SRTP Pipe

High-Density Polyethylene (HDPE): HDPE pellets are the primary plastic material. They are first loaded into a hopper and dried thoroughly to remove any moisture. Moisture can cause voids and weaknesses in the final product.

Steel Strips: High-quality steel coils of a specific thickness and grade are used. The steel strip is often pre-coated with a special adhesive resin. This adhesive is crucial for creating a strong chemical bond between the steel and the HDPE during the fusion process.

The flat steel strip is uncoiled and fed into a forming machine.

Profiling: The strip passes through a series of precision rollers that cold-form it into a specific profile, typically a "V" or "U" shape. This shape is engineered to provide maximum structural reinforcement.

Winding: The profiled steel strip is then wound helically (spirally) to form a continuous cylindrical "skeleton" or cage. This skeleton will become the reinforcing core of the pipe.

A simplified diagram showing the steel strip being shaped.

Two separate extruders work simultaneously to melt the HDPE pellets and extrude them into a molten state.

Inner Layer Extruder: This extruder produces a smooth, continuous tube of molten HDPE that will form the pipe's inner wall.

Outer Layer Extruder: This extruder produces the molten HDPE that will encapsulate the steel skeleton and form the corrugated outer wall.

This is the most critical stage where the steel and plastic are combined into a single, integrated structure.

Assembly: The helical steel skeleton from Step 2 moves into a specialized composite die head.

Encapsulation:

The molten inner HDPE tube is fed into the center of the steel skeleton.

Simultaneously, the molten outer HDPE is extruded over the outside of the steel skeleton.

Molding & Fusion: The entire assembly (inner PE, steel skeleton, outer PE) immediately enters a corrugator or forming machine. This machine consists of a series of moving mold blocks that are shaped like the pipe's outer profile.

Vacuum pressure is applied through the mold blocks, pulling the molten outer HDPE tightly against the steel skeleton and into the corrugated shape of the molds.

The heat and pressure cause the inner and outer HDPE layers to fuse together through the gaps in the steel skeleton. This process completely encapsulates the steel, protecting it from the environment and locking it into place. The pre-applied adhesive on the steel ensures an inseparable bond.

A cross-section view of the forming process where PE encapsulates the steel rib.

As the newly formed pipe exits the corrugator, it is still hot and malleable. It immediately passes through a cooling section.

Water Spray/Bath: The pipe is sprayed intensively with cool water or submerged in a water bath.

Solidification: This rapid cooling solidifies the HDPE, setting the pipe's final shape and dimensions and ensuring its structural integrity.

Haul-off Machine: A caterpillar-style haul-off machine grips the pipe and pulls it along the production line at a constant, controlled speed. This speed must be perfectly synchronized with the extrusion rate to maintain consistent wall thickness and dimensions.

Planetary Cutter: A planetary saw or cutter moves along with the pipe as it travels. Once the desired length (e.g., 6 or 12 meters) is reached, the saw makes a clean, precise, and perpendicular cut without interrupting the continuous production process.

The finished pipe sections undergo rigorous quality checks before being approved for shipping.

Visual Inspection: Checking for any surface defects, blemishes, or inconsistencies.

Dimensional Checks: Verifying the inner and outer diameter, wall thickness, and corrugation profile against specifications.

Physical Testing:

Ring Stiffness Test: This is a crucial test to confirm the pipe can withstand the designed external loads.

Impact Test: To ensure durability during handling and installation.

Bonding Test: To verify the strength of the bond between the steel and the HDPE.

Marking: The pipe is printed with essential information, including its size, material grade, pressure rating, manufacturing standard, and production date.