Insulated pipes must undergo acceptance inspection upon arrival at the construction site, prior to installation. However, due to limited on-site conditions, it is not feasible to conduct the full suite of tests performed in a laboratory. So, what checks can actually be performed on-site?
First is the verification of documentation. This includes the product certificate of conformity, factory inspection report, quality assurance certificate, and material specifications. Reputable manufacturers test every batch for properties such as density, thermal conductivity, closed-cell content, and outer casing wall thickness before shipment; these reports should be provided with the goods. Contracts can also include clauses stipulating random on-site sampling for independent testing.
Second is a visual inspection. Visually inspect the outer casing for obvious defects such as scratches, cracks, dents, or bubbles. According to the GB/T 29047 standard, the outer casing should be free of significant defects. The condition of the waterproof end caps-checking if they are intact or have detached-can also be directly observed on-site. The foam layer at the pipe ends must also be inspected for damage, moisture, or discoloration.
Next is dimensional measurement. Use a tape measure or caliper to measure the outer diameter, wall thickness, and the length of the exposed pipe end (reserved length). The insulation layer thickness should be measured at four points around the pipe end (top, bottom, left, and right) and averaged. Spot checks on the outer casing wall thickness are also necessary, as insufficient thickness compromises the pipe's compressive strength and waterproofing capabilities. The reserved length at the pipe end must meet standard requirements, typically a minimum of 150 mm.
While foam density and closed-cell content cannot be precisely measured on-site, a preliminary assessment can be made using simple methods. Press the foam at the pipe end by hand to gauge its density and check for any softness or sponginess. Observe the cross-section of the foam to see if the cells are uniform and fine, or if there are obvious voids or large, coarse cells. Although these are subjective assessments, experienced inspectors can identify numerous issues this way.
On-site acceptance inspection serves as the final checkpoint for quality control. Once the pipes are buried, it is too late to rectify problems. Although the scope of on-site inspection is limited, performing these checks thoroughly can at least filter out products with obvious defects.