PRE-Galvanized Pipe
What is Pre-Galvanized Pipe?
A pre-galvanized pipe, also known as inline galvanized pipe or continuous galvanized pipe, is a type of pipe that is made of pre-galvanized coils and strips. This material has been pre-coated with a layer of zinc before rolling into a pipe. This coat helps to protect the pipe from corrosion and also provides a barrier against weld seam corrosion. The coating is applied before the pipe is welded, and the entire process is typically done in a factory setting. First, the steel strip is cleaned and then a coat of zinc is applied. The strip is then passed through a series of rollers to form it into a pipe shape. Next, the weld seam is created, and finally, the pipe undergoes a final spray coating of zinc. This coat helps to protect the weld seam from corrosion. Pre-galvanized pipes are often used in construction and manufacturing applications where they are exposed to corrosive materials.
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The Application of Pre-Galvanized Pipe
Pre-galvanized steel pipes are widely utilized in a variety of applications, including steel structures, building structures, guard rails, fences, metal furniture, solar structures, and so on.
Dimensions and Sizes of Pre-Galvanized Pipe
| DN | O. D. | W. T. | |||||||||||||||
| Inch | mm | SCH5S | SCH10S | SCH10 | SCH20 | SCH30 | SCH40 | SCH60 | SCH80 | SCH100 | SCH120 | SCH140 | SCH160 | STD | XS | XXS | |
| 50 | 2″ | 60.3 | 1.65 | 2.77 | – | – | – | 3.91 | – | 5.54 | – | – | – | 8.74 | 3.91 | 5.54 | 11.07 |
| 65 | 2 1/2″ | 73 | 2.11 | 3.05 | – | – | – | 5.16 | – | 7.01 | – | – | – | 9.53 | 5.16 | 7.01 | 14.02 |
| 80 | 3″ | 88.9 | 2.11 | 3.05 | – | – | – | 5.49 | – | 7.62 | – | – | – | 11.13 | 5.49 | 7.52 | 15.24 |
| 90 | 3 1/2″ | 101.6 | 2.11 | 3.05 | – | – | – | 5.74 | – | 8.08 | – | – | – | – | 5.74 | 8.08 | – |
| 100 | 4″ | 114.3 | 2.11 | 3.05 | – | – | – | 6.02 | – | 8.58 | – | 11.13 | – | 13.49 | 6.02 | 8.56 | 17.12 |
| 125 | 5″ | 141.3 | 2.77 | 3.4 | – | – | – | 6.55 | – | 9.53 | – | 12.7 | – | 15.88 | 6.55 | 9.53 | 18.05 |
| 150 | 6″ | 168.3 | 2.77 | 3.4 | – | – | – | 7.11 | – | 10.97 | – | 14.27 | – | 18.26 | 7.11 | 10.97 | 21.95 |
| 200 | 8″ | 219.1 | 2.77 | 3.76 | – | 6.35 | 7.04 | 8.18 | 10.31 | 12.7 | 15.09 | 18.26 | 20.62 | 23.01 | 8.18 | 12.7 | 22.23 |
| 250 | 10″ | 273.1 | 3.4 | 4.19 | – | 6.35 | 7.8 | 9.27 | 12.7 | 15.09 | 18.26 | 21.44 | 25.4 | 28.58 | 9.27 | 12.7 | 25.4 |
| 300 | 12″ | 323.9 | 3.96 | 4.57 | – | 6.35 | 8.38 | 10.31 | 14.27 | 17.48 | 21.44 | 25.4 | 28.58 | 33.32 | 9.53 | 12.7 | 25.4 |
| 350 | 14″ | 355.5 | 3.96 | 4.78 | 6.35 | 7.92 | 9.53 | 11.13 | 15.09 | 19.05 | 23.83 | 27.79 | 31.75 | 35.71 | 9.53 | 12.7 | – |
| 400 | 16″ | 406.4 | 4.19 | 4.78 | 6.35 | 7.92 | 9.53 | 12.7 | 16.66 | 21.44 | 26.19 | 30.96 | 36.53 | 40.49 | 9.53 | 12.7 | – |
| 450 | 18″ | 457.2 | 4.19 | 4.78 | 6.35 | 7.92 | 11.13 | 14.27 | 19.05 | 23.83 | 39.36 | 34.93 | 39.67 | 45.24 | – | – | – |
| 500 | 20″ | 508 | 4.78 | 5.54 | 6.35 | 9.53 | 12.7 | 15.09 | 20.62 | 26.19 | 32.54 | 38.1 | 44.45 | 50.01 | – | – | – |
| 550 | 22″ | 558.8 | 4.78 | 5.54 | 6.35 | 9.53 | 12.7 | – | 22.23 | 28.58 | 34.93 | 41.28 | 47.63 | 53.98 | – | – | – |
| 600 | 24″ | 609.6 | 5.54 | 6.35 | 6.35 | 9.53 | 14.27 | 17.48 | 24.61 | 30.96 | 38.89 | 46.02 | 52.37 | 59.54 | – | – | – |
The Process of Producing Pre-Galvanized Pipe
The manufacturing process of pre-galvanized pipe is very similar to that of normal welded pipe. The only differences are the raw material and zinc spray. The raw material of the pre-galvanized pipe is pre-galvanized strips, and the strips are galvanized already before pipe production. However, the welding seam will be the only part without zinc coating, so the zinc spray process shall be applied after the welding process.
