The coating scheme for anti-corrosive spiral steel pipes is determined by the operating environment.

The three-layer polyethylene (3PE) coating system combines epoxy powder, an adhesive layer, and a polyethylene layer to form a structurally stable protective barrier.

Epoxy coal tar coating involves the alternating application of epoxy coal tar paint and glass fiber cloth, creating a water- and corrosion-resistant coating system. Internal cement mortar lining forms a smooth inner surface on the pipe wall, helping to reduce flow resistance.

Epoxy powder coating utilizes high-density polyethylene as a base material, balancing mechanical strength with corrosion resistance. Each process has its own specific advantages; the appropriate method should be selected based on the conveyed medium and installation conditions.

Anchor bolts typically have two main dimensions: diameter and length.

Diameter: The diameter of an anchor bolt refers to the thickness of its threaded shaft, usually measured in inches or millimeters. Standard anchor bolts range in diameter from ¼ inch to 1.5 inches.

Length: The length of an anchor bolt refers to the overall length of the bolt, including the threaded shaft and the embedded portion, and is measured in inches or millimeters. Anchor bolts typically range in length from 2 inches to 18 inches.

The selection of anchor bolt size depends on several factors, including the intended application, load requirements, and anchoring material.

Light responsibility applications: For lightweight fixtures, such as bathroom fixtures, electrical boxes, or small shelves, anchor bolts with a diameter of ¼ inch or 5/16 inch are generally sufficient for 2 to 4 inches.

Medium responsibility applications: For heavier fixtures, such as cabinets, electrical appliances, or larger racks, it is generally recommended to use anchor bolts with a diameter of 3/8 inch or 1/2 inch and a length of 4 to 6 inches.

Heavy-duty applications: For securing heavy machinery, structural beams, or foundation components, anchor bolts with a diameter of ¾ inch or larger are typically required to be 6 to 18 inches.

Factors affecting anchor bolt selection:

Several additional factors need to be considered when selecting anchor bolts: Material: Anchor bolts are available in various materials, including steel, stainless steel, and concrete screws. Material selection depends on the specific application and environmental conditions.

Basic materials: The type of anchoring material, such as concrete, masonry, or wood, will also affect the selection of anchor bolts and their installation method.

1. Non-fixed length (standard/random length). This refers to product dimensions (length or width) that fall within the range specified by standards but do not require a specific, fixed size. Metal materials delivered under this classification need only fall within the prescribed length range. For example, for ordinary round steel with a diameter of 25mm or less, the standard length range is 4–10m; therefore, any round steel within this range is acceptable for delivery.

2. Fixed length. This refers to material cut to a specific, fixed dimension as required by the order. When delivered as fixed-length material, the metal must match the exact length specified by the buyer in the contract. For instance, if the contract specifies a fixed length of 5m, all delivered material must be exactly 5m long; lengths shorter or longer than 5m are considered non-compliant. However, since it is practically impossible for every piece to be exactly 5m, standards permit a positive deviation but prohibit any negative deviation.

3. Multiple length. This refers to material cut to an integer multiple of a fixed dimension specified in the order. When delivered as multiple-length material, the length must be an integer multiple of the base length (single length) specified by the buyer (plus the allowance for saw cuts). For example, if the buyer specifies a single length of 2m, a double length would be 4m and a triple length would be 6m, with the addition of one or two saw-cut allowances, respectively. Saw-cut allowances are defined in the standards. For multiple-length deliveries, only positive deviations are permitted; negative deviations are not allowed.

4. Short length. This refers to material with a length below the minimum limit of the standard non-fixed length range but above the absolute minimum permissible length. For example, standards for steel pipes used for water and gas transport allow a batch to contain up to 10% (by piece count) of short-length pipes measuring 2–4m. Here, 4m is the lower limit of the non-fixed length range, and 2m is the minimum permissible length.

5. Narrow width. "Narrow-width stock" refers to material with a width below the minimum specified for random-length/random-width stock but not less than the minimum permissible width. When supplying such material, one must adhere to the standards regarding the allowable proportion of narrow-width pieces and the absolute minimum width.

Fixed-length seamless steel pipes: "Fixed-length" refers to pipes delivered at specific lengths requested by the user. The purchaser specifies the exact length in the contract, and the manufacturer processes and cuts the seamless pipes to those dimensions. The advantages of fixed-length pipes include uniform length, which facilitates subsequent installation, fit-up, and welding while reducing the need for on-site cutting; they are ideal for projects with precise length requirements, such as pipeline prefabrication and structural support applications. Due to the precision processing and material loss involved, their price is typically slightly higher than that of random-length products.

Random-length (or variable-length) steel pipes: This term refers to pipes delivered within a standard length range rather than at a single, fixed value. Delivery is usually based on a specific length interval, with actual lengths varying within that range. Production of random-length pipes offers greater flexibility and higher material utilization rates, and they are generally more cost-effective; they are suitable for applications where length requirements are less strict and on-site cutting is feasible.

Purchasers can make a choice based on project needs: fixed-length pipes are preferable for projects requiring minimized on-site processing and high installation efficiency, whereas random-length pipes are more suitable for scenarios with flexible length requirements where cost control is a priority.