Advanced Water Management Centre, The University of Queensland, St. Lucia, Queensland 4072, Australia.
Advanced Water Management Centre, The University of Queensland, St. Lucia, Queensland 4072, Australia.
Water Res. 2015 Sep 1;80:30-40. doi: 10.1016/j.watres.2015.04.015. Epub 2015 May 6.
The development of concrete corrosion in new sewer pipes undergoes an initiation process before reaching an active corrosion stage. This initiation period is assumed to last several months to years but the key factors affecting the process, and its duration, are not well understood. This study is therefore focused on this initial stage of the corrosion process and the effect of key environmental factors. Such knowledge is important for the effective management of corrosion in new sewers, as every year of life extension of such systems has a very high financial benefit. This long-term (4.5 year) study has been conducted in purpose-built corrosion chambers that closely simulated the sewer environment, but with control of three key environmental factors being hydrogen sulfide (H2S) gas phase concentration, relative humidity and air temperature. Fresh concrete coupons, cut from an industry-standard sewer pipe, were exposed to the corrosive conditions in the chambers, both in the gas phase and partially submerged in wastewater. A total of 36 exposure conditions were investigated to determine the controlling factors by regular retrieval of concrete coupons for detailed analysis of surface pH, sulfur compounds (elemental sulfur and sulfate) and concrete mass loss. Corrosion initiation times were thus determined for different exposure conditions. It was found that the corrosion initiation time of both gas-phase and partially-submerged coupons was positively correlated with the gas phase H2S concentration, but only at levels of 10 ppm or below, indicating that sulfide oxidation rate rather than the H2S concentration was the limiting factor during the initiation stage. Relative humidity also played a role for the corrosion initiation of the gas-phase coupons. However, the partially-submerged coupons were not affected by humidity as these coupons were in direct contact with the sewage and hence did have sufficient moisture to enable the microbial processes to proceed. The corrosion initiation time was also shortened by higher gas temperature due to its positive impact on reaction kinetics. These findings provide real opportunities for pro-active sewer asset management with the aim to delay the on-set of the corrosion processes, and hence extend the service life of sewers, through improved prediction and optimization capacity.
新污水管道中的混凝土腐蚀在达到活跃腐蚀阶段之前经历一个起始过程。这个起始期被认为持续数月到数年，但影响这个过程及其持续时间的关键因素并没有被很好地理解。因此，本研究专注于腐蚀过程的这个初始阶段和关键环境因素的影响。这种知识对于新污水管道腐蚀的有效管理很重要，因为这种系统的每一年使用寿命延长都具有非常高的财务效益。这项为期 4.5 年的长期研究是在专门建造的腐蚀室中进行的，这些腐蚀室非常接近污水管道的环境，但控制了三个关键环境因素：硫化氢（H2S）气相浓度、相对湿度和空气温度。从工业标准污水管道上切割的新鲜混凝土试片被暴露在腐蚀性条件下，这些试片既暴露在气相中，也部分浸没在污水中。总共研究了 36 种暴露条件，通过定期取回混凝土试片进行详细分析表面 pH 值、硫化合物（单质硫和硫酸盐）和混凝土质量损失来确定控制因素。因此确定了不同暴露条件下的腐蚀起始时间。研究发现，气相和部分浸没试片的腐蚀起始时间都与气相 H2S 浓度呈正相关，但仅在 10 ppm 或以下的水平，这表明硫化物氧化速率而不是 H2S 浓度是起始阶段的限制因素。相对湿度也对气相试片的腐蚀起始起作用。然而，部分浸没试片不受湿度影响，因为这些试片直接与污水接触，因此有足够的水分使微生物过程进行。由于其对反应动力学的积极影响，较高的气体温度也缩短了腐蚀起始时间。这些发现为积极主动的污水资产管理提供了真正的机会，旨在通过提高预测和优化能力来延迟腐蚀过程的开始，从而延长污水管道的使用寿命。
