NB/T 10857-2021Code for design of rational service life and durability for hydropower projects (English PDF)

Foreword

This document was issued on 22 December 2021 by the National Energy Administration of the PRC and takes effect on 22 June 2022.

It is a NB/T standard: recommended rather than compulsory, but it is the text a Chinese reviewer applies when assessing a submission.

It is classified under ICS 27.140, Chinese classification P59.

This code was formulated in accordance with the requirements of the Notice of the National Energy Administration on Issuing the 2015 Plan for the Formulation (Revision) of Energy Sector Industry Standards (Guo Neng Ke Ji [2015] No. 283). The drafting group carried out extensive investigation and research, carefully summarized practical experience, referred to relevant domestic standards and widely solicited opinions before formulating this code.

The main technical contents of this code are: general provisions, terms, basic requirements, rational service life and design service life, durability design requirements, construction requirements, and operation and maintenance requirements.

This code is under the administration of the National Energy Administration; it was proposed by and its routine management is the responsibility of China Renewable Energy Engineering Institute, and the Energy Sector Standardization Technical Committee on Hydropower Survey and Design (NEA/TC 15) is responsible for the interpretation of its specific technical contents. Comments and suggestions arising during implementation should be sent to China Renewable Energy Engineering Institute (address: No. 2 Liupukang Beixiaojie, Xicheng District, Beijing; postcode: 100120).

Chief development organizations: PowerChina Kunming Engineering Corporation Limited; China Renewable Energy Engineering Institute.

Participating development organizations: PowerChina Northwest Engineering Corporation Limited; PowerChina Beijing Engineering Corporation Limited; PowerChina Chengdu Engineering Corporation Limited; PowerChina Zhongnan Engineering Corporation Limited.

Chief drafting staff: Zhang Zongliang, Wang Fuqiang, Deng Liangjun, Zhang Manman, Wang Yiming, Dang Lincai, Wang Xiaodong, Liu Yaolai, Yan Lei, Wu Mingxin, Yang Yunsheng, Wang Weiguo, Lu Chao, Zhao Shiming, Wu Xiaoyu, Fei Binghong, Lu Junmin, Cui Zhi, Ran Congyong, Zhang Congmao, Yu Jianqing, Xiang Hong, Li Peng, Zhan Chenhui.

Chief reviewers: Li Sheng, Yang Zeyan, Lu Mingzhi, Wu Guanye, Lu Zhongmin, Li Yonghong, Wang Guojin, Hu Xiaoyun, Li Shisheng, Wu Yajun, Zhan Zhenggang, Wang Junli, Zhou Yuefei, Zhang Sherong, Du Xiaokai, Jiao Pengcheng, Xu Lili, Li Guangwei.

Announcement of the National Energy Administration

National Energy Administration Announcement No. 6 of 2021: in accordance with the Standardization Law of the People's Republic of China and the Measures for the Administration of Energy Standardization, the National Energy Administration approved 356 energy industry standards, including the Code for Design of Forced Permeability Enhancement Engineering in Underground Coal Mines (Annex 1), and 25 foreign-language editions of energy industry standards, including the Technical Code for Design and Calculation of Combustion System of Fossil-fired Power Plant (Annex 2), and hereby releases them.

Annex 1 (List of Industry Standards) lists this code as item 8: NB/T 10857-2021, Code for Design of Rational Service Life and Durability for Hydropower Projects, with no superseded standard and no adopted international standard; approval date 2021-12-22, implementation date 2022-06-22.

The code was prepared under the chief editorship of China Renewable Energy Engineering Institute, approved by the National Energy Administration, published by China Water and Power Press (Beijing, 2022) and put into effect on 22 June 2022.

