What are the differences in design principles and connection methods between plastic-coated steel pipes

First, what are the design principles of plastic-coated steel pipes?

The design of plastic-coated steel pipes should comprehensively consider practicality, safety, reliability, and economy to select a suitable solution. Specific design and calculations should follow these principles:

1. Meet service life requirements. From the perspective of intended use, the service life of new steel pipes, especially plastic pressure pipes, should be considered first, rather than the allowable load. This is because pipelines are structural components, and the service life of plastic-coated steel pipes should be consistent with the service life of the building.

2. The inner diameter of the plastic-coated steel pipe must meet flow rate requirements. The inner diameter, flow rate, and flow velocity of plastic-coated steel pipes are closely related. While meeting flow rate requirements, the flow velocity should be selected to determine the inner diameter of the plastic-coated steel pipe.

3. The wall thickness of the plastic-coated steel pipe must meet pressure requirements. The rated pressure of a steel pipe is closely related to its wall thickness and the ring stress of the pipe itself. Once a plastic-coated steel pipe is selected, its ring stress is already determined, and the rated pressure depends only on its wall thickness. Therefore, the wall thickness of the plastic-coated steel pipe must meet the rated pressure requirements.

Second, what are the connection methods for plastic-coated steel pipes?

1. Cutting plastic-coated steel pipes: Plastic-coated steel pipes should be cut using a metal saw. For large-diameter pipes, a sawing machine is recommended. When using a disc cutter, the rotation speed should not exceed 800 r/min. The cut section of the steel pipe should be perpendicular to the pipe axis.

2. Preparations before connecting plastic-coated steel pipes:

1) After cutting, the ends of the plastic-coated steel pipe should be smoothed with a fine file to remove any burrs.

2) A special reamer should be used to chamfer half the thickness of the plastic coating layer, with a chamfer angle of 10°-15°.

3) If the coating of the plastic-coated steel pipe is intact at the end, it should be chamfered inwards using a cutting tool. If the end of the plastic-coated steel pipe is damaged, it must be repaired (using repair fluid) until the coating is completely crack-free.

4) After grooving, the plastic coating on the protruding part of the groove will be damaged and must be repaired until the coating surface is smooth and completely free of cracks and damage.

5) Cleaning should be done using cotton scraps and a brush to remove oil, water, and metal shavings from the pipe ends and inside the plastic-coated steel pipe.

3. Connection Methods of Plastic-Coated Steel Pipes

1) Threaded Connection: Threading should be done using an automatic threading machine, following current national standards.

2) Flange Connection

Single Installation Method: On-site measurement and drawing of a single-line pipeline processing diagram are performed. After processing, coating, and lining, the pipe is transported to the site for installation.

Two-Step Installation Method: On-site welding of uncoated/unlined steel pipes and fittings with flanges is used to assemble the pipeline. Then, the pipe is disassembled for coating and lining before being transported to the site for installation.

Grooved connections: Pre-made grooved plastic-coated pipe fittings should be used preferentially; the grooves should be pressed using a dedicated grooving machine, and the groove depth should meet relevant standards.