Acid Cleaning Procedure [PDF]

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Piping guidelines Part I



No.:



PG W722/02/006



Piping design, Attachment V



Index:



b



Acid Cleaning Procedure



Page:



1 of 6



Attachment to Piping Guidelines Chemical Cleaning Process for Combined Cycle Power Plant



Table of Contents



1



SYSTEMS TO BE CLEANED.................................................................................................................................2



2



PREPARATION OF PIPING SYSTEM FOR CLEANING PROCESSES.........................................................2 2.1 2.2



3



Chemical Cleaning with Hydrofluoric Acid (Acid Cleaning)............................................................................2 Chemical Cleaning with Ammonia-EDTA (Acid Cleaning)...............................................................................4



CONNECTION BETWEEN PERMANENT AND TEMPORARY PIPES.........................................................5 3.1 3.2



Connection by flange..........................................................................................................................................5 Connection by Welding.......................................................................................................................................6



Siemens AG . Power Generation



H30-K5014 Anweisung/Richtlinie, engl. 2001-01 D97



The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.



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Piping guidelines Part I



No.:



PG W722/02/006



Piping design, Attachment V



Index:



b



Acid Cleaning Procedure



Page:



2 of 6



Chemical Cleaning Process for Combined Cycle Power Plant



1



Systems to be cleaned All lines and any other systems to be flushed and chemically cleaned are indicated in the P& I diagram “General flow diagram for chemical cleaning”, prepared for each project. In general HP, IP, LP and Condensate Pre-heater (optional), system is flushed and subsequently chemically cleaned (Acid Cleaning). Cooling Water System (PGB, PCB) is cleaned only by circulating method and other water systems (PAB, GHC, GKB etc.) are cleaned by flushing.



2



Preparation of Piping system for Cleaning Processes After the hydro test has been done for the system, the system is connected by means of temporary pipes to create a close circuit through which the water can be circulated. Also the temporary pipes and its connections are tested to detect any leakage to the ambient or adjacent systems. Connection of main piping system to the temporary one is generally flanged for easy removal. For high pressure systems the connection can be welded too. There are two methods generally followed to chemically clean the pipe:1) Chemically cleaning the pipe with Hydrofluoric acid. 2) Chemically cleaning the pipe with Ammonia-EDTA solution. Chemicals like Tri-sodium phosphate, Caustic soda or similar high alkaline agents are never used for the surface preparation.



2.1



Chemical Cleaning with Hydrofluoric Acid (Acid Cleaning) The following procedure of the chemical cleaning is in accordance with German VGB Guideline VGB-R 513 and is also known as Circulating Method. Always de-mineralized water is used to flush or clean the system. For circulation temporary pumps are used. For flushing; if required, temporary pumps can be used. The waste water after flushing is collected in a suitable storage facility (e.g. temporary holding pit) and then disposed off. Description of Cleaning Steps: 



First flushing The first step after filling of the water steam cycle and performance of the leakage test shall be flushing of the system with de-mineralized water to remove loose dirt such as globules, sand or other particles and in order to prepare the inner surfaces for following acid cleaning steps. The flushing of the sections to be cleaned shall be executed with the maximum possible flow rate. The minimum velocity of the flow shall be 0.5 m/s in each part of the system and 1 m/s in vertical pipes with flow going upwards.



Siemens AG . Power Generation



H30-K5014 Anweisung/Richtlinie, engl. 2001-01 D97



The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.



/conversion/tmp/scratch/357816080.doc



Piping guidelines Part I



No.:



PG W722/02/006



Piping design, Attachment V



Index:



b



Acid Cleaning Procedure



Page:



3 of 6



Flushing is performed without circulation. Prior to the following step the system is drained completely. 



Treatment with wetting agent The pretreatment with wetting agent has the aim to transform the often hydrophobic surface into a hydrophilic state. This step is made so efficient that proper surface preparation is achieved within approx three hours. The stage shall be executed by the circulating method. Prior to the following step the system shall be drained completely.







Second flushing By flushing with de-mineralized water the wetting agent and loosened dirt will be washed out of the system. The flushing of the sections to be cleaned shall be executed with the maximum possible flow rate. The minimum velocity of the flow shall be 0.5 m/s in each part of the system and 1 m/s in vertical pipes with flow going upwards. Flushing is performed without circulation. Prior to the following step the system is drained completely.







Preheating After the second flushing all sections are heated to a temperature between 50 oC and 70oC in the cleaning loop in order to have a high efficiency of the hydrofluoric cleaning. Preheating is done by circulation through an external, temporary heating facility or steam generated by the auxiliary boiler. Prior to the following step the system is drained completely.