1 Scope

NB/T 10857-2021 is the Chinese code for setting the rational service life of hydropower structures and designing them for durability. A dam, a powerhouse and a tunnel are expected to last far longer than most civil works, but the environment they sit in attacks them continuously - water flowing at high velocity, freeze and thaw, sulphate and magnesium in groundwater, carbonation, abrasion by sediment. The code first fixes how long each structure must last, by project grade and by the importance of the component, and then what the design must do so that it does. It sets the general provisions and defined terms, then the basic requirements: the classes of service life with the tables assigning them to dams, spillways, intakes, powerhouses, tunnels and their components, and the classification of the exposure environment by the aggressiveness of water and soil, with tabulated limits for sulphate, magnesium, pH and other indicators. Durability design follows for concrete - minimum strength grade, maximum water-cement ratio, minimum cement content, cover to reinforcement, crack width limits, frost resistance and impermeability grades, and additional measures for severe environments - and for steel structures, metal gates and embedded parts with their corrosion protection. Requirements on construction quality, inspection, maintenance and the assessment of existing structures close the code.

1.0.1 This code is formulated to standardize the design of rational service life and durability of hydropower projects, to ensure the quality of engineering design, and to meet the requirements of safety and reliability, economic rationality and technical advancement.

1.0.2 This code is applicable to the determination of the rational service life and to the durability design of new hydropower projects.

1.0.3 The rational service life and durability requirements of reconstructed and extended hydropower projects shall be studied and demonstrated.

1.0.4 The design documents of each design stage of a hydropower project shall state the rational service life of the project and of its hydraulic structures.

1.0.5 When a hydropower project has reached its rational service life, or has been damaged by an accident or disaster, and is to remain in use, an assessment of its safety and service performance shall be carried out and its continued service life shall be determined.

1.0.6 In addition to this code, the design of rational service life and durability of hydropower projects shall also comply with the current relevant national standards.

2 Terms

2.0.1 hydropower project; hydropower engineering; hydroelectric project: a project whose main task is hydroelectric power generation, including pumped storage power stations, which may also serve flood control, irrigation, water supply, navigation and other tasks as required.

2.0.2 hydraulic structure: a structure that controls and regulates water flow, develops and utilizes water resources, prevents water hazards and achieves the objectives of the hydropower project. By period of use, hydraulic structures are divided into permanent hydraulic structures and temporary hydraulic structures; by their function in the hydropower project, they are divided into main structures and secondary structures.

2.0.3 structure and component: the continuous parts of a hydraulic structure that have a certain strength and stiffness and are organically combined together. The physically distinguishable parts of a structure are components.

2.0.4 rational service life: the minimum required number of years during which a hydropower project and its hydraulic structures, after completion and commissioning, can be used safely according to their design functions under normal operating conditions and specified maintenance conditions.

2.0.5 design service life: the period specified in the design during which a structure or component can be used for its intended purpose without major repair.

2.0.6 structure durability: the ability of a structure to maintain its serviceability and safety within the rational service life under the environmental actions determined in the design and the specified maintenance and use conditions.

2.0.7 maintenance: technical, management and other activities undertaken to maintain the functions required of a structure or its components within the design service life, including upkeep and restoration.

2.0.8 restoration: activities carried out by patching, replacement or strengthening to restore a damaged structure or its components so as to meet normal use. According to the scale and cost of the restoration and its effect on the normal use of the structure, restoration may be divided into major repair and minor repair. Restoration that requires the normal use of the structure to be stopped for a certain period, or requires large-area replacement of damaged material in structural components, or replacement of main structural components, is major repair.

2.0.9 chlorine ion diffusion coefficient: a parameter describing the diffusion of chloride ions in concrete pore water from a zone of high concentration to a zone of low concentration.

2.0.10 alkali content: the sum of the products of the mass of each raw material in a unit volume of concrete, such as cement, mineral admixture, chemical admixture, water and sand and stone aggregates, and its effective alkali content, expressed in kg per cubic metre. The effective alkali content is the content of alkali in the concrete raw materials that can take part in the alkali-aggregate reaction, expressed as equivalent Na2O, that is, the Na2O content plus 0.658 times the K2O content, expressed in %.

2.0.11 water to binder ratio of concrete: the mass ratio of the water content to the total amount of cementitious materials in a concrete mixture.

2.0.12 cementitious material: a material which, through its own physical and chemical action during the transition from a plastic paste to a hard stone-like body, can bind granular or lump materials into a whole. In concrete or mortar it is the general term for cement and mineral admixtures.

