How to determine the galvanizing process of a galvanized pipe?
1. Most intuitive: Observe the surface condition (initially distinguish at a glance)
The surface differences between hot-dip galvanizing and cold-dip galvanizing are very obvious, making this the easiest method to use.
2. Most reliable: Scratch test (to determine the adhesion strength of the zinc layer)
The hot-dip galvanized zinc layer is "molten" and penetrates the substrate surface, resulting in extremely strong adhesion. Cold-dip galvanizing is a thin zinc layer "electrolytically deposited" with weaker adhesion, resulting in a noticeable difference after scratching.
Testing tools: Use a hard object (such as a key, screwdriver tip, or the back of a utility knife).
Testing method: Use moderate force to make one or two horizontal scratches approximately 5 cm long on an inconspicuous area of the pipe (such as the inside or end of the pipe wall). Observe the scratched area. Judgment Result:
Hot-dip galvanized pipes: Scratches will only produce "white marks" (exposing the base material), but the zinc layer will not flake off in pieces, and even scratching with a fingernail will be difficult. If small particles break off from the scratches, these are mostly surface zinc nodules and do not affect overall adhesion.
Cold-dip galvanized pipes: Scratches will easily cause "zinc peeling," and even tiny zinc flakes will fall off when scratched. In severe cases, the underlying black iron base material can be directly visible, and the peeled zinc layer will appear thin and film-like.
3. More Accurate: Measuring Zinc Layer Thickness (Requires simple tools, suitable for critical scenarios)
If precise judgment is required (such as during project acceptance and procurement selection), simple tools can be used to measure zinc layer thickness. This is a key indicator for distinguishing process technologies (hot-dip galvanizing produces a much thicker zinc layer than cold-dip galvanizing). Professional Tool Method: Use a "zinc coating thickness gauge" (handheld, portable models are inexpensive and suitable for frequent use) to directly measure:
Hot-dip galvanized pipes: The zinc coating thickness is typically ≥60μm, with engineering pipes reaching 80-120μm.
Cold-dip galvanized pipes: The zinc coating thickness is generally ≤30μm, with most being between 10-20μm, significantly thinner than hot-dip galvanized pipes.
Simple Comparison Method (for use without tools):
Observe the "cross-section" of the pipe end: A clear "zinc coating" (silver-gray layer) can be seen on a hot-dip galvanized pipe cross-section, and the thickness is visible to the naked eye. On a cold-dip galvanized pipe cross-section, the zinc coating is extremely thin, with an almost invisible silver-gray layer, leaving only the black base material visible.
Weighing Comparison (for pipes of the same specification): Due to the thicker zinc coating, hot-dip galvanized pipes weigh 5%-10% more than cold-dip galvanized pipes of the same diameter and wall thickness. (For example, a 1-meter-long DN50 pipe may weigh 0.3-0.5kg more for hot-dip galvanized pipes than for cold-dip galvanized pipes.)