Please discuss the purging and testing of medium and high-pressure steam pipelines in turbines

Someone once posted on the forum: Steam purging. The steam systems in chemical plants usually have multiple pressure level parameters to meet the requirements of different equipment and process conditions. For example, there is low-pressure steam used for mixing and heating, medium-pressure steam used for heating, in direct process applications, and in industrial turbines, as well as high-pressure steam used to drive large industrial turbines. Especially regarding the steam pipes used to drive industrial turbines, during steam purging it is necessary not only to remove any dirt and debris from the pipes but also to eliminate the rust on the metal surfaces, as such substances, if carried along by the high-speed steam flow, can cause severe damage to the rapidly rotating turbine blades. Therefore, it is very important to properly master the steam purging method and adhere to strict quality requirements. Steam purging is usually carried out in two categories – high, medium, and low pressure – based on the operating parameter range of the pipelines (there are also three categories: high, medium, and low pressure), and the requirements for purging vary among these categories. (1) Source and parameter selection of purge steam. To improve purging efficiency and reduce purging costs, steam system purging is usually carried out using reduced-pressure purging, but the steam consumption remains high, typically requiring 50-70% of the steam flow rate within the pipes at their rated load. High parameters (medium pressure, high temperature), long duration. Therefore, the purging of steam pipelines is mostly carried out simultaneously with the startup of their feed steam boilers. In the steam generators (waste heat boilers) of chemical plants, such as those for ethylene and synthetic ammonia production, where high-temperature process gas is used, external steam is generally employed or steam is supplied by a startup boiler built within the plant itself in order to shorten the commissioning time, before chemicals are introduced into the plant. The requirements for the steam source in steam purging are that its steam parameters (pressure, temperature) and steam volume must be sufficient to meet the purging needs of the steam pipelines at various pressure levels. Steam parameters are the main factors that directly affect the purging effect. Steam purging utilizes the energy (also known as momentum) generated by the flow of steam within the pipe to wash away rust and debris inside it; the greater the energy, the better the effect. The factors that affect the energy of the steam medium during purging include: the steam parameters during purging (pressure, temperature) ； Hydraulic characteristics of steam pipes ； The degree of opening of the main valve during purging, etc. In fact, these three factors are interrelated, and it is necessary to select appropriate purging parameters based on the specific circumstances. The principle for selecting steam purging parameters is to ensure that the momentum of the steam inside the pipe during purging (also known as blowing) is greater than that at the rated load; in other words, the purging coefficient at any point in the system to be cleaned must be greater than 1. That is, the purging coefficient k = (flow rate of purging steam)² * specific heat capacity of steam at the area to be purged / [（flow rate of steam at rated load）² * specific heat capacity of steam under rated conditions]. Typically, when using steam for purging, the steam flow rate inside the pipes is set at 50–70% of the rated value; therefore, the pressure of the steam source and the superheating temperature of the steam during purging can be calculated by using the reference calculation methods based on the parameters of the purging steam, in combination with the hydraulic characteristics of the pipe section being purged. Generally, the flow velocity of the purge steam in pipes at different pressure levels is set as follows: High-pressure steam pipes (4–12 MPa) ≥ 60 m/s; Medium-pressure steam pipes (1–4 MPa) ≥ 40 m/s; Low-pressure steam pipes (

