According to whether the temperature of the overall pipeline welding is equal to the temperature of backing, the installation method can be divided into:
Cold Installation
The temperature of the overall pipeline welding is equal to the temperature of backing.
The installation processes of the pipeline welding and groove backfill are finished in the cold condition. In the cold ambient temperature, the pipeline is in zero stress state. In running condition, the stress and internal force of anchorage section and the displacement of compensation device in the sliding section are a bit large because the rising temperature is large.
It can backfill timely during the pipeline construction. It can save large quantity of money because it maximum reduce of even no need to install compensator and fixed support. But the pipeline stress and internal force increase, sometimes it’s necessary to strengthen the tee or increase the embedding depth.
Prestress Installation
The temperature of the overall pipeline welding is higher than the temperature of backfilling.
Prerelease the thermal expansion deformation from ambient temperature to preheating temperature. when the pipeline temperature returns to the ambient temperature, the pipeline is in the tensile stress station to make a prestressing effect. In running condition, because of prerelease of some thermal expansion deformation and the stress and internal force of anchorage section, the displacement of compensation device in the sliding section have a large degree of decline.
According o the sequencing of the pipeline welding and trench backfill, the prestress installation can be divided into preheat installation method and one-time compensator installation method.
Preheat Installation Method
Preheat the pipeline before backfilling, when the pipeline is heated to he preheat temperature, then weld th pipeline and backfill. In the preheat installation method, the release of thermal deformation is under the condition of the groove exposure. It can make immediate uniform distribution of prestressing effect in the pipe section.
One-time Compensator Installation Method
Preheat the pipeline after backfilling, installing one-time compensator in the pipeline to absorb thermal deformation from ambient temperature to expected preheating temperature. After teh pipeline welding, other grooves can be backfilling except the pipeline near the one-time compensator. In the process of first time heating, when the one-time compensator compensation dimension is reaching the thermal deformation prereleased at the compensation section, this one-time compensator can be welded to realize the whole pipeline welding.
In the one-time compensator, installation method, the thermal deformation prerelesed is under the condition of groove backfilled. The release of thermal deformation will be limited by the soil friction. The actual preheat temperature of welding one-time compensator is higher than expected preheat temperature, and only through times of temperature changing can make an effect of uniform distribution of prestressing effect for the whole pipeline.
All in all, compared with cold installation, the fixed pier thrust and compensator compensation dimension fo prestress installation will decline, but the stability of whole and partial pipeline will improve.