Cleaning with Hydrofluoric acid This step will be executed with a solution of approx. 1 % hydrofluoric acid together with inhibitor at a temperature between 50oC and 70oC. The velocity of the cleaning solution shall not exceed 0.5 m/s in order to avoid erosion and excessive metallic decay. For that purpose the required quantity of concentrated hydrofluoric acid will be injected together with the inhibitor into the actual cleaning circuit during constant circulation by using a temporary dosing pump.







Third flushing Use of nitrogen to purge the acid solution prior to flushing and passivation is recommended. The acid solution is drained and the system flushed with de-mineralized water.



Siemens AG . Power Generation



H30-K5014 Anweisung/Richtlinie, engl. 2001-01 D97



The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.



/conversion/tmp/scratch/357816080.doc



Piping guidelines Part I



No.:



PG W722/02/006



Piping design, Attachment V



Index:



b



Acid Cleaning Procedure



Page:



4 of 6



The flushing of the sections which have been chemically cleaned shall be executed with the maximum possible flow rate. The minimum velocity of the flow shall be 0.5 m/s in each part of the system and 1 m/s in vertical pipes with flow going upwards. Flushing is performed without circulation. Prior to the following step the system is drained completely. 



Alkalization and Passivation The pH value of circulating de-mineralized water is increased to 10.2 by dosing ammonia. After proper distribution (Check pH-value) hydrogen peroxide is added to the solution for passivation of the bare surface. Passivation is also performed in the circulation method by using the temporary circulation pump.







Inspection and Mechanical Cleaning All sections will be drained and inspected. The drums should be cleaned mechanically (only manually) if required. The condenser hot well should be mechanically cleaned if required. Suitable cleaning methods include manual cleaning and high pressure hydro cleaning.



2.2



Chemical Cleaning with Ammonia-EDTA (Acid Cleaning) The cleaning with Ammonia-EDTA solution is performed by circulation. Flushing is performed without circulation. Always de-mineralized water is used to flush or clean the system. For circulation temporary pumps are used. For flushing; if required, temporary pumps can be used. The waste water after flushing and rinsing is collected in a suitable storage facility (e.g. temporary holding pit) and then disposed off. Normally Chemical Cleaning with AmmoniaEDTA does not include an inhibitor.



Description of Cleaning Steps 



Flushing The first step after filling of the water steam cycle and performance of the leakage test shall be flushing of the system with de-mineralized water to remove loose dirt such as globules, sand or other particles and in order to prepare the inner surfaces for following acid cleaning steps. The flushing of the sections to be cleaned shall be executed with the maximum possible flow rate. The minimum velocity of the flow shall be 0.5 m/s in each part of the system and 1 m/s in vertical pipes with flow going upwards. Flushing is performed without circulation. Prior to the following step the system is drained completely.



Siemens AG . Power Generation



H30-K5014 Anweisung/Richtlinie, engl. 2001-01 D97



The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.



/conversion/tmp/scratch/357816080.doc







Piping guidelines Part I



No.:



PG W722/02/006



Piping design, Attachment V



Index:



b



Acid Cleaning Procedure



Page:



5 of 6



Preheating After the flushing all sections shall be preheated to a temperature of 120-200 o C (in no case 200° C shall be exceeded, as EDTA will then be thermally decomposed) in order to have a high speed of dissolution and high efficiency of Ammonia-EDTA. Preheating shall be done basically by circulation via external heating facility, which can be heated by means of steam, generated by the auxiliary boiler.







Cleaning with Ammonia-EDTA This step is executed with a solution of Ammonia-EDTA (typical concentration 1% -1.5 %) at a temperature of 140-160o C. The velocity of treating solution is ≤ 0.1 m/s. The required quantity of concentrated Ammonia-EDTA is injected into the actual cleaning circuit using a temporary dosing pump during constant circulation.







Rinsing The Ammonia-EDTA solution is drained and the system rinsed in order to remove residual cleaning solution to such extend that no later iron precipitation can occur.







Inspection and Mechanical Cleaning All sections are drained. The drums should be cleaned mechanically (only manually) if required.



The condenser hot well should be mechanically cleaned if required. Suitable cleaning methods include manual cleaning and high pressure hydro cleaning.



3 3.1



Connection between permanent and temporary pipes Connection by flange



Siemens AG . Power Generation



H30-K5014 Anweisung/Richtlinie, engl. 2001-01 D97



The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.



/conversion/tmp/scratch/357816080.doc



3.2



Piping guidelines Part I



No.:



PG W722/02/006



Piping design, Attachment V



Index:



b



Acid Cleaning Procedure



Page:



6 of 6



Connection by Welding



Siemens AG . Power Generation



H30-K5014 Anweisung/Richtlinie, engl. 2001-01 D97



The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved.



/conversion/tmp/scratch/357816080.doc