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A shooting plan prepared by me for reference: Steam purging (shooting) plan for hydrogen production units 1. Purpose and scope of purging 1.1 Purpose of purging To remove various debris remaining in the superheater system and steam pipes during manufacturing, transportation, storage, and installation (such as sand particles, stones, swarf, iron oxide scale, etc.), prevent tube failures in the superheaters and damage to the flow components of the turbine during operation, enhance the safety and efficiency of the unit, and improve the quality of steam during operation. Blowing out steam pipes is commonly known as target shooting. 1.2 Main scope of the blowing pipe 1.2.1 Boiler superheaters and their systems. 1.2.2 Main steam pipes 2. Quality standards for tube cleaning and parameter selection 2.1 Quality standards for tube cleaning According to the specifications, the tube cleaning coefficient for each section of the superheater and its pipelines should be greater than 1 ； A target plate is installed inside the temporary exhaust pipe at the end of the purging pipe (or at the exhaust outlet); this target plate can be made of aluminum, with a width of approximately 8% of the inner diameter of the exhaust pipe, and its length extends across the entire inner diameter of the pipe ； On the condition that the blowing tube system is functional, two consecutive replacements of the target plate for inspection are carried out; the particle size of the impact marks on the target plate shall be no larger than 0.8 mm, and no more than 8 visible marks shall be present, which determines that the cleaning process is successful. 2.2 Selection of blowpipe parameters 2.2.1 The blowpipe coefficient is calculated using the following formula: Blowpipe coefficient = (steam flow rate during blowpipe operation)² × (specific volume of steam during blowpipe operation) / (steam flow rate at rated load)² × (specific volume of steam at rated load) 2.2.2 The superheater and its steam piping system in the boiler must meet the following requirements during cleaning. 2.2.2.1 The cross-sectional area of all temporary pipes shall be greater than or equal to that of the pipe being cleaned, and the temporary pipes should be as short as possible to reduce resistance. 2.2.2.2 The blowpipe coefficient at all locations in the purging system shall be greater than 1. 3. Blowpipe method and techniques 3.1 Blowpipe method A one-step blowpipe method is employed. 3.2 Blowpipe Method There are two basic methods for steam blowpipe cleaning: pressure-stabilized blowing ； Pressure-reducing purging. Since the device is in operation, a pressure-stabilizing blowpipe is used. The duration for which the blowpipe control valve remains fully open each time mainly depends on the medium-pressure balance. After one blowdown process is completed, the pressure should be reduced for cooling, and an interval of 12 hours is recommended between two consecutive blowdowns. 3.3 Improving the effect of pipe cleaning 3.3.1 To enhance the effectiveness of pipe cleaning, a certain amount of oxygen can be added to the basic steam cleaning method; this helps to remove rust and scale as well as promote the formation of a protective layer. 4. Installation of temporary facilities and technical requirements 4.1 Selection and installation of temporary control doors 4.1.1 Temporary control doors are one of the key components that affect the proper progress of the cleaning process; during cleaning, these doors are subjected to higher pressure differences and torques than under normal operating conditions. For the purging control valve, it is advisable to use an electric gate valve with a nominal pressure of not less than 6.4 MPa, a temperature tolerance of 450°C, and a diameter matching that of the main steam pipe (without manual control valves for temporary control). 4.1.2 Temporary control doors shall be installed horizontally, with an operating platform provided. 4.1.3 The temporary control door shall be operated remotely from the main control room. 4.2 Requirements for temporary connection pipes and steam exhaust pipes 4.2.1 The design pressure of the temporary connection pipes in front of the temporary control valve shall be no less than 9.8 MPa, the temperature shall be no less than 450°C, and the pipe diameter shall be the same as that of the main steam pipe ； The inner diameter of the temporary exhaust pipe should be greater than or equal to that of the pipe being cleaned, with a design pressure of 1.5 MPa and a temperature of 450°C. 4.2.2 For temporary exhaust pipes in the hot section, when it is difficult to select ones with the same diameter as the pipes in the hot section, temporary exhaust pipes with a total cross-sectional area that is 2/3 greater than that of the pipes in the hot section can be used. 4.2.3 When the manufacturer supplies automatic main steam valve protection equipment for high and medium pressure, the connection pipes and exhaust pipes shall lead out from the valve cover. 4.2.3.1 When the high-pressure door cover is located in front of the temporary control door, its strength shall be designed for a pressure of not less than 9.8 MPa and a temperature of 450°C ； When located behind a door: designed for a pressure of 4 MPa and a temperature of 450°C. The medium-pressure door cover can be designed for a pressure of 1.6 MPa and a temperature of 450°C. 4.2.3.2 When installing the high and medium pressure automatic main steam valve shutoff plates, attention must be paid to quality, and they must be verified by quality inspection personnel. 4.2.4 The temporary exhaust pipe should be installed horizontally, with the exhaust outlet tilted slightly upward to avoid buildings and equipment. 4.2.5 The supports and hangers for temporary connection pipes and exhaust pipes are properly arranged and firmly reinforced. 4.2.6 Steam flow measurement elements should not be installed during purging; when installing them after the purging is complete, attention must be paid to the manufacturing process, and it is strictly prohibited for iron slag and scale to fall into the pipes. For nozzle-type measuring elements, it is recommended to install them during the purging process and while the furnace is cooling down. 4.2.7 Blow out temporary connections; they should be inspected prior to installation, and constructed in accordance with the construction methods used for regular pipelines. 4.4 Installation of the target holder 4.4.1 The target holder is used to hold the target plates; attention should be paid to its structure and manufacturing process, as well as to its sufficient strength. Its design should be simple, it must provide good sealing, allow for easy operation, and facilitate the safe and convenient replacement of target plates. 4.4.2 The internal test target plate is installed in the purging connection pipe or exhaust pipe, as close as possible to the end of the purging pipe, on a straight section of pipe 4–6 m away from the elbow. 4.4.3 To properly test the quality of the blowing tube, the target plate should be polished and free from any visually visible defects. 4.5 Precautions after the purging is completed. 4.5.1 Upon the completion of the purging process and the restoration of the temporary system, reliable measures must be taken to prevent any secondary pollution. 5. Key points for implementing the blowing process 5.1 Basic conditions prior to blowing and cleaning 5.1.1 The installation of the boiler unit, the system equipment related to blowing and cleaning, as well as the temporary systems, along with the civil engineering work, have been essentially completed; in addition, the necessary on-site conditions are in place in accordance with clause 10.1.5 of the boiler section. 5.2 Key Points of Purging Process 5.2.1 Before the actual purging, 2–3 pre-purges at pressures lower than the selected purging pressure should be carried out to check the condition of the temporary equipment system used for purging and to become familiar with the control operations. Generally, the pre-purge pressures can be selected at 30%–40%, 50%–60%, and 70%–80% of the selected nozzle pressure, respectively. 5.2.2 During the initial pre-washing, a target plate can be installed and the target plate device can be activated in order to check the degree of dirtiness in the washing system as well as the performance of the target plate device. 5.2.3 During the purging process, a target plate can be used based on the exhaust conditions, steam quality, or to monitor the purging progress. 5.2.4 During the purging process, it is necessary to monitor the differential pressure of the superheater to ensure that, with the control valve fully open, this differential pressure is 1.4 times greater than the value under normal operating conditions. 5.2.5 The purging of other systems should generally be carried out after the purging of the main steam pipeline is completed, in order to prevent the pipelines that have already been purged from being contaminated again. 6. Safety and precautions for blowpipe operations 6.0.1 During blowdown, the steam flow from the exhaust outlet must be directed away from buildings and equipment. A warning zone should be established, and a dedicated person should be assigned to monitor it. 6.02 During cleaning operations, public notices should be issued to inform the public, and the scope of construction work should be adjusted; high-altitude work should be avoided, and cleaning at midnight should be prevented as much as possible. 6.0.3 Implement reliable fire prevention measures. Ensure that sufficient fire-fighting equipment is available, and assign dedicated personnel to inspect it; any issues found should be addressed promptly. 6.0.4 Strengthen the stable operation of the steam system to avoid significant pressure fluctuations. 6.0.5 Reliable safety measures are in place when replacing the target plate. 6.0.6 Ensure adequate drainage of warm pipes to prevent water impact. 6.0.7 Strictly implement the operation ticket, work ticket systems, and routine inspection systems; pay attention to the inspection and maintenance of operating equipment, and conduct inspections of pipeline supports, hangers, and isolation systems. 6.0.8 Formulate anti-accident measures. Blowing tube operation and accident handling shall be carried out in accordance with the operating procedures, blowing tube measures, and accident handling measures. 6.0.9 After the purging is completed, anti-corrosion and anti-freezing measures should be determined in conjunction with relevant personnel.

