Weld Defects

Defects in welds and joints made by fusion welding, arise from violations of regulatory requirements for the preparation, assembly and welding of connected components, mechanical and thermal treatment of welded joints and the structure itself, the welding material.

The defects of welded joints can be classified according to various criteria: shape, size, location in the weld, the reasons of education, the degree of danger, etc. The best known is the classification of defects, the recommended standard for interstate GOST 30242-97, "Defects in connection with fusion welding of metals. Classification, identification and determination " . Under this standard, the defects of welded joints are divided into six groups:

• cracks;
• cavities, pores, fistulas, cavities, craters;
• solids;
• incomplete and lack of penetration;
• violation of weld shape - undercuts, grooves shrinkage, excess convexity, excess proplava, afloat, displacement, sinters, burn marks, etc.;
• other defects.

Each type of defect corresponds to the numerical designation, and possibly lettering, as recommended by International Institute of Welding (IIW).

According to GOST 30242-97 crack is lack of adhesion caused by local rupture of the seam or weld zone, which may arise as a result of cooling loads or actions.

Depending on the orientation of the crack can be divided into

• longitudinal (oriented parallel to the axis of the weld) - numbered 101, the letter of Ea;
• transverse (oriented perpendicular to the axis of the weld) - 102, Eb;
• radial (radiating from one point) - 103, E.

They can be located in the weld metal, heat-affected zone, the base metal.

Also identify the following types of cracks:

• placed in the crater of the weld - 104, Ec;
• separate group - 105, E;
• branched group - 106, E;
• microcracks (1001), detected by physical methods is not less than 50 tikratnom increase.

The gas cavity (GOST 30242-97) - is a cavity of arbitrary shape with no corners, formed by gases, the detainees in the molten metal. Sometimes (sometimes gas, 2011) is a gas cavity is usually spherical in shape. Letter designation of the gas pores, used ISI, - Aa. Pores can be divided into

• uniformly distributed over the weld seam - 2012;
• located cluster - 2013;
• located Chain - 2014.

For elongated cavities (2015, Ab) are discontinuities, elongated along the axis of the weld. Fistula (2016, Ab) - elongated tubular cavity caused by the release of gas.

To also include cavities cavities (202, R) and craters (2024, K). Piping (GOST 30242-97) - a cavity which is formed as a result of shrinkage during solidification. crater called nezavarennaya piping at the end of the weld bead.

Solids (300) - is a solid metallic foreign substances or non-metallic origin, remaining in the weld metal. Acute-angled inclusions are called inclusions with at least one acute angle. Types of solids:

• slag inclusions (301, Ba) - linear (3011), separated (3012), others (3013);
• flux of (302, G) - linear (3021), separated (3022), others (3023);
• oxide inclusions (303, J);
• metallic inclusions (304, H) - Tungsten (3041), copper (3042), other metal (3043).

Poor fusion (401) is the lack of connection between the metal and the weld or base metal between the individual rollers of the weld. Types of poor fusion:

• on the lateral surface (4011);
• between the rollers (4012);
• at the root of the weld (4013).

Lack of penetration (402, D) or incomplete penetration - a poor fusion of the base metal at the site or the entire length of the seam that appears due to the inability of the molten metal to penetrate into the root of the compound (to fill the gap between the parts).
Violation of the weld shape (500) - is the deviation of the external surfaces of the weld geometry or connections from the specified value. For violations of the forms in accordance with GOST 30242-97 weld include:

• undercuts (5011 and 5012; F);
• shrinkage grooves (5013);
• convexity of the excess butt (502) and angular (503) joints;
• excess proplava (504);
• irregular profile of the seam (505);
• naplav (506);
• linear (507) and angular (508) displacement of welded elements;
• incrustation (509);
• burn-through (510);
• not completely filled with cutting edges (511);
• extreme asymmetry of the fillet weld (512);
• non-uniform width of joint (513);
• rough surface (514);
• concavity of the root of the weld (515)
• and others

Undercut - a longitudinal grooves on the outer surface of the roller seam. Undercuts the root of the weld due to the shrinkage of one-way along the border are called shrinkage grooves . proplava excess - the excess weld metal at the back of the butt weld. concavity of the root pass - a shallow groove from the root of the weld, which arose due to shrinkage.

The offset between welded components with their parallel arrangement at different levels is called the linear displacement , and at the location of the edges of elements at an angle - angular displacement . Excessive asymmetry of the fillet weld size is a significant excess of one leg over the other.

Naplav - is an excess of the deposited weld metal, natekshy on the surface of the base metal. Nateq - a weld metal with no fusion of the joined surface and formed as a result of redistribution of the deposited weld metal by the force of gravity. Incrustations often occur during welding of fillet welds and butt welds in the horizontal position.

Burn-through - streaming metal weld pool, leading to the formation of through-hole in the seam. If the wrong profile joint angle between the surface of the base metal and the plane tangent to the surface of the weld is less than normal value.

All defects that are not included in groups 1-5 (GOST 30242-97), relate to other defects (600):

• local damage to the metal due to accidental ignition of the arc (601);
• spatter (602);
• scratches the surface (603) - surface damage due to the removal temporary welded aids;
• thinning of the metal (606)
• and others

This classification is useful for a static account of defects and to assess their risk, interpretation of NDT results, as well as in several other cases. At the same time it does not adequately reflect the mechanism of formation of defects in metals. Therefore, the analysis of metallurgical and process causes of defects using a different classification. For example, cracks are divided into hot and cold. Hot cracks are divided into crystallization, precipitation hardening, podsolidusnye and cold cracks - in the martensite, intermetallic, lamellar, etc.

See also:
welds and joints