First, in the design and construction, we must really understand that the direct burial laying of heating pipelines can be divided into compensated direct burial laying and non-compensated direct burial laying. We must control the working principles, characteristics and application sites of the two methods, so as to make rational selection in design and safe, reliable and economical construction.

1．要控制概念：有補(bǔ)償直埋敷設(shè)方式，是經(jīng)過管線自然補(bǔ)償和補(bǔ)償器（如方形和波紋管補(bǔ)償器）來處理管道熱伸長量的，從而使熱應(yīng)力為*小；無補(bǔ)償直埋敷設(shè)，簡單地說就是管道在受熱時沒有任何補(bǔ)償措施，而是靠管材自身強(qiáng)度來吸收熱應(yīng)力。

1. First of all, we should control the concepts: there is a compensated direct burial laying method, which is to deal with the thermal elongation of pipeline by natural compensation and compensator (such as square and bellows compensator), so that the thermal stress is * small; non-compensated direct burial laying simply means that the pipeline does not have any compensation measures when heated, but relies on the pipe itself. Body strength absorbs thermal stress.

2．無補(bǔ)償敷設(shè)方式的根本原理：在裝置管道時，給管道加熱到一定溫度，然后將管道焊接固定，當(dāng)管道恢復(fù)到裝置溫度時（溫度降低），管道預(yù)先接受了一定的拉應(yīng)力。當(dāng)管道通熱工作時，隨著溫度的升高，管道應(yīng)力為零，當(dāng)繼續(xù)升溫時，管道的壓應(yīng)力增加，當(dāng)溫度升到工作溫度時，管道的壓應(yīng)力（熱應(yīng)力）仍小于許用應(yīng)力。這樣，管道能夠不用補(bǔ)償安裝而正常工作了。這種無補(bǔ)償方式應(yīng)用第四強(qiáng)度理論，施工時需求對管道預(yù)熱，施工比擬費事，但國內(nèi)外已有大量工程理論，理論計算牢靠，能確保平安。另一種無補(bǔ)償方式是近幾年由我國北京煤氣熱力設(shè)計院提出的計算辦法和應(yīng)力分類采用安定性剖析，應(yīng)用第三強(qiáng)度理論。這種方式充沛發(fā)揮鋼材塑性潛力，施工便當(dāng)，無需預(yù)熱。

2. The basic principle of non-compensated laying method: when installing pipeline, heating pipeline to a certain temperature first, then welding and fixing pipeline, when the pipeline restores to the installation temperature (temperature decreases), the pipeline accepts a certain tensile stress in advance. When the pipeline is heated, with the increase of temperature, the stress of the pipeline is zero. When the temperature continues to rise, the pressure stress of the pipeline increases. When the temperature rises to the working temperature, the pressure stress (thermal stress) of the pipeline is still less than the allowable stress. In this way, the pipeline can work normally without compensation installation. This non-compensatory method applies the fourth strength theory, which needs to preheat the pipeline during construction. It is difficult to compare the construction. However, there are a lot of engineering theories at home and abroad. The theoretical calculation is reliable and can ensure safety. Another non-compensatory method is the stability analysis and the third strength theory for the calculation method and stress classification proposed by Beijing Gas Thermal Design Institute in recent years. In this way, the plastic potential of steel can be fully developed, and the construction is convenient without preheating.

3．兩種敷設(shè)埋設(shè)深度思索不同要素。

3. Consider the different elements of two laying depths.

（1）當(dāng)肯定采用有補(bǔ)償直埋敷設(shè)方式時，埋設(shè)深度只思索由于空中荷載的作用不會毀壞管道的穩(wěn)定便可，從經(jīng)濟(jì)、施工便當(dāng)?shù)确矫嫠妓鳌．?dāng)采用有補(bǔ)償直埋敷設(shè)方式時，盡量淺埋，普通覆土厚度大于0．6米即可，且與管徑大小無關(guān)。

(1) When compensated direct burial is definitely adopted, the burial depth only considers that the stability of pipeline will not be destroyed due to the action of air load, and considers from the aspects of economy and construction convenience. When compensated direct burial is adopted, shallow burial should be used as far as possible. The thickness of common overlying soil is more than 0.6 meters, and it has nothing to do with the diameter.

（2）當(dāng)采用無補(bǔ)償直埋敷設(shè)方式時，埋設(shè)深度要思索管道的穩(wěn)定請求，穩(wěn)定性主要與覆土厚度有關(guān)，普通比有補(bǔ)償埋得深，當(dāng)采用不預(yù)熱的無補(bǔ)償直埋敷設(shè)管道時，*小覆土深度應(yīng)按《城市熱網(wǎng)設(shè)計標(biāo)準(zhǔn)》（CJJ34-90）第7．2．15條執(zhí)行，覆土厚度應(yīng)與管徑大小成正比。

(2) When using non-compensated direct burial method, the burial depth should consider the stability requirements of pipelines. The stability is mainly related to the thickness of overlying soil, which is generally deeper than that with compensation. When using non-preheated direct buried pipelines without compensation, * the depth of small overlying soil should be in accordance with Article 7.2.15 of the Urban Heat Network Design Standard (CJJ34-90). The thickness of the overlying soil should be proportional to the diameter of the pipe.

4．設(shè)計中終究采用無補(bǔ)償敷設(shè)還是有補(bǔ)償敷設(shè)方式，準(zhǔn)繩是直管道較長，中間分支較少，供熱介質(zhì)不超越100℃時，應(yīng)優(yōu)先選用無補(bǔ)償敷設(shè)方式，否則，應(yīng)思索有補(bǔ)償敷設(shè)方式。詳細(xì)的熱網(wǎng)主干線應(yīng)采用無補(bǔ)償敷設(shè)方式，而分支庭院管網(wǎng)則應(yīng)采用有補(bǔ)償敷設(shè)方式，但目前有的設(shè)計者偏愛有補(bǔ)償敷設(shè)，應(yīng)倡導(dǎo)優(yōu)化設(shè)計。

4. In the design, the non-compensated laying or compensated laying should be adopted eventually. The criterion is that the straight pipeline is longer, the middle branches are fewer, and the non-compensated laying should be preferred when the heating medium does not exceed 100 C. Otherwise, the compensated laying method should be considered. Detailed heat network trunk lines should be laid without compensation, while branch courtyard pipeline networks should be laid with compensation. However, the current designers prefer to lay with compensation, and should advocate optimal design.

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