Purge and Targeting Operation Card 100: Purge – 110: Preparation Work I ( ) – Confirm that the main steam flow orifice plate has been removed; I ( ) – Confirm that the main steam temperature gauge tube has been removed; I ( ) – Confirm that the desuperheater has been removed; I ( ) – Confirm that the temporary pipelines for purging are in place; I ( ) – Confirm that the target used for purging is ready; I ( ) – Confirm that the electric valve used for targeting operates properly; I ( ) – Confirm that the electrical contact level gauge gives accurate readings; I ( ) – Confirm that the local level gauge is clear and accurate; I ( ) – Confirm that the main steam pressure signal is accurate; I ( ) – Confirm that the saturated steam pressure signal is accurate. P – Switch to the main steam line for purging process. 120: Purging and Targeting I ( ) – Confirm that the acid cleaning of the external saturated steam line is complete. M – Contact the maintenance team to restore the external saturated steam flow orifice plate; M – Contact the maintenance team to restore the temperature gauge tube. P – Introduce approximately 15 t/h of external saturated steam into Furnace C. P – Close the superheated steam vent valve to 3 positions. Note: The vent valve must not be closed completely; it is necessary to ensure that steam continues to flow through the superheater to prevent it from burning out. I – Adjust and control the combustion properly. I ( ) – Confirm that the superheated steam pressure reaches around 3.0 MPa. I – Activate the electric valve for purging to begin the purging process. I – Stop purging when the superheated steam pressure drops to 1.5 MPa. Note: After purging, check the condition of the pipeline supports; if any problems are found, stop purging. I ( ) – Confirm that the main steam line has been purged 5 times. M – Contact the maintenance team to install the target. I – Perform targeting. I – Check the target. I ( ) – Confirm that the main steam line has been properly purged. I – Stop using the main steam line for testing purposes. IP – Shut down the waste heat boiler. M – Contact the construction team to remove the temporary facilities used for testing. M – Contact the construction team to restore the temperature regulator on the main steam line. M – Contact the construction team to restore the flow meter on the main steam line. I – Stop the furnace and proceed with cooling. M – Contact the team to conduct a thorough inspection of the furnace. Final state: The boiler has been purged and tested; the pipes are cooling naturally

Before putting steam pipelines in use in steam-driven units such as turbines, blasting tests must be conducted to check the cleanliness of the pipelines, thereby preventing particle impurities such as iron filings from entering the equipment and damaging the rotor. For the steam pipes leading to the turbine, the target plates used for shooting should be made of aluminum sheets with a thickness of 5 mm, a width of at least 8% of the inner diameter of the exhaust pipe, and a length slightly greater than the inner diameter of the pipe ； Size of marks on the target sheet: below φ0.6 mm, with a standard particle count of 1 per/cm2. This post was last edited by maysee on 2008-1-31 16:19.]

I am extremely grateful to the original poster and the friends who provided answers; thank you all. I’m not the original poster, but I really needed this information. Thank you very much.

I am extremely grateful to the original poster and the friends who provided answers; thank you all. I’m not the original poster, but I really needed this information. Thank you very much.