Before using the heat shrink sleeve, it is necessary to preheat the steel pipe. The general preheating temperature is 70-90 degrees Celsius.

The pre-heating of the patch can be flame heating or electric induction heater. Flame requirements for different pipe diameters: the diameter of the pipe is less than or equal to 450mm, medium-strength flame or electric induction heater is used, and the minimum torch specification is 150000Btu / hr (1Btu = 1.055kj). The pipe diameter is greater than or equal to 450mm, using medium to strong flame heaters or electric induction heaters, and the minimum torch specification is 300000Btu / hr. When the pipe diameter is greater than or equal to 760mm, an electric induction heater or infrared heating device is used. Of course, many on-site construction is not so good, generally we recommend the liquefied gas baking gun for preheating.

      There are two main purposes for preheating. One is to remove the humidity on the surface of the steel pipe, because if there is moisture, if it is not removed, after the epoxy primer is applied, the moisture will form a layer of the membrane, which may cause the primer to come off. The second is that there will be a certain temperature on the surface of the steel pipe after preheating. This temperature will cause the epoxy primer to react chemically and slowly cure before the heat shrink tape and heat shrink sleeve can be installed.

      Before sandblasting and derusting the surface, we should preheat the steel pipe of the repaired part to a temperature of at least 30 degrees Celsius or 40-50 degrees Celsius above the dew point, which can be adjusted appropriately according to the ambient temperature. Celsius, the preheating temperature at the mouth should be increased to more than 70 degrees Celsius.

热缩套补口施工前的预热

补口热缩套使用前，都需要对钢管进行预热，一般预热的温度在70-90摄氏度。

补口预热可以采用火焰加热，也可采用电感应加热器进行预热。不同管径补口时的火焰要求：管径小于等于450mm，采用中等强度的火焰或电感应加热器，最小火炬规格150000Btu/hr(1Btu=1.055kj)。管径大于等于450mm，采用中到强的火焰加热器或电感应加热器，最小火炬规格300000Btu/hr。当管径大于等于760mm时，采用电感应加热器或者红外线加热设备。当然很多在现场施工没有那么好条件，一般我们都推荐液化气烤枪进行预热。

     预热主要是有两个目的，一是除去钢管表面的湿度，因为如果有水分，没有除去的话，涂刷环氧底漆后，水分会形成一层隔膜，导致底漆可能会脱落。二是预热后钢管表面会有一定温度，这个温度会使环氧底漆起化学反应，慢慢固化，然后才能安装热缩带与热缩套。

     我们在进行表面喷砂除锈前，应将补口部位的钢管预热至露点以上至少30摄氏度的温度或者40-50摄氏度，可以根据环境温度适当调节，如果遇到大风或环境温度低于15摄氏度，应将补口处的预热温度提高到70摄氏度以上。