I. Welding Connection Specifications
1. Welding Process Requirements
Before welding, check the equipment to ensure that parameters such as current, voltage, and welding speed meet standards.
Welding methods include manual arc welding and gas shielded welding. The appropriate process should be selected based on the pipe material, diameter, and wall thickness.
After welding, remove weld slag and spatter, and perform a visual quality inspection and non-destructive testing (such as radiographic or ultrasonic testing).
2. Weld Position and Quality
Longitudinal welds should be located approximately 45° from the upper semicircle perpendicular to the center of the pipe and staggered (≥100mm for pipe diameters <600mm, ≥300mm for pipe diameters ≥600mm).
Circumferential welds must maintain a net distance of ≥100mm from the support. The spacing between adjacent circumferential welds must be ≥200mm and no less than the outer diameter of the pipe segment.
Cross welds are prohibited, and the stagger deviation must be ≤20% of the wall thickness and ≤2mm. 3. Bevel and Assembly Requirements
The bevel angle, blunt edge, and gap must meet design requirements. Welding of side bars or heating to reduce gaps is prohibited.
Before assembly, clean the inside and outside of the bevel to remove any oil, rust, or other contaminants. The thickness difference between pipe sections of different wall thicknesses should be ≤3mm.
II. Flange Connection Specifications
1. Flange Installation Requirements
The flange and pipe must be concentric, with parallel flange surfaces. Bolts must be of the same specification and installed in the same direction.
Bolts must be tightened symmetrically, with 2-3 threads exposed. Flange joints must be treated with corrosion protection when buried underground.
2. Sealing and Anti-corrosion
Flexible joints allow axial staggering of 3-5mm; rigid joints prohibit axial staggering.
After flange connection, clean any exposed threads and scratches, and apply corrosion protection.
III. Other Connection Methods
1. Compression Connection
The connection is completed by tightening the nut against the sleeve and compressing the sealing ring. Ensure a tight seal. 2. Press-Fit Connection
A special tool presses the pipe wall into a hexagonal shape, deforming the sealing ring to achieve a seal.
3. Threaded Connection
Applicable to pipes with a DN < 80. After threading, burrs must be trimmed and debris removed. The exposed threads should be 2-3 turns.
IV. Special Environmental Requirements
Winter Welding: Preheating is required according to the ambient temperature. For example, carbon steel with a carbon content ≤ 0.2% should be preheated at ≤ -20°C for a width ≥ 40mm.
Non-destructive Testing: Pressure pipelines must undergo radiographic and ultrasonic testing according to design or specification requirements, with a sampling rate of ≥ 10%.
V. Quality Inspection
Main Control Items: The quality of pipe joints and welding materials, the pass rate of weld non-destructive testing, and groove dimensions must be inspected for each joint.
General Items: Weld appearance (absence of weld burrs, undercuts, etc.) and anti-corrosion treatment (such as masking tape) must comply with GB50236.
