What are the appropriate steam pressure and flow rate requirements when purging a 3.8 MPa steam pipeline?

Steam pipeline targeting plan I. Purpose of targeting: To remove various impurities such as rust and slag from the pipes, and to protect the blades of the steam turbine. II. Requirements for target shooting 1. Form a purging team for target shooting ； 2. To save shooting time and steam consumption, the pipelines were previously chemically cleaned (acid cleaning and passivation) ； 3. The target pipeline has been purged and made leak-free ； 4. All instrument components on the pipeline prior to shooting (such as flow meters, orifice plates, venturi tubes), control valves, etc., have been removed or protected by appropriate measures ； 5. Install blind plates on equipment and pipelines that pose a safety risk, label them and number them, with a designated person responsible for keeping records ； 6. Temporary pipes led to a safe location must comply with the following requirements: (1) The outlet of the exhaust pipe should be inclined upward (about 30° is appropriate), leading to an open area ； (2) The exhaust pipe shall have secure support to withstand the reaction force of the exhaust gas ； (3) The inner diameter of the exhaust pipe should be equal to or greater than that of the pipe being cleaned, and its length should be as short as possible to reduce resistance ； (4) The butt welding requirements for the exhaust pipe are the same as those for regular welds, and a silencing device shall be installed. 7. The steam used for purging and target shooting is sourced from the medium-pressure steam network (3.5 MPa, 410°C), with coordination handled uniformly by the company’s dispatch team ； 8. Before steam purging, the pipes should be pre-heated and water should be drained promptly; the thermal displacement of the pipes should also be checked ； 9. The purging process should be carried out in more than two stages, with each stage lasting approximately 20–30 minutes. A interval of 12 hours should be allowed between consecutive purging sessions to allow the pipeline to cool down; once the second stage begins, target plates can be installed continuously for testing purposes ； III. Target range: 1. 3.5 MPa superheated system: To the two busbars of the 3.5 MPa system in the critical zone; 2. 3.5 MPa saturated system: From the saturated steam outlet of the boiler drum to the drain point at the superheater outlet. During the first startup, spontaneous steam is used for pressure reduction and purging; after that, the boiler is shut down and the drum is drained to release pressure. The low-point valve or flange at the superheater outlet drain is then opened to inspect and remove any heavy impurities that cannot be removed through steam purging, after which normal operation can resume. IV. Estimation of the steam volume for testing purposes: Rated load of the 3.5 MPa superheated steam system and steam volume for testing purposes (unit: t/h): For the external delivery system, the diameter of the outlet pipe for testing purposes is DN400; the steam volume for testing purposes is greater than 51 t/h. The steam volume for testing purposes is estimated to be at least 60% of this value (see the table above). V. Targeting standards: The cleaning effect is checked using a target plate installed inside the exhaust pipe (or at the exhaust outlet). The target plate can be made of aluminum, with a width of approximately 8% of the inner diameter of the exhaust pipe, and a length that spans the entire inner diameter of the pipe ； Under the condition of ensuring the aforementioned scouring force, after two consecutive replacements and inspections of the target plate, the particle size of the impact marks on the plate shall not exceed 0.8 mm, and the number of marks shall not be more than 8; in such cases, the cleaning process is considered successful.

This post was last edited by mby_1983 on 2014-11-4 21:51. IV. Estimation of the steam volume for testing purposes: Rated load and steam volume for testing in a 3.5MPa superheated steam system (unit: t/h): External delivery system, diameter of the outlet pipe for testing purposes, steam volume for testing – 84.6, DN400; steam volume >51. This is quite similar to our operating conditions. For 3.8MPa superheated steam with an inner pipe diameter of 300, can we calculate the steam volume required for testing? One boiler meets the requirement of 75 t/h; there is also a user with a demand of 65 t/h, which leaves 10 t/h – is that not enough?