DL/T 794-2012 in English

1 Scope

This standard specifies the technical requirements, quality index and test methods for chemical cleaning of fossil plant
This standard is applicable to chemical cleaning of the scale and corrosion products on the metal surface of thermal equipment made of iron and its alloys and that of the boiler of fossil fired generator units and steam powered equipment with the boiler outlet pressure not less than 3.8MPa.

2 Normative References

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the normative document (including any amendments) applies.
GB 8978 "Integrated Wastewater Discharge Standard"
GB/T 4334 "Corrosion of Metals and Alloys - Test Methods for Intergranular Corrosion of Stainless Steels"
GB/T 12145 "Quality Criterion of Water and Steam for Generating Unit and Steam Power Equipment"
GB/T 15970 "Corrosion of Metals and Alloys-Stress Corrosion Testing"
DL/T 522.1 "Determination of Acetoxime (DMKO) in Water"
DL/T 523 "Practice Evaluation and Testing Method of Inhibitors for Chemical Cleaning"
DL/T 561 "Guide for Chemical Supervision of Water and Steam in Thermal Power Plants"
DL/T 956 "Guide for Lay-up of Thermal Power Equipment in Fossil Fuel Power Plant"
DL/T 977 "Managerial Regulations for Enterprise Undertaking Chemical Cleaning of Thermal Equipment in Power Plant"
HG/T 2387 "Chemical Cleaning Quality Code for Industrial Facility"

3 General Provisions

3.1 The chemical cleaning for boiler adopts the cleaning process to clean the inner surface of the boiler heating surface and form the good passivating film on the metal surface through the chemical reaction of the corrosion products, deposit and pollutants in the chemical agent water solution and boiler vapor system. The chemical cleaning is the necessary measures to protect the heating surface against the accidents due to the corrosion and scaling and one of the effective measures to improve the boiler thermal efficiency and the unit vapor quality.
3.2 The organization responsible for the chemical cleaning of fossil plant shall be qualified in accordance with DL/T 977 and the cleaning without certificate is strictly forbidden.
3.3 The cleaning scheme and measures shall be established by the professionals, examined by the technical director and submitted and approved by the supervisor. The chemical cleaning of the boiler shall be supervised by the technical division; thereafter, the cleaning quality shall be inspected and evaluated.
3.4 The project director, technical director and laboratory personnel in the cleaning organization shall be certified to take the post after being trained and passing the assessment and the operation without certificate shall be strictly forbidden. Prior to the cleaning, the personnel involved in the chemical cleaning shall be subjected to the technical and safety education so that they are familiar with the cleaning system and master the safety operation procedure.

Foreword I
1 Scope
2 Normative References
3 General Provisions
4 Technical Requirements
5 Determination of Chemical Cleaning Conditions
6 Design and Installation of Chemical Cleaning System
7 Technological Process of Chemical Cleaning
8. Disposal of Liquid Waste after Cleaning
9. Quality Index for Chemical Cleaning
10. Chemical Supervision in Chemical Cleaning
11. Safety and Quality Assurance Measures
Appendix A (Normative) Methods of Water-cooled Wall Tube Cutting and Small-scale Test
Appendix B (Informative) Discharge and Disposal of Liquid Waste during Boiler Cleaning
Appendix C (Normative) Product Quality Criteria and Inspection Methods on Chemicals for Cleaning (including Acid, Alkali, Inhibitor and Passivant)
Appendix D (Informative) Scale Dissolving Capacity of Common Cleaning Medium
Appendix E (Informative) Calculation of Material, Equipment and Chemicals in Cleaning System
Appendix F (Normative) Method for Evaluation Test after Chemical Cleaning
Appendix G (Informative) Test Methods Used in Chemical Cleaning