What is Pre-Galvanizing？
When steel components are used in the manufacturing of a more sophisticated completed product, they may be galvanized before assembly. This is referred to as pre-galvanization, or “pre-gal.” It is also known as “in-line,” “continuous,” or “mill” galvanizing. Steel components, such as sheets or wire, are galvanized using an automated process before being reduced to size.
Inline, or continuous, galvanizing is an alternative method of applying zinc to steel handrail tubing. In this process, the handrail tubing is fed through a bath of molten zinc. A thin layer of zinc alloys with steel forms a metallurgical bond, providing long-term corrosion protection. Excess zinc is removed from the steel after it has been taken from the bath using a mechanical wiper, air knife, or steam. This results in a somewhat thin zinc galvanized coating. The benefits of inline galvanizing include fast processing times and consistent coating thicknesses. The major disadvantages of inline galvanizing are the high initial costs and the need for a specialized facility.
The Performance of Pre-Galvanized Pipe
The pre-galvanized pipe can also be galvanized to EN 10240 utilizing an automated technique. Immersion times are quite brief, and steam may be pushed through the bore of the tube after extraction to provide an acceptable surface finish. Although the coating thickness can reach 45-55 m, the majority of the product produced has a much thinner coating of 20-30 m.
Because pre-galvanized pipe materials are normally only immersed in the galvanizing bath for a short period of time, the coating is rather thin. Hot-dip galvanization produces a thicker zinc coating than pre-galvanization, which provides better rust and corrosion protection, especially for pipes that are frequently used outside and exposed to snow, ice, rain, and salt.
The zinc coating on the steel sheet must be in accordance with ASTM A525 Grade G90 and G120. The combined zinc weight of the external and interior surfaces must range from 0.90 oz/sq ft (or 0.45 oz/sq ft each side) to 1.20 oz/sq ft (or 0.60 oz/sq ft each side). These coating weights do not apply to the welded area on the inside.
Zinc metal has been used for corrosion protection of steel handrail tubing for more than 100 years. Hot-dip galvanizing is the most widely used method of applying zinc to steel handrail tubing. In this process, the entire handrail tubing is dipped into a bath of molten zinc. A thin layer of zinc alloys with steel forms a metallurgical bond, providing long-term corrosion protection. The benefits of hot-dip galvanizing include low initial costs, long-term corrosion protection, and low maintenance costs. The major disadvantage of hot-dip galvanizing is that it can be difficult to achieve a consistent coating thickness on complex shapes. In addition, the process can be slow and expensive.
| Feature | Hot Dip Galvanization | Pre-Galvanizing |
| Coating Thickness | Thick coating with minimum average requirements of 45-85μm within BS EN ISO 1461 | The coating thickness may vary, but it is typically circa 20μm for sheets and 20-30μm for tubes |
| Coating Continually | Continuous coating over the whole object | The uncoated area at cut edges |
| Coating Bond | Strong metallurgical bond with the base steel | Strong metallurgical bond with the base steel |
| Coating Formability | Forming after hot dipped galvanizing is not advised as it may damage the coating | A thin coating may be normally formed without any damage |
| Coating Appearance | Normally bright, but can be variable | Normally bright |
| Abrasion Resistance | A thicker layer of hard zinc-iron alloy gives a high resistance to abrasion | Thin alloy layer with reduced resistance to abrasion |
| Sacrificial Protection | Offer the highest level of sacrificial protection | Reduced sacrificial protection due to thin layer coating and at some uncoated areas (cut edges) |
