Evaluation of atmospheric exposure test on structural steel coated with different materials in the east of Thailand

The environment has a significant impact on the corrosion of steel. Corrosion is unavoidable; however, the rate of corrosion can be minimized by painting and galvanizing. The rate of corrosion depends on the coating and the environmental condition. The purpose of this research is to study and evaluate different types of structural steel coated with different materials in the East of Thailand. The atmospheric corrosion test is conducted for two types of steel, SS400 and SM490 with six different coating systems which are bare steel, hot-dip galvanized steel, hot-dip galvanized with painting (duplex system), common base practice paint steel, well base practice paint steel, and the premium base paint steel and the location of atmosphere corrosion test is conducted in three test site which is at Chachoengsao, Chonburi, and Rayong.Following the ASTM G50 standard, specimens are exposed to the real environment for three months, six months, and one year at the desired location. Weathering station at the test site collects and monitors environmental data such as temperature, rainfall, and relative humidity on a daily basis but the SO2 pollution, and airborne chlorides on a monthly basis. The weathering stations are present only at Station 13 Chachoengsao and Station 14, Chonburi. The sulfur dioxide was collected through a lead dioxide cylinder and the chloride was collected through the dry gauze method. The exposed steel specimen for bare steel and Hot dip galvanized are cleaned and the corrosion products are removed. After analyzing the thickness loss data of the specimens, we are able to predict the thickness loss of the specimens for bare steel and hot-dip galvanized steel and using the environmental parameters and the thickness loss data of one year we are able to predict first-year corrosion based on environmental parameters. The painted specimens are analyzed, and we can evaluate and compare different types of paint-coated specimens using the data. The results would indicate how the environmental parameters affect corrosion rate and able us to compare structural steel with various coatings. The results can be used to choose a coating, predict the steel’s service life, and predict thickness loss.

环境对钢材的腐蚀具有显著影响。腐蚀虽无法避免，但可通过涂装与热浸镀锌（hot-dip galvanized）工艺将腐蚀速率降至最低。腐蚀速率取决于涂层类型与环境条件。本研究旨在针对泰国东部地区，对采用不同涂层材料处理的各类结构钢开展研究与评估。本次大气腐蚀试验选用SS400与SM490两种钢材，搭配六种涂层体系：裸钢、热浸镀锌钢、热浸镀锌+涂装双涂层体系（duplex system）、普通底涂涂装钢、优良底涂涂装钢及高级底涂涂装钢；试验点位设于差春骚府、春武里府与罗勇府三处。本次试验遵循ASTM G50标准，将试样置于上述试验点位的真实环境中分别暴露3个月、6个月与1年。试验点位的气象站每日采集并监测温度、降雨量与相对湿度等环境参数，每月监测二氧化硫（SO2）污染与大气氯化物含量数据。仅差春骚府13号试验站与春武里府14号试验站设有气象监测站。二氧化硫采用二氧化铅柱法采集，大气氯化物则采用干纱布法采集。裸钢与热浸镀锌钢的暴露试样需经清洁处理以去除表面腐蚀产物。通过分析试样的厚度损失数据，可预测裸钢与热浸镀锌钢试样的厚度损失；结合环境参数与1年期厚度损失数据，还可基于环境参数预测钢材的首年腐蚀情况。针对涂装试样，通过分析相关试验数据可对不同涂层涂装的试样进行评估与对比。研究结果可阐明环境参数对腐蚀速率的影响规律，并实现不同涂层结构钢的性能对比。该成果可用于遴选合适的涂层方案、预测钢材服役寿命以及预估厚度损失。