Direct-buried insulated pipes produced by black-jacketed insulated LSAW pipe manufacturers offer low prices and guaranteed quality, making them an excellent choice for heating-project users. Our company uses imported high-pressure complete PU foaming equipment to produce three-in-one direct-buried insulated pipes with excellent overall performance. We strictly implement rust removal on the outer surface of the steel pipe and corona treatment on the inner surface of the outer jacket, further improving the bonding performance of the insulated pipe. The insulation material is rigid PU foam with a density of 60 kg/m3 to 80 kg/m3, fully filling the gap between the steel pipe and the casing and providing a certain bonding strength so that the steel pipe, outer casing, and insulation layer form a firm composite. PU foam has good mechanical and thermal insulation properties; it can typically withstand 120°C, and through modification or combination with other insulation materials can withstand 180°C. Compared with various conventional insulated pipes, prefabricated direct-buried insulated pipe has outstanding advantages: excellent thermal insulation performance, heat loss of only 25% of conventional pipe, and long-term operation that can save substantial energy and significantly reduce energy costs.
Precautions for Prefabricated Direct-Buried Black-Jacketed Insulated Steel Pipe:
One must truly understand that direct-buried laying of heating pipelines is divided into two methods: compensated direct-buried laying and uncompensated direct-buried laying, in both design and construction. Truly master the working principles, characteristics, and application scenarios of each of the two methods, so that they can be reasonably selected in design and construction can be safe, reliable, and economical.
2. Carry out thorough inspection after arrival on site. Before construction, the manufacturer of prefabricated direct-buried insulated pipe must be investigated. Unqualified insulated pipe shall be rejected.
3. Welding of PU insulated pipe is a key task that ensures project quality in the construction of prefabricated direct-buried pipelines.
4. The construction quality of various chambers directly affects project quality and pipeline service life, as do fixed supports. Poor waterproofing of a chamber will damage components by water immersion. Construction shall therefore be carried out carefully to ensure quality.
5. When pressure-test conditions are to be met, pressure testing of prefabricated direct-buried insulated pipe must be taken seriously. First fill with water and vent the air, then proceed in two steps: no leakage within 10 minutes of holding pressure. Strength test: after raising the pressure in the pipe to 1.5 times working pressure, tap each weld around the weld with a 1 kg hammer. Tightness test: when the pressure is reduced to working pressure, 30 minutes with no leakage and a pressure drop not exceeding 0.2 atm is acceptable. Pressure-test records shall be kept as required by the code.
6. Because prefabricated direct-buried insulated pipe is buried underground, most of the work at project acceptance is concealed. If final acceptance is not thorough and as-built records are incomplete, subsequent use will be affected.
7. Joints and backfill shall be carried out only after pipeline pressure testing, as-built survey, and cleaning are complete. Sand of the specified thickness must be backfilled according to the construction characteristics of PU insulated pipe; cutting corners is strictly prohibited.
8. This must be given sufficient attention. Field joint insulation of prefabricated direct-buried insulated pipe may only be carried out after the pressure test has passed. Field joint insulation construction is unique to prefabricated direct-buried insulated pipeline construction; construction quality directly affects service life. The insulation layer has two methods: field foaming and insulation-tile construction. Whichever method is used, defects such as annular voids, cracking, and delamination must not occur. There are various methods for the protective layer (such as HDPE and FRP protective jackets), but the integrity, tightness, and waterproofing of the joint must be guaranteed. Slow rise of PU insulated pipe foam generally occurs in autumn and winter or during morning construction, caused by a sudden drop in temperature or low ambient temperature. This can be resolved by raising ambient temperature and black-component (isocyanate) temperature. Generally, raising the black-component temperature to 30–60°C and ambient temperature to 20–30°C is sufficient.
PU insulated pipe can be classified by laying method into PU direct-buried insulated pipe and overhead PU insulated pipe; by temperature of the conveyed medium into ambient-temperature, high-temperature, and cryogenic PU insulated pipe; by outer protective jacket into FRP-jacketed, HDPE-jacketed, and steel-jacketed PU insulated pipe, among others; and finally by conveyed medium into buried rigid PU foam anti-corrosion insulated pipe, steam direct-buried PU composite prefabricated insulated pipe, and high-temperature PU insulated pipe, among others.
