There's a saying in the insulated pipe industry: "Three parts product, seven parts construction." Straight pipe sections are manufactured in the factory, making quality relatively controllable. However, there are too many variables in the on-site construction process. Any oversight in any detail can turn a good pipe into a hidden danger. From actual engineering experience, the following stages are the most concentrated areas of problems:
The joint is the weakest link. The most vulnerable part of the entire insulated pipe is not the pipe body, but the joint where two pipes connect. Joints must be completed on-site, including welding the outer protective pipe, baking and sealing with heat-shrinkable tape, and on-site foaming. Construction conditions are far less controllable than in the factory. If the seal is not tight, groundwater or moisture will seep into the insulation layer. The main reasons for joint failure are improper construction and poor quality. The sealing performance of the outer protective layer of the joint decreases with service time. Once water enters, the polyurethane foam will hydrolyze and age, losing its insulation function, and may even powder and disappear. The pipe body will also suffer severe corrosion.
Welding quality is equally critical. Poor installation techniques for pipe joints and fittings, non-compliance with welding standards, and failure to perform flaw detection on welds as required are all common problems. Inadequate beveling before welding, failure to perform proper argon arc welding for the root pass, and defects such as missing filler metal, slag inclusions, pinholes, and insufficient thickness can all lead to insufficient weld strength. It's also common for welds to be submerged in water after only the root pass is completed. These welding defects can escalate into leaks or even pipe bursts during operation.
Backfilling and storage also frequently cause problems. Poor-quality backfill soil containing large foreign objects can puncture the outer sheath of the insulation pipe. If fine sand layers are not properly laid on both sides and above the pipe, and the original soil containing gravel is used directly for backfilling, the outer sheath is easily cracked. Storage is equally crucial; improper stacking of pipes and fittings can damage the insulation and corrosion protection layer, and unsealed pipe openings can allow debris and moisture to enter.
The impact of the construction environment cannot be ignored. Low ambient temperatures during winter construction can affect the quality of the joint insulation foam. Welding in low-temperature, snowy conditions requires the construction of windproof shelters, and the welding rods must be dried and heated. Ignoring these environmental factors makes it difficult to guarantee quality. Most problems in the construction of insulated pipes are concentrated in the stages of joint sealing, welding, backfilling, and storage. By paying close attention to these areas, the reliability of the pipeline network can be guaranteed.