I. Air bubbles or pores in the weld
This is one of the most common internal defects during welding, manifesting as voids or honeycomb structures inside the weld, severely affecting joint strength.
Main causes: Moisture, oil, or dust contamination of the pipe or joint area can cause moisture or impurities to decompose and produce gas during high-temperature melting; water content in the raw material itself or insufficient drying can also lead to pore formation.
Prevention recommendations: Ensure the pipe ends are dry and clean before welding. Wipe with a special cleaning agent and remove the surface oxide layer with a scraper. Avoid working in rainy or humid environments.
II. Incomplete weld (lack of fusion or poor fusion)
This refers to the two pipe ends failing to truly fuse, only superficially adhering. The joint strength is extremely low, and it is very prone to cracking during pressure testing.
Typical manifestations: Loose, easily peeled edges; obvious delamination or exposed fusion line visible after cutting.
Cause analysis: Insufficient heating temperature, too short heat absorption time, too long switching time leading to cooling of the molten surface, or insufficient butt joint pressure.
Key Control Points: Strictly adhere to the heating temperature settings for PE80 (210±10℃) and PE100 (225±10℃). Refer to the empirical formula "pipe diameter ÷ SDR × 10" seconds for heat absorption time, and control the switching time to within 10 seconds.
III. Misalignment and Poor Alignment: Misalignment of the two pipe axes after welding causes uneven stress on the joint, leading to fatigue cracking during long-term operation.
Allowable Range: Misalignment must not exceed 10% of the pipe wall thickness (e.g., ≤0.6mm for a 6mm wall thickness).
Main Causes: Uncalibrated clamps, insecure pipe fixing, incomplete milling, or uneven ground causing misalignment.
Solutions: Carefully adjust the clamp level before welding to ensure the pipe ends are flat and aligned. Perform secondary milling correction if necessary.
IV. Abnormal Edge Rolling: Edge rolling is an important visual indicator of welding quality, directly reflecting the process execution.
Insufficiently rolled edge: Usually caused by insufficient heating or pressure, resulting in incomplete melting.
Excessively rolled edge: Often caused by excessive pressure or prolonged heating time, potentially masking internal defects.
Asymmetrical rolled edge: Indicates centering deviation or heating plate tilt, affecting joint uniformity.
Rolled edge breakage or cracking: May be caused by rapid cooling, material degradation, or internal stress.
✅ It is recommended to visually inspect each weld joint and rework immediately if any abnormalities are found.
V. Cold Welding Defects This is a highly concealed and harmful defect. It appears normal on the outside, but the internal fusion is incomplete.
Characteristics: The weld surface is smooth, but it breaks prematurely during tensile or compressive testing.
Main Causes: Low welding temperature, insufficient fusion time, or excessively low ambient temperature without compensatory measures.
Special Reminder: Cold-welded joints may not leak during initial pressure testing, but they are highly susceptible to failure after prolonged pressure. It is recommended to conduct random inspections using non-destructive testing methods such as Phased-Array Ultrasonic Testing (PAUT) for critical projects.
VI. Other Common Problems
Flanging, warping, or overflow: Often caused by an unclean heating plate or impact to the pipe end during removal.
Necking: Caused by excessive welding pressure, especially in small-diameter pipes (dn≤90mm), resulting in a reduced water flow area.
Incomplete fusion of electrofusion connection: Caused by excessive gap between the pipe and the electrofusion sleeve, incomplete cleaning of the surface oxide layer, or unstable voltage.
