Weld from the bottom up.
Like building a house, you cannot start the bricks at the top. Weld metal is a liquid. When it goes in it needs support, that is why we need to always start at the bottom.
It should be remembered that welding over weld metal is actually a very common occurrence. Multi-pass welds after all are manufactured by welding over weld metal! There are also many accepted procedures in which welds overlap.
Signs of a bad weld include: Lack of uniformity, cracks down the middle of the bead, too thin, and/or a lack of discoloration of the parent metal (which should be about 1/8 of an inch).
Weld Crack. The most serious type of welding defect is a weld crack and it's not accepted almost by all standards in the industry. It can appear on the surface, in the weld metal or the area affected by the intense heat.
Bubble Gum: A poor quality weld that looks like chewed bubble gum. Busted Out: Failed a weld test.
TIG welding is the hardest form of welding to learn for a variety of reasons. The process of TIG welding is slow and takes time to get used to as a beginner. A TIG welder requires a foot pedal to feed the electrode and control the variable amperage while maintaining a steady hand at the welding torch.
Three of the most common are Arc, MIG (Metal, Inert Gas) or GMAW (Gas, Metal Arc Welding), and TIG (Tungsten Inert Gas) welding. In order to know which process is best for the particular job you're working on, here's what you should know about each of them. Arc welding is the oldest of these three welding processes.
The major cause of a crack is when internal stresses exceed the strength of the weld metal, the base metal, or both. And once a focal point for these stresses—that is, a stress riser—develops and accumulates, a crack can propagate.
Where cracking occurs in or adjacent to welded joints, a satisfactory repair may be made by welding. It is important that the cracked material is gouged or machined away sufficiently to permit a full penetration repair weld to be made, with no traces of crack left behind and no new significant defects introduced.
A weld that is too small or too short for the application can fail from tension, compression, bending or torsional loads. If a weld is made to be in an application where a cyclical load is going to be applied, it will be beneficial to consider a filler metal option with increased impact toughness and ductility.
Chromium is a component in stainless steel, nonferrous alloys, chromate coatings and some welding consumables. . Chromium is converted to its hexavalent state, Cr(VI), during the welding process. . Cr(VI) fume is highly toxic and can damage the eyes, skin, nose, throat, and lungs and cause cancer. .
The most common used codes or regulations are API Standard 1104, American Petroleum Institute— Used for pipelines, ASME Section IX, American Society of Mechanical Engineers—Used for pressure vessels and nuclear components, and AWS D1. 1, American Welding Society—Used for bridges, buildings, and other structural steel.
Too cold and the bead is sitting on top of the work piece with little or no penetration. Too hot and it is probably burning through. As you move towards the middle, you may need to examine the weld bead closer. If the current is too low and wire speed too high, the resulting weld bead is taller with steeper edges.
Characteristics of a Good Weld
The sign of a quality and secure weld is that you will not see the weld at all. If there is any visible evidence of a weld, it will be in the form of a bead that has no holes or cracks and is uniform overall. A high-quality weld is made using high-quality materials.
Too much heat will likely cause cracking in the weld, oxide inclusion, softening of the heat-affected zone, and porosity—all of which degrade your material and affect the quality of your weld, both structurally and cosmetically.
Some examples of material combinations that cannot be fusion welded successfully are aluminum and steel (carbon or stainless steel), aluminum and copper, and titanium and steel. Nothing can be done to alter their metallurgical properties.
For the Cr-Mo steels, up to two re-welds may be carried out, but consideration needs to be given to the post-weld heat treatment operations and possible resultant degradation of the welded joint.