Non-Destructive Testing of Technical Conditions of RC Industrial Tall Chimneys Subjected to High Temperature.

Farzat Askifi,Hala Hammadeh,Marek Maj,Andrzej Ubysz

doi:10.3390/ma12122027

Abstract

Non-destructive tests of reinforced concrete chimneys, especially high ones, are an important element in assessing their condition, making it possible to forecast their safe life. Industrial chimneys are often exposed to the strong action of acidic substances, They are negatively exposed to the condensation of the flue gases. Condensate affects the inside of the thermal insulation and penetrates the chimney wall from the outside. This is one reason for the corrosion of concrete and reinforcing steel. Wet thermal insulation settles, and drastically reduces its insulating properties. This leads to an increase in temperature in the reinforced concrete chimney wall and creates additional large variations in temperature fields. This consequently causes a large increase in internal forces, which mainly increase tensile and shear stresses. This results in the appearance of additional cracks in the wall. The acid condensate penetrates these cracks, destroying the concrete cover and reinforcement. Thermographic studies are very helpful in monitoring the changes in temperature and consequently, the risk of concrete and reinforcement corrosion. This simple implication between changes in temperature of the chimney wall and increasing inner forces as shown in this article is particularly important when the chimney cannot be switched off due to the nature of the production process. Methods for interpreting the results of thermovision tests are presented to determine the safety and durability of industrial chimneys.

Highlights

Industrial reinforced concrete chimneys are often exposed to a chemically aggressive environment.The combustion gases conveyed via the chimney undergo condensation inside it or are dissolved in precipitation, becoming strongly acidic liquids
The wall of a reinforced concrete chimney subjected to repeated wind and thermal loads behaves linearly
The maximum temperature gradient in the reinforced concrete shell in the winter season increased by about 420% in comparison with the gradient calculated for the worst insulation case

Summary

Introduction

Industrial reinforced concrete chimneys are often exposed to a chemically aggressive environment. The combustion gases conveyed via the chimney undergo condensation inside it or are dissolved in precipitation, becoming strongly acidic liquids. The two corrosion processes result in the rapid degradation of the chimney structure. One should bear in mind the high cost and the technological challenges involved in their construction and that they perform an essential role in the production processes and so cannot be put out of service for repairs. In steelworks and coking plants, the damping of the furnace from which the combustion gases are conveyed to a chimney results in the destruction of the whole power unit. Materials 2019, 12, 2027 current technical condition of the chimney and monitoring the degradation processes over its whole service life [1]

Causes and Effects of Reduced Effectiveness of Chimney Thermal Insulation

Thermographic Surveys of Chimney Thermal Insulation

Thermal and Static Load Analysis

Adopted Assumptions

Types of Thermal Effects in the Chimney

Distribution of Temperature in Chimney Wall for Undamaged Insulation

Surface Temperature Load

Increase in Bending Moments Due to the Increase in the Temperature Gradient

Conclusions

Findings

Model of influence damaged theundamaged undamaged area