At present, both in China and abroad, the development of direct-buried laying technology for insulated pipelines has a history of more than 60 years. Direct-buried laying of heating pipelines generally adopts three laying methods: uncompensated laying, compensated laying, and one-time compensation laying. The media conveyed by heating pipelines can generally be divided into two types: high-temperature steam and hot water. Below Jinan Insulated Pipe Let us introduce the secrets behind it.
Uncompensated direct-buried laying method: In the direct-buried laying of heating pipelines, the friction between the soil and the outer surface of the insulated pipe is used to fix the pipeline. The entire pipeline does not need compensators or fittings that serve a compensating function. The plastic potential of the steel is fully utilized so that the pipeline forms a self-balanced state. The pipeline does not need to be preheated before the trench is backfilled.
Compensated direct-buried laying method: When the temperature of the medium conveyed by the pipeline is greater than or equal to 120°C, the plasticity of the steel is then insufficient for the pipeline to form a self-balanced state, and preheating of the pipeline cannot be implemented. Therefore, compensated laying should be adopted, and compensators and fixed piers need to be installed on the pipeline.
One-time compensation direct-buried laying method: This direct-buried laying method uses a one-time compensator to absorb part of the expansion of the pipeline in the preheated state during installation, thereby reducing thermal stress at the maximum service temperature. A one-time compensator means that during direct-buried laying, the compensator compensates once and, after being welded and fixed, becomes part of the pipeline. The one-time compensator shall be selected based on data such as pipeline length, spacing of fixed piers, thermal displacement of the pipeline, and the maximum compression of the compensator. Its compensation capacity shall be greater than the expansion of twice the friction length of the pipe section. Two compensators may be connected in series on a straight pipe section without a fixed pier in between. The one-time compensator requires insulation.
Practice has shown that for thermal pipelines of DN 500 or smaller, uncompensated direct-buried laying may be used. For thermal pipelines larger than DN 500, uncompensated cold installation can also be achieved by increasing wall thickness. For insulated pipes of DN 200 or larger, spiral-welded pipe of grade Q235B is generally used, and the thermal stress generated by heating of the pipe should not exceed the allowable stress. In the calculation, soil friction, elastic force, and the maximum installation length must be computed.
That concludes the common compensation methods for insulated pipelines. We hope it is helpful. For more information, please follow us. Jinan Insulated Pipe
