For regular steam purging, how are the parameters of the purge nozzle determined?
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For ordinary steam pipes, are pipe cleaning parameters also required during purging? This includes selecting the pressure and temperature of the purge steam, checking the specific volume of the steam, calculating the blowpipe coefficient K value, and thereby determining the amount of steam required After checking, the calculation of the blowpipe coefficient is mainly used for pipeline purging in thermoelectric boiler units ； GB50235-97 only states that \"steam pipes should be purged with high-flow steam, at a flow rate of not less than 30 m/s\" when discussing steam purging, and does not mention the purge coefficient. So, which standard is followed for the purging of ordinary steam pipelines? I calculated it separately, and the results obtained using these two methods differ greatly. Another question: during steam purging, what are the appropriate pressure and temperature levels for the steam in order to ensure effective purging?
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The flow rate for pipeline purging is primarily determined by the diameter of the pipeline to be purged and the flow volume. If the gas source connected is the main pipeline in the plant, a flow rate of 2 t/h is sufficient for pipelines with diameters ranging from DN65 to DN150; this value can be calculated using the tables for outdoor high-pressure steam pipelines.
Thank you! I first searched on the forum, but it still didn’t seem very clear to me. The main issue is that the calculation results based on electrical standards and national standards differ significantly; it’s not clear now which standard should be followed Secondly, I would like to know how this is handled in actual engineering practice – are there any established methods? Should we still operate based on the actual situation?
Small pipes should be straightforward to handle, but my main steam pipes are as large as DN300 or more; a low flow rate would likely result in poor performance. “Where can I find the “Outdoor high-pressure steam pipe diameter calculation table”? Can it be found or calculated in this table? Thank you!
Piping steam purging can be carried out in accordance with the \"Code for Construction and Acceptance of Industrial Metal Piping Projects\" GB 50325-97. 8. Purging and cleaning of pipelines 8.1.1 After the pipelines pass the pressure test, the project owner shall be responsible for organizing the purging or cleaning (referred to as purging and cleaning) process, and a plan for this purpose shall be prepared prior to carrying out such operations. 8.1.2 The purging method shall be determined based on the usage requirements of the pipeline, the working medium, and the degree of dirtiness on the inner surface of the pipeline. For liquid or gas pipelines with a nominal diameter of 600 mm or more, manual cleaning is recommended; for liquid pipelines with a nominal diameter of less than 600 mm, water flushing is advisable ； Gas pipelines with a nominal diameter of less than 600 mm should be purged with air ； Steam pipes should be purged with steam ； Non-thermodynamic pipelines must not be purged with steam. For pipes with special requirements, the corresponding cleaning methods specified in the design documents shall be used. 8.1.3 Equipment and pipelines that are not allowed to be purged shall be isolated from the purging system. 8.1.4 Before pipeline purging, orifice plates, flanged control valves, important valves, throttle valves, safety valves, instruments, etc., should not be installed. For the welded valves and instruments mentioned above, protective measures such as using bypass circuits or removing the valve heads and seats and covering them with protective sleeves should be taken. 8.1.5 The purging sequence shall be in the order of main pipes, branch pipes, and drainage pipes; the dirt removed during purging must not enter the pipes that have already been deemed satisfactory. 8.1.6 Before purging, the stability of pipe supports and hangers should be checked, and reinforcement should be carried out if necessary. 8.1.7 The dirty liquid discharged from cleaning must not contaminate the environment; discharging it indiscriminately is strictly prohibited. 8.1.8 A no-entry zone should be established during purging. 8.1.9 During steam purging, no flammable materials shall be placed on or near the pipes. 8.1.10 After the pipeline has been successfully purged and restored to its normal state, no other operations that could affect the cleanliness inside the pipeline shall be carried out. 8.1.11 When resetting the pipes, the construction unit shall, together with the project owner, conduct inspections, and fill out the “Piping System Purging and Cleaning Records” as well as the “Hidden Works (Sealing) Records” in the format specified in Articles A.0.9 and A.0.4 of Appendix A to these specifications. 8.2 Water Flushing 8.2.1 Clean water should be used for flushing pipes; when flushing austenitic stainless steel pipes, the chloride content in the water must not exceed 25×10-6 (25PPm). 8.2.2 During flushing, the maximum flow rate should be used, with the flow velocity not being less than 1.5 m/S. 8.2.3 The discharged water shall be introduced into a reliable drainage well or ditch, and the cross-sectional area of the 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. 8.2.4 All drainage branches of the pipes shall be flushed. 8.2.5 Water flushing shall be carried out continuously, and it is considered successful when the color and transparency of the water at the outlet are visually consistent with those of the water at the inlet. 8.2.6 When the pipeline is not put into operation temporarily after passing the water flushing test, the water should be drained completely and it should be dried promptly. 8.3 Air Purging 8.3.1 Air purging should be carried out using the large compressors of the production facility, or by utilizing the large storage tanks in the facility to hold air for intermittent purging. The purging pressure must not exceed the design pressure of the vessels and pipes, and the flow rate should be no less than 20 m/S. 8.3.2 When purging oil-free pipelines, the gas must be free of oil. 8.3.3 During the air purging process, once it is visually confirmed that no smoke or dust is present in the exhaust gas, a wooden target covered with white cloth or painted white should be placed at the exhaust outlet for inspection. If there is no rust, dust, moisture, or other debris on the target within 5 minutes, it is considered acceptable. 8.4 Steam Purging 8.4.1 The temporary pipes installed for steam purging shall be installed in accordance with the technical requirements of steam pipes, and the installation quality shall meet the provisions of these specifications. 8.4.2 Steam pipes shall be purged with high-flow steam, at a flow rate of not less than 30 m/s. 8.4.3 Before steam purging, the pipes should be pre-heated, water should be drained promptly, and the thermal displacement of the pipes should be checked. 8.4.4 Steam purging shall be carried out in cycles in the order of heating—cooling—reheating. During purging, it is advisable to purge one at a time in a rotating manner. 8.4.5 For steam pipes leading to the turbine or as specified in the design documents, the test target plates shall be inspected after steam purging. When the design documents do not specify, its quality shall meet the requirements specified in Table 8.4.5. Purging quality standards Table 8.4.5 Item Quality standard Size of marks on the target Plate: ≤0.6 mm Depth of marks: <0.5 mm Number of particles: 1 per cm2 Time: 15 min (both attempts must be successful) Note: The target should be made of an aluminum plate 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. 8.4.6 In addition to the inspection of steam pipes specified in Article 8.4.5 of these specifications, steam pipes may also be inspected using planed wooden boards; they are considered satisfactory if no rust or dirt is present on the boards after purging.
The main purpose of pipeline steam purging is to remove impurities such as weld slag and rust from within the pipes; therefore, there is no need to determine the specific volume of steam, calculate the purging coefficient K, or compute the amount of steam required. The steam pressure for purging need only not exceed the design operating pressure of the pipeline. If it is necessary to know the amount of steam required for purging, it is advisable to install a steam metering system temporarily.
Regarding the claim by the original poster that there is a large difference when calculating according to national standards and industry standards, it is generally appropriate to follow the industry standards, as national standards are relatively less stringent than industry standards. For example, our power station boilers must be designed in accordance with the regulations of the power industry; that is, the most stringent standards are used for calculations. As long as a certain standard applies to a particular situation, that standard should be followed strictly. In the past, when dealing in steel pipe exports, we used the American standards API and ASTM for delivery, and wherever there was overlap, the stricter of those standards was applied – the same principle applies here.