2.0.13 concrete with high-volume supplementary cementitious materials: concrete whose cementitious materials contain a relatively large proportion of mineral admixtures and blended materials such as fly ash, silica fume and ground slag, and which requires a relatively low water to binder ratio.

2.0.14 concrete cover reinforcement: the minimum distance from the concrete surface to the outer edge of the outermost reinforcement (including longitudinal bars, stirrups and distribution bars); for post-tensioned prestressing tendons, the distance from the outer edge of the duct or hole to the concrete surface.

2.0.15 additional protective measures: supplementary measures taken to further improve the durability of concrete structures on the basis of conventional means such as improving concrete compactness, increasing cover thickness and using waterproofing and drainage measures, including concrete surface coatings, anticorrosion surface layers, epoxy-coated reinforcement, reinforcement corrosion inhibitors and electrochemical corrosion protection.

2.0.16 air-entraining concrete: concrete in which an air-entraining agent is incorporated to improve its durability and rheological properties.

3 Basic Requirements

3.1.1 The rational service life of a hydropower project and its hydraulic structures shall be determined according to the rank of the project and the grade of the structures.

3.1.2 The design service life of the structures of hydraulic buildings shall be determined according to the rational service life of the building, the importance of the structure, the replacement conditions and the inspection and repair conditions.

3.1.3 The durability design of the structures of hydraulic buildings shall be carried out according to the design service life and the environmental category in which the structure is located.

3.1.4 Structural design shall determine the materials, detailing, construction technical requirements and protective measures according to the different environmental categories, and shall set out the operation and maintenance requirements.

3.1.5 In chloride environments such as seawater, salt spray and deicing salt, the durability design of the main structures of buildings shall be based on analysis and study of the grade of the building, the natural environmental conditions, the construction and operating conditions, the consequences of damage and the difficulty of maintenance, and durability technical requirements shall be put forward.

3.1.6 When new technologies, new processes, new equipment and new materials are adopted in durability design, experimental research and demonstration shall be carried out.

3.2.1 The environmental categories in which hydraulic concrete structures are located may be divided into 5 categories according to the mechanism of corrosion of the structural materials, and shall be determined according to Table 3.2.1 (Environmental categories of hydraulic concrete structures).

Table 3.2.1, category 1: indoor dry environment.

Table 3.2.1, category 2: outdoor exposed environment; indoor humid environment; environment permanently underground or under fresh water.

Table 3.2.1, category 3: fresh water level fluctuation zone; mildly corrosive environment; underwater seawater environment; environment affected by deicing salt; saline soil environment.

Table 3.2.1, category 4: marine atmospheric zone; seawater level fluctuation zone; light salt spray zone; environment subject to deicing salt action; moderately corrosive environment.

Table 3.2.1, category 5: seawater splash zone and tidal zone; heavy salt spray zone; strongly corrosive environment.

Note 1 to Table 3.2.1: the boundary between the atmospheric zone and the splash zone is the design highest water level plus 1.5 m; the boundary between the splash zone and the water level fluctuation zone is the design highest water level minus 1.0 m; the boundary between the water level fluctuation zone and the underwater zone is the design lowest water level minus 1.0 m.

Note 2 to Table 3.2.1: the heavy salt spray zone is the onshore outdoor environment within 50 m of the high tide line; the light salt spray zone is the onshore outdoor environment from 50 m to 500 m from the high tide line.

Note 3 to Table 3.2.1: an environment affected by deicing salt is an environment affected by deicing salt spray; an environment subject to deicing salt action is an environment splashed by deicing salt solution.

Note 4 to Table 3.2.1: for buildings in category 3 and category 4 environmental conditions where freeze-thaw action is relatively severe, the environmental category may be raised by one category.

