【Acceptance-related】Issues regarding steam purging of steel slag in pipelines
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Our company has recently built a new factory complex in Qidong, dedicated to the production of synthetic heat transfer oils. The main equipment includes a condensation system (primarily made of glass-lined pipes) and a distillation system (using carbon steel pipes). The equipment has now been installed, and piping work has begun. Then the veteran engineer told me that I need to develop a plan for steam purging (there will be steel slag inside during pipe welding, so it must be cleaned out). Since I had never done this before, I went online to look for information. I found that it was said that specialized equipment and construction teams were required for such tasks. Moreover, most examples of cleaning processes mentioned online related to steam pipelines; I didn’t see anyone talk about cleaning ordinary material pipelines. When I showed this to the expert, he was also confused. Therefore, I have come here specifically to ask fellow sailors: how is the steel slag left behind after welding inside pipes generally removed? I would like to thank everyone here first~ PS: The park provides a steam pipeline, so using steam for purging was an idea that came to mind from the start; of course, this also limited our thinking. PS2: Using water to flush it seems unlikely to work, as some of the pipelines are quite long and the steel slag is quite heavy. PSP: Although there is an air compressor available, its power is low, so it probably won’t work either
As a makeshift solution, disassemble the flange connection and insert a long enough wire; tie a cloth ball to one end of the wire – the size of the cloth ball should correspond to the diameter of the pipe. Pull the wire out from the other end, and this will help remove most of the slag inside. For the rest, using steam is an effective method; it’s fast, and it’s better to follow this approach for each section during installation. If the pipe is long and lacks flanges, then steam cleaning is used directly; this process is rather slow. I have used steam to clean high-pressure steam pipes in boilers. During installation, no attention was paid to this aspect, and steam cleaning was carried out directly. It took several days to complete the cleaning process, with the steam pressure increasing from 10 kilograms to 35 kilograms. In total, around 100 pieces of debris were removed using this method, and it was a very time-consuming process. It seems you’ll most likely have to do this! There’s too much waste.
During pipeline prefabrication, sectional purging should be carried out first, followed by sealing the pipe ends, and finally, steam purging of the system.
Just joining in the fun; no, definitely don’t laugh. If most of the pipelines can be resolved by passing the ball through them, can we ignore the remaining part?
Thank you for your reply. I was wondering, can this be done for non-pressure pipelines as well? Using wire to tie cloth balls and things like that probably won’t work – there are too many bends……
Only steam purging can be used; other methods simply cannot clean them thoroughly. If higher standards are required, blasting is necessary. The pipelines in front of the turbines at our facility took two days of blasting purging before they met the requirements.
GB 50235 \"Code for Construction of Industrial Metal Piping Projects\" 9 Purging and Cleaning of Piping 9.1 General Provisions 9.1.1 After passing the pressure test, the piping shall be purged and cleaned. A pipeline purging and cleaning plan should also be prepared. 9.1.2 The methods for purging and cleaning pipelines shall be determined based on the usage requirements of the pipelines, the working medium, the system layout, the site conditions, and the degree of dirt on the inner surface of the pipelines. These methods shall comply with the following regulations: For liquid or gas pipelines with a nominal diameter of 600 mm or greater, manual cleaning is preferred. Scan. 2 Liquid pipes with a nominal size of less than 600 mm should preferably be flushed with water. 3 For gas pipelines with a nominal size of less than 600 mm, compressed air purging is recommended. 4 Steam pipes should be purged with steam; non-thermal pipes shall not be purged with steam. 5 For pipes with special requirements, the corresponding purging and cleaning methods specified in the design documents shall be used. 6 High-pressure water flushing, air blasting cleaning, or other cleaning and purging methods can be employed as needed. 9.1.3 Before pipeline purging and cleaning, the stability of the pipeline supports and hangers should be carefully checked, and any sections that appear problematic should be reinforced. 9.1.4 Equipment and pipelines that are not allowed to be purged or cleaned should be isolated. 9.1.5 Before pipeline purging and cleaning, the instrumentation, orifice plates, nozzles, filters, throttle valves, control valves, solenoid valves, safety valves, check valves (or check valve elements) and other components within the system should be temporarily removed and replaced with simulants or temporary short pipes; they should be reinstalled once the pipeline purging is completed successfully. For the aforementioned valves, instruments, and other components that are connected by welding, protective measures such as using a bypass flow or removing the valve stem and seat and covering them with protective sleeves should be taken before performing purging and cleaning. • 55 • 9.1.6 The sequence of purging and cleaning should be carried out in the order of main pipes, branch pipes, and drainage pipes. The dirt washed out must not enter the pipes that have been properly purged and cleaned. 9.1.7 The temporary water supply, gas supply pipes, and drainage pipes installed for pipeline purging and cleaning must be thoroughly purged and cleaned before being put into use. 9.1.8 When purging and cleaning pipelines, exclusion zones and warning lines should be established, along with warning signs. 9.1.9 When using air blasting or steam purging, measures such as installing silencers at the discharge outlets should be taken. 9.1.10 The treatment and discharge of chemical cleaning waste liquids, degreasing residues, and other waste liquids and wastewater must comply with the provisions of **current relevant standards; such substances shall not be discharged indiscriminately. 9.1.11 After the pipeline has been purged and cleaned successfully, no other operations that could affect the cleanliness inside the pipeline shall be carried out, except for the specified inspection and restoration tasks. 9.1.12 During chemical cleaning and degreasing operations, operators must wear specialized protective clothing as required, and they should also use protective equipment such as safety glasses and gas masks, depending on the degree of harm that various cleaning agents can pose to the human body. 9.1.13 After the pipeline purging and cleaning are completed successfully, the construction unit shall, together with the project owner or the supervision unit, conduct an inspection to confirm this, and fill out the \"Pipeline System Purging and Cleaning Inspection Record\" as well as the \"Pipeline Concealed Works (Sealing) Record\"; the format of these documents should comply with the requirements specified in Tables A.0.17 and A.0.7 of these specifications.
