Galvanized pipes and black steel pipes are both commonly used pipe materials in engineering, but they are very different in corrosion resistance, pressure bearing capacity, installation cost and other aspects. In order to better help you choose the most suitable pipe, this article will analyze the differences between the two in detail.
Galvanized vs Black Steel Pipe Comparison
Comparison Dimensions | ||
Anti-corrosion mechanism | Sacrificial anode protection (zinc layer preferentially oxidized) | Reliance on iron oxide passivation layer |
Salt spray life | 2000 hours without red rust | Red rust appears after 72 hours |
Coating Thickness | 80-120μm (hot dip galvanized) | No coating, oxide layer ≤ 5μm |
Initial Cost | ¥42.8/m (including galvanizing process) | ¥28.5/m (basic material) |
Service life | 25 years+ (ISO 9227 certified) | 5-8 years (humid environment) |
Pressure bearing capacity | 28MPa (Zinc layer reduces strength) | 32MPa (thick wall pipe) |
Welding Limitations | Welding is prohibited (damage to zinc layer) | Support arc welding/TIG welding |
Applicable environment | pH 3-11, chloride ion＞500ppm | Dry environment with humidity less than 60% |
Maintenance Requirements | No active maintenance required (self-healing) | Apply anti-rust paint every 2 years |
Weight Difference | Increase 4-7% (zinc coating weight) | Base weight (no additional layers) |
Black Steel Pipe Specification
First choice for dry environments
Black steel pipe is a kind of steel pipe widely used in various scenarios. It is manufactured by hot-rolled steel coil welding process. Although it is not treated with anti-corrosion, a layer of naturally formed Fe₃O₄ is left on the surface, so it also has a little corrosion resistance. According to the ASTM A53 standard, the typical characteristics of this pipe include:
Wall thickness range: usually between 2.5 and 10 mm, which is more suitable for high-pressure scenarios.
Working temperature: The working temperature range of black pipe is very wide. It can usually operate stably in an environment of -29℃ to 427℃, so it is often used for gas transportation or high-temperature medium environment transportation.
Advantage scenario: Black pipe complies with the national standard GB 50028 and is widely used in the transportation of natural gas and liquefied gas. In the fire dry sprinkler system, the black pipe does not come into direct contact with water, which effectively avoids water corrosion, so it is also used in the fire dry sprinkler system. The cost of black pipe is lower and it can be flexibly disassembled, so it is often used as a temporary support material.
Galvanized Pipe Specification
Effective anti-corrosion properties
Galvanized pipe is a widely used building material. This kind of steel pipe uses hot-dip galvanizing process to form a zinc layer (Zn+Fe alloy layer) with a thickness of usually 80-120μm on the surface of the pipe. It has very good anti-corrosion performance and effectively isolates it from the external environment.
Laboratory data shows:
Salt spray test life:
Black steel pipe: Red rust appears after 72 hours, indicating that the anti-corrosion performance is very general.
Galvanized pipe: Only slight zinc oxidation appears on the surface after 2000 hours, and the anti-corrosion performance is excellent.
Installation precautions:
Thread cutting is prohibited. Cold galvanizing paint must be applied to avoid bare steel exposure and corrosion.
Welding is prohibited because high temperature will destroy the galvanized layer, resulting in exposed bare steel causing corrosion. Therefore, mechanical connection and other connection methods that do not damage the galvanized layer should be used.
Galvanized and Black Pipe Appliance
Black steel pipes appliance
Short-term projects (<3 years) with limited budgets: The price of black pipes is relatively low, and the strength is acceptable, with a high cost-effectiveness. For temporary construction or short-term projects, black pipes can be selected to reduce costs.
Dry gas transportation (oxygen/nitrogen pipeline system): Black pipes are more advantageous in transporting dry gas, because there is no liquid, so the corrosion is low. Choosing black pipes is economical and can meet the transportation needs.
Temporary structures that require on-site welding and modification: Black pipes are very suitable for on-site welding, so black pipes can be selected for construction sites that need to be quickly built or temporarily modified, and can be flexibly adjusted according to actual conditions.
Galvanized pipes appliance
Seawater aquaculture water supply network: There is a high concentration of chloride ions in seawater. It will cause extremely strong corrosion. In this case, only galvanized steel pipes with the highest corrosion resistance can be used.
Acid-base medium transportation in chemical plants: For media with a pH value of 3 to 11, ordinary steel pipes are easily corroded, so galvanized steel pipes with the highest corrosion resistance must be used.
Pipelines buried 3 meters underground: Humidity and chemical components in the soil will corrode the pipelines. Galvanized pipes will resist corrosion in the soil and extend their service life.
FAQs：
1. Can galvanized pipes and black steel pipes be used together?
No! It will cause electrochemical corrosion and accelerate the consumption of the zinc layer.
2.How to determine whether the pipe should be replaced?
Black steel pipe: Surface rust area > 15%
Galvanized pipe: Continuous white rust (ZnO) and bulging
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