3.2.2 When the environmental water in which a structure is located is chemically corrosive, the contents of bicarbonate ion (HCO3-), sulfate ion, magnesium ion and CO2 in the water and the pH value of the water should be measured, and the degree of chemical corrosion should be determined according to these contents and the acidity range of the water. The criteria for corrosion by environmental water shall comply with Table 3.2.2 and with the following provisions:

3.2.2 item 1: the site shall be a region without alternate wetting-drying or freeze-thaw action, or a semi-humid or humid region with alternate wetting-drying or freeze-thaw action. Where the site is an arid or semi-arid region with alternate wetting-drying or freeze-thaw action, or a high cold region at an elevation above 3000 m, special demonstration shall be carried out.

3.2.2 item 2: where concrete bears water pressure on one side and is exposed to the atmosphere on the other, the ratio of the maximum acting hydrostatic head to the concrete wall thickness shall be greater than 5.

3.2.2 item 3: the impermeability grade of the concrete used in concrete buildings shall not be lower than W4, and the water to binder ratio shall not be greater than 0.6.

3.2.2 item 4: concrete buildings shall not be in direct contact with pollution sources. The direct corrosive action of pollution sources on concrete shall be specially studied.

Table 3.2.2 (Criteria for corrosion by environmental water), decomposition class, leaching type, criterion HCO3- content in mmol/L: no corrosion when HCO3- is greater than 1.07.

Table 3.2.2, leaching type: weak corrosion when HCO3- is not greater than 1.07 and greater than 0.70.

Table 3.2.2, leaching type: moderate corrosion when HCO3- is not greater than 0.7.

Table 3.2.2, leaching type: strong corrosion — no limit specified.

Table 3.2.2, decomposition class, general acid type, criterion pH value: no corrosion when pH is greater than 6.5.

Table 3.2.2, general acid type: weak corrosion when pH is not greater than 6.5 and greater than 6.0.

Table 3.2.2, general acid type: moderate corrosion when pH is not greater than 6.0 and greater than 5.5.

Table 3.2.2, general acid type: strong corrosion when pH is not greater than 5.5.

Table 3.2.2, decomposition class, carbonate type, criterion aggressive CO2 content in mg/L: no corrosion when CO2 is less than 15.

Table 3.2.2, carbonate type: weak corrosion when CO2 is not less than 15 and less than 30.

Table 3.2.2, carbonate type: moderate corrosion when CO2 is not less than 30 and less than 60.

Table 3.2.2, carbonate type: strong corrosion when CO2 is not less than 60.

Table 3.2.2, decomposition-crystallization composite class, magnesium sulfate type, criterion magnesium ion content in mg/L: no corrosion when the magnesium ion content is less than 1000.

Table 3.2.2, magnesium sulfate type: weak corrosion when the magnesium ion content is not less than 1000 and less than 1500.

Table 3.2.2, magnesium sulfate type: moderate corrosion when the magnesium ion content is from 1500 to less than 2000.

Table 3.2.2, magnesium sulfate type: strong corrosion when the magnesium ion content is not less than 2000.

Table 3.2.2, crystallization class, sulfate type, criterion sulfate ion content in mg/L: no corrosion when the sulfate ion content is less than 250 for ordinary cement, or less than 3000 for sulfate-resisting cement.

Table 3.2.2, sulfate type: weak corrosion when the sulfate ion content is not less than 250 and less than 400 for ordinary cement, or not less than 3000 and less than 4000 for sulfate-resisting cement.

Table 3.2.2, sulfate type: moderate corrosion when the sulfate ion content is not less than 400 and less than 500 for ordinary cement, or not less than 4000 and less than 5000 for sulfate-resisting cement.

Table 3.2.2, sulfate type: strong corrosion when the sulfate ion content is not less than 500 for ordinary cement, or not less than 5000 for sulfate-resisting cement.

3.2.3 When a structural component is subject to the combined action of several environmental categories, the durability requirements under the individual action of each environmental category shall be met separately.

3.2.4 For dam concrete and other hydraulic structural concrete subject to weathering and freeze-thaw action, the frost resistance grade shall be clearly specified. The frost resistance grade requirements shall comply with the relevant provisions of the current industry standard Code for Design of Hydraulic Structures against Ice and Freezing Action NB/T 35024.

3.2.5 When the environmental water is aggressive to hydraulic concrete, the anti-aggression design of the concrete shall be carried out according to the type and degree of aggression of the environmental water.