METHOD STATEMENT FOR HYDROSTATIC TEST DURING WINTER SEASON

◎祁迎春

METHOD STATEMENT FOR HYDROSTATIC TEST DURING WINTER SEASON

◎祁迎春

随着“走出去”“走进去”国家战略的实施，众多的国内电建公司承接到国外电站项目，尤其是‘一带一路’上的优质项目。本文以哈萨克斯坦冬季高寒地带进行的水压试验为实际案例进行注意事项的论述以及关键点的安排，为类似的项目执行提供参考。

As more and more Chinese companies have signed and will execute the power plant projects overseas， it is very challenging to perform the work especially to have the hydraulic test in winter Season of rough area， this paper illustrate the typical example successfully demonstrated in this case.

1.Scope of Hydro-Test

The average temperature in China north areas during Winter season is relative lower than other areas， where the lowest temperature in record is -38℃ in the most rough days， therefore，there must be special measures to prepare and execute to control work quality and safety as well as to protect the boiler system and equipment after Hydro-Test.

This method described as follows will introduce the general measures and solution to conduct Hydro-Test in winter season， which is normally applicable to the construction work to be executed in China north areas in Winter season.

2.Construction conditions

analysis

The prefabricated panel materials will be normally used for the boiler building and turbine house， while the indoor temperature is rather difficult to control due to the freezing cold weather and big heat emission from windows and doors even possible air leakage.

On the other hand， it shall be also necessary to consider and take considerate measures to prevent any freezing and corrosive occurrence after the Hydro-Test in the roughly cold days， which will impact the normal schedule of boiler operation due to the heavy working loads to keep insulation and top sealing after the test.

Conclusively， the Hydro-Test to be conducted according to the Project Schedule through winter season will create challenging risks in safety for boiler equipment and pipes， by contrary， the subsequent construction work even normal operation will be delayed in schedule if postpone the Hydro-Test.

3.Preparation works before HyDro-Test

3.1 General Working Procedures for Boiler Hydro Test

The overall Air Tight Test shall be arranged and conducted for the whole boiler hydro system to test and clear all the possible defects existing in welding seams， piping and sealing， whereafter the boiler equipment shall be insulated properly.

The heating surfaces in boiler top and sealing shall be insulated and executed finally after the Hydro-Test to discover the potential quality defect and remedy the defects prior to Hydro-Test.

3.2 Temperature Analysis and Heating Energy Calculation

According to the temperature records of these 3 months in last year of local area， the average temperature and lowest temperature could be calculated，and then calculated the indoor requested temperature and heating load comparing with requested temperature design pressure.

Based upon the calculation and analysis， it shall be confirmed to decide the necessity of installation of additional heating facilities to preventany freezing damages when the boilers are not operating neither considering the heating emission from equipment and process pipes， temporary heating estimation.

3.2.1 Light Tube Heaters will be additionally installed around ash silos， horizontal SH in end shafts and horizontal RH to improve and maintain the temperatures inside boiler.

3.2.2 Coke furnaces will be arranged in boiler building elevation 0m and will be put into use when the temperature falling down -20℃ or the indoor temperature is lower than 5℃.

3.3 Typical HSE Control Points

HSE team will coordinate with construction boiler team to have full and overall inspections of boiler parts and equipment， and conduct the safety training and explanation to all the team members attending the Hydro Test.

HSE team shall arrange appointed personnel to observe the weather condition and checkthe extreme cases in history record.

HSE team will make earlier preparation for counter measures to cope with any error or fault in boiler start-up or site blackout or personnel shifts changing.

3.4 Temporary Protective Measures

Based upon the analysis of local history weather record in local area and monitor the recent weather conditions on site， HSE team and boiler construction team will inspect the overall enclosing and capping conditions again in boiler buildings， such as main gates， windows & doors， flue ducts and air duct inlets， etc.

3.5 Ambient Temperature Observing Work

Observing points will be installed properly in boiler elevation 0m， 18m，57m， 62m to observe the ambient temperature prior to the normal activities of Hydro Test to select the most suitable time to start Hydro Test.

4.PROCESS CONCTROL DURING HYDRO-TEST

4.1 Scope of Hydro-Test

This preliminary system including feeding pipes， economizer， water wall， start-up system， SH and boiler drainage， sampling， air discharging，Nitrogen system.The Reheating Steam system including LTRH， HTRH and attemperator， drainage， air discharging pipes.

4.2 Environment Temperature Observation

According to boiler design， there are none down headers and water discharging in Platen superheater，secondary superheater and vertical reheater， so the water from Hydrotest could not be drained completely from such said areas， therefore， the temperature in tubes， furnace and flue ducts of such heating surfaces will be concentrating observation to control the temperature again any freezing， the temperature shall be more than 5 ℃.

During the preparation stage before test， the indoor temperature in Boiler Building shall be heated up， and HSE team will organize to carefully check every position for the possible air and steam leakage， and ensure that the indoor temperature could be increased gradually and maintained well in the temperature ranges as required， refer to the temperature Curve as follows：

4.3 Temperature Maintaining for Test Water

The temperature control for test water to be pumped to the boiler tubes is the key of overall hydro test.

The tubes of all heating surfaces shall be kept in the ranking of 21℃ -70℃， therefore， the test water shall be controlled in the range of 70℃ -80℃when pumping the feeding up to boiler during hydro test process.

The boiler will be water flushed to clean all the foreign items and subject to inspection and acceptance. Condensing water makeup tank will be pumped full of water， and start heating procedure to control the heating temperature less than 90℃， Meanwhile， chemicals ammonia and acetaldoxime will be injected in ratio to take the sampling mixture subject to test acceptance for its concentration. The condensing water pump will be started up to feed the water to boiler， adjusting the pump recycle opening to keep the desal water flow at the current of 70t/h，maintaining the water tanks operating in higher water level with accepted chemical concentration.

The boiler inside water shall be maintained warmly ranking 25℃ -45℃ for the sake of requirement from metal tubes and for the convenience of manpower inside inspection. The water will be drained utilizing the highest point of discharging valve in bulging system to exchange the hot desal water.

Boiler water in the whole bulging system shall be calculated every hour during the lower pressure stage according to Boiler Water Pressure Curve， then ensure that each part of heating surfaces shall be raised up 35℃-40℃ to satisfy all the tube walls in the bulging system be kept accepted temperature.

The coke furnaces shall be put into use to present any impact from the ambient environment when its temperature lower than 7℃ in boiler elevation 0m， which is very critical to maintain boiler ambient temperature higher than 5℃ and water in tubes are higher than 21℃.

5.Protective measure post Hydro-test

Proper and compete protection measure shall be taken after the Hydro Test considering the continuous freezing weather conditions in the job site until March， therefore， the feeding water to boiler shall be heated and kept recycling， minimum recycle 1 time when the environment temperature falling down -25℃ and control the boiler tube temperature no lower than 8℃， surely the water could be changed to present any freezing as per the tube conditions.

The quantity of coke furnaces could be adjusted according to the weather conditions outdoor and boiler enclosing conditions to keep the boiler indoor temperature over 0℃ after the Hydro Test.

（作者单位： 中国机械工业建设集团有限公司 ）