets Weldolets End Caps Shielded Metal Arc Pipe Welding Page 16 AWS guidelines for G-position qualification
a. Qualification in the 1G position qualifies for welding only in the 1G position.
b. Qualification in the 2G position qualifies for welding in the 1G and 2G position.
c. Qualification in the 5G position qualifies for welding in the 1G and 5G position.
d. Qualification in both the 2G and 5G positions qualifies for welding in any position because it includes elements of all positions.
e. Qualification in the 6G and 6GR positions qualifies for welding in any postion because they include elements of all welding positions.
f. Groove weld qualification shall also qualify plug & slot welds for the test position indicated. Page 18 NEVER cut into or weld on a line without knowing for certian that it is safe.
NEVER cut into or weld on a hot line without going through the proper procedure for obtaining a "hot work" or entry permit from a supervisor authorized to grant such permission.
Types of line-up clamps
a. Internal line-up clamps fit inside to align connecting sections of pipe or pipe-to-flange fit-ups, and are sometimes specified for use with large dimeter piping.
b. External line-up clamps fit outside pipes to align connecting sections of pipe or pipe-to-flange fit-up so pipes can be tacked in place prior to welding. Page 17 AWS guidelines for F-position qualification
a. Qualification in the 1F position qualifies for fillet welding only in the 1F position.
b. Qualification in the 2F position qualifies for fillet welding in the 1F and 2F positions only.
c. Qualification in the 4F position qualifies for fillet welding in the 1F, 2F, and 4F positions only.
d. Qualification in the 5F position qualifies for fillet welding in any welding position because it includes elements of all welding positions.
e. Qualification in any of the fixed G positions qualifies for the fillet welding of any fillet welds in pipe. Page 19 Pipe Beveling Machines
a. Most beveling machines cut bevel angles as required in almost all positions and on pipe diamters ranging from 2" to 74"
b. Pipe beveling machines are often oxyfuel rigs but may be electric or pneumatic.
c. Portable pipe beveling machines are popular due to portability.
d. Stationary pipe beveling machines are popular in fabrication shops and vocational training programs because they are easy to operate and reduce wasted pipe. Page 20 Jack (pipe) stands and their uses
a. Jack stands are used primarily to align pipe to be welded and to support it while it is being welded or tacked.
b. Jack stands cradle pipe in a v-shaped channel that can be vertically adjusted to raise or lower a pipe section soit can be aligned with an adjoining section.
c. Jack stands used in pairs or several jack stands used on long lengths of adjoining pipe have to be manually positioned for side to side alignment.
d. Some jack stands come equipped with hold-down chains or devices that fit over the pipe to secure it to the stand for situations that require fit-ups with close tolerances. Page 20 - 21 Center finders and their uses
a. Used to find the center of a pipe by using an adjustable protracot and a dial bubble.
b. Center finders may have centering pins that are spring loaded and manually activated or centering pins that have to be struck with a hammer to mark the center of the pipe.
c. Center finders can also be used for establishing and marking angles for of center fit-ups and for both pipe and tank layout.
a. Standard contour markers are used for finding and marking contours and angles on pipe diameters from 1 1/2" - 18". Page 22 Wrap-arounds and thier uses
a. Wrap-arounds are usually made of durable gasket materials with edges that are perfectly straight and parallel.
b. Wrap-arounds are used primarily for making a straight line around the end of a pipe so that the end may be squared. (90 degrees)
c. The wrap-around should be long enough that it can wrap around the pipe aat least two times. Page 23 Page 23 Templates and their uses
a. Templates are pre-cut patterns made for specific diameters of pipe as guides for cutting tees, elbows, and almost all types of pipe fittings.
b. Manufactured templates are available in sets for specific diameters of pipes, but many templates are laid out and cut in a shop or at a job site to eliminate the need for repeated figuring of pipe joints that are used often in one application.
Two-hole pins (2 - holes) have a level-type bubble which is used to level the top or bottom two holes of a flange by inserting the two pins in adjacent bolt holes and moving the flange until it is level. Thisassures that the connecting flanges will be in line and on center.
Backing-up rings (backing rings) are used inside connecting but joints to help alingn them provide proper root gap, and control penetration in the weld zone.
API classification for transmission-line pipe Page 12 a. A pipe welder has to weld in whatever position it requires to reach the joint.
b. A pipe welder has to maintain a constant electrode angle as the bead is moved around the circumference of the pipe.
c. Pipe welding demands more manual dexterity than plate welding because there must be a greater amount of hand travel compared to the travel at the end of the arc.