Steel pipe weld grade classification and non-destructive testing requirements

Steel pipe weld quality standards
First, guarantee items.
1. Welding materials should comply with design requirements and relevant standards, and quality certificates and records should be checked.
2. Welders must pass the examination and check the welder’s corresponding welding conditions and the qualification certificate and assessment date.
3. Grade I and II steel pipe welds must be inspected by flaw detection and should comply with design requirements and construction and acceptance specifications. Check the flaw detection report of steel pipe welds.
4. Steel pipe weld surface Grade I and II steel pipe welds shall not have defects such as cracks, weld bumps, burn-throughs, and arc pits. Grade II steel pipe welds shall not have surface pores, slag inclusions, arc pits, cracks, arc scratches, etc., and Grade I steel pipe welds shall not have defects such as undercuts and incomplete welding.

Second, basic items
1. Appearance of steel pipe welds: The appearance of steel pipe welds is uniform, the transition between welds and welds, and between welds and base metals is smooth, and welding slag and spatter are cleaned.
2. Surface pores: Grade I and II steel pipe welds are not allowed; Grade III steel pipe welds are allowed to have a diameter of ≤0.4t per 50mm length of steel pipe welds; and ≤2 pores of 3mm; the spacing between pores is ≤6 times the aperture.
3. Undercut: Grade I steel pipe welds are not allowed. Grade II steel pipe welds: undercut depth ≤0.05t, and ≤0.5mm, continuous length ≤100mm, and the total length of undercuts on both sides ≤10% of the length of the steel pipe weld. Grade III steel pipe welds: undercut depth ≤0.lt, and ≤lmm. Note: t is the thickness of the thinner plate at the connection.

Third, finished product protection
1. Do not hit the joint after welding, and do not pour water on the newly welded steel. Slow cooling measures should be taken at low temperatures.
2. Do not arbitrarily strike an arc on the steel pipe outside the steel pipe weld.
3. Welding can only be carried out after various components are calibrated, and the pads and fixtures must not be moved at will to prevent component size deviation. The steel pipe welds in the hidden parts must go through the hidden acceptance procedures before the next hidden process can be carried out.
4. Low-temperature welding is not allowed to remove slag immediately and should be carried out after the steel pipe weld cools down.

Fourth, quality issues that should be paid attention to
1. Dimensions exceed the allowable deviation: For the length, width, thickness of the steel pipe weld, the center line offset, bending and other deviations, the relative position size of the welding part should be strictly controlled, and welding is allowed after passing the test, and the welding should be carefully operated.
2. Cracks in the steel pipe weld: To prevent cracks, appropriate welding process parameters and welding procedures should be selected, avoid using high current, do not suddenly turn off the flame, the steel pipe weld joint should overlap 10-15mm, and the wood is allowed to move and knock the weldment during welding.
3. Surface porosity: The welding rod is baked at the specified temperature and time, the welding area must be cleaned, and the appropriate welding current is selected during welding to reduce the welding speed so that the gas in the molten pool can escape completely.
4. Slag inclusion in the weld of steel pipe: The welding slag should be cleaned layer by layer during multi-layer welding. The operation should be carried out correctly and the arc length should be appropriate. Pay attention to the flow direction of the slag. When using alkaline welding rods, the slag must be left behind the slag.

Steel pipe weld grade classification and non-destructive testing requirements

Steel pipe welds should be selected according to the importance of the structure, load characteristics, steel pipe weld form, working environment, and stress state, and different quality grades should be selected according to the following principles:
1. In components that require fatigue calculation, all butt steel pipe welds should be welded through, and their quality grades are:
1) Transverse butt steel pipe welds or T-shaped butt and corner joint combined steel pipe welds with forces perpendicular to the length direction of the steel pipe weld should be graded as grade 1 when under tension and grade 2 when under compression;
2) Longitudinal butt steel pipe welds with forces parallel to the length direction of the steel pipe weld should be graded as grade 2.
2. In components that do not require fatigue calculation, all butt steel pipe welds that are required to be as strong as the steel pipe should be welded through, and their quality grade should not be lower than grade 2 when under tension and should be grade 2 when under compression.
3. The T-joint steel pipe welds between the web and L flange of the crane beam with heavy duty and lifting capacity Q≥50t and between the upper chord and node plate of the crane frame are required to be fully welded. The steel pipe welds are generally a combination of butt and fillet welds, and their quality grade should not be lower than Grade 2.
4. The angle steel pipe welds used in the ‘I’-shaped joints that do not require full penetration or the partially fully welded butt and fillet welds, as well as the angle steel pipe welds used in the lap joints, have the following quality grades:
1) For structures that directly bear dynamic loads and need to verify fatigue and crane beams with medium-duty and lifting capacity equal to or greater than 50t, the appearance quality standard of the steel pipe welds shall meet Grade 2;
2) For other structures, the appearance quality standard of the steel pipe welds maybe Grade 2.
Appearance inspection is generally done by visual inspection. Crack inspection should be assisted by a 5x magnifying glass and carried out under appropriate lighting conditions. Magnetic particle inspection or penetrant inspection can be used when necessary. Dimensional measurement should be done with measuring tools and calipers.