Structural Steel Tube & Pipe used for any permanent or temporary construction projects shall be manufactured in accordance with one of the following methods:
- Allied’s triple layer Flo-Coat tubing
- Pre-galvanized tube
- Schedule 40 hot dip galvanized pipe
The specifications for the three most common types of galvanized tube and pipe are detailed below:
Allied Flo-Coat Tube: Cold Formed, High Frequency Welded and Hot Dip Galvanized
Tube shall be manufactured using steel conforming to the requirements of ASTM A1008/A1008M and A1011/A1011M with a typical minimum yield strength of 30,000 psi. The steel shall be cold formed and welded into tube utilizing the high frequency induction welding process capable of forming a weld bead stronger than the parent metal. The tube shall be subsequently passed through a molten zinc bath capable of applying the required exterior zinc coating thickness. Depending on the tube size and gauge, the mechanical properties of the finished tube shall have a minimum yield strength of 50,000 psi and a minimum tensile strength of 55,000 psi.
The tube exterior surface shall consist of three complementary coatings: a lead-free zinc coating, conversion coating to inhibit white rust; and a clear organic polymer coating as a final barrier to corrosion.
The combined corrosion resistance of these three coatings shall have the ability to last up to 1000 hours of exposure to salt spray fog (ASTM B117) without exceeding a maximum of 5% red rust. The tube interior surface shall be 100% coated after welding with a zinc rich organic coating.
Pre-Galvanized Tube: Cold Formed and High Frequency Welded Pre-Galvanized Steel Strip
The tube shall be manufactured from pre-galvanized steel conforming to ASTM A446. The coated steel shall be cold formed and welded into tube utilizing the high frequency induction welding process capable of forming a weld bead stronger than the parent metal. The outside coating damaged during welding shall be repaired by metallizing (spraying molten zinc wire). The inside weld area damaged during welding shall be left unprotected.
The zinc coating on the steel sheet shall conform to ASTM A525 Grade G90 and G120. The exterior and interior surface shall have a combined zinc weight ranging 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 inside welded area.
Schedule 40 Pipe, Hot Dip Galvanized
This type of pipe is not covered by any specification, although the outside diameter and the wall thickness are defined by other specifications for pipe that is not galvanized. Schedule 40 pipe is typically hot formed and butt welded, or cold formed and high frequency welded.
After being formed into a pipe and cut, individual lengths of pipe are immersed into a molten zinc bath (usually containing lead) until the desired zinc coating weight is achieved. The finished pipe typically has a total zinc weight for both ID and OD combined of 1.8 oz/sq ft. Since there are no specifications for this type of pipe, galvanizing is usually performed per ASTM A123.
The mechanical properties of this type of pipe varies according to the method of manufacturing. However, the typical yield strength is around 30,000 psi.
|Flo-Coat Process/Gatorshield||Hot-Dip (Schedule 40)||Pre-Galvanized|
|Exterior Corrosion Resistance||Excellent||Good||Fair|
|Interior Corrosion Resistance||Excellent||Good||Poor|