9.2 Water flushing 9.2.1 Clean water should be used for pipeline flushing. When flushing stainless steel, brass, and nickel alloy pipes, the chloride ion concentration in the water must not exceed 25 X 10-6 (25 ppm). 9.2.2 The flow velocity for water flushing of the pipes shall not be less than 105 m/s. The flushing pressure shall not exceed the design pressure of the pipes. 9.2.3 The cross-sectional area of the flushing discharge pipe shall not be less than 60% of the cross-sectional area of the pipe being flushed. Negative pressure must not be created during drainage. 9.2.4 Pipe water flushing shall be carried out continuously; when not specified in the design, the color and transparency of the water at the outlet shall be consistent with those measured daily at the inlet. • 56 • 9.2.5 For pipes with severe rust and contamination, when conventional cleaning methods are insufficient, the pipes can be flushed with high-pressure water in sections. 9.2.6 After the pipeline flushing is completed successfully, the water accumulated inside the pipeline should be drained promptly, and it should also be dried as soon as possible.
9.3 Air Purging 9.3.1 Air purging should be carried out intermittently using the large air compressors or large air storage tanks available in the factory’s production facilities. The purging pressure shall not exceed the design pressure of the system’s containers and pipelines, and the purging flow rate should be no less than 20 m/s. 9.3.2 When purging oil-free pipelines, oil-free compressed air or other oil-free gases should be used for purging. 9.3.3 During air purging, a wooden target board covered with a white cloth or painted white should be placed at the exhaust outlet for inspection; after 5 minutes of purging, there should be no rust, dust, moisture, or other debris on the target board. 9.3.4 When the volume of the system to be purged is large, the pipelines are long and have large diameters, and it is not suitable to use water for flushing, the \"air blasting method\" can be employed for purging. During blasting purging, the pressure of the gas injected into the system shall not exceed 0.5 MPa, and appropriate safety measures shall be taken.
9.4 Steam Line Purging 9.4.1 Before purging the steam pipes, the insulation work for the pipeline system must have been completed. 9.4.2 Temporary pipes installed for steam purging shall be constructed in accordance with the technical requirements for the installation of regular steam pipes, and their installation quality shall meet the relevant provisions of this specification. It should be used for purging the main steam pipeline only after the temporary pipeline has been thoroughly purged. 9.4.3 Steam pipes shall be purged with high-flow steam, at a flow rate of not less than 30 m/s. 9.4.4 Before steam purging, the pipes should be warmed up first, and water should be drained promptly. When warming the pipes, their thermal displacement should be checked, and any abnormalities should be addressed promptly. 9.4.5 During steam purging, no flammable, explosive materials or other debris shall be placed on or near the pipes. 9.4.6 Steam purging shall be carried out in a cycle of heating, cooling, and reheating. During purging, it is advisable to purge one pipe at a time or in a rotating manner. 9.4.7 The exhaust pipe shall be installed outdoors, with its outlet inclined upward. The diameter of the exhaust pipe should not be smaller than the diameter of the pipe being purged. 9.4.8 For steam pipes leading to the turbine or as specified in the design documents, the purging target plates shall be inspected after steam purging. The target plates for final acceptance shall be properly labeled and stored carefully.
I read that 50235 earlier in the morning… It’s really frustrating. I don’t care anymore; I’ll just prepare a plan based on these standards. Let the old mage go ahead and prepare a report on what equipment needs to be purchased, hahaha……