Bolt Heating Rod
(I) The steam turbine bolt electric heater shall meet the following requirements:1. The raw materials used for the electric heater shall meet the following requirements:
① The composition of the insulating material magnesium oxide shall comply with the provisions of HG3-1294-80 "Magnesium Oxide";
② Magnesium oxide must be dried before use;
③ The heating material used for the electric heater is 0Cr27A17Mo2 high-resistance electric heating alloy wire, with a working temperature of 400°C, and technical requirements according to GB1234 "High Resistance Electric Heating Alloy";
④ The protective tube material of the electric heater is 1Cr18Ni9Ti heat-resistant stainless steel tube. Its technical requirements shall comply with YB804 "Stainless and Acid-Resistant Seamless Steel Tubes". Use of other materials shall be agreed upon between the manufacturer and the user;
⑤ The inside of the protective tube used for the electric heater shall be deburred, then cleaned with gasoline or kerosene, and dried before use.
2. The finished electric heater shall meet the following requirements:
① The rated working voltage of the electric heater is 220±20V. DC 100V, low voltage 50V;
② For insertion length within 1m, the straightness of the centerline shall not exceed φ0.3mm; for insertion length between 1-2m, the straightness of the centerline shall not exceed φ0.4mm;
③ The diameter deviation of the insertion part is -0.20mm/-0.50mm;
④ The length deviation of the insertion part is ±5mm, the heating length deviation is ±5mm, and the cold end length at the bottom is 25-30mm;
⑤ The electric heater shall have uniform heating during use, and local overheating is not allowed.
(II) When performing life tests on the electric heater, each heating time is 10-20 minutes. Under intermittent heating conditions, with the total gap between the bolt center hole and the outer diameter of the electric heater being 0.8-1.3mm, the cumulative service life shall not be less than 50 hours.
(III) The connection between the alloy resistance wire and the lead-out wire shall be firm and reliable, without looseness. The outer shell must be properly grounded.
(IV) After the steel tube of the electric heater is cold-drawn and reduced, its surface shall be inspected by dye penetrant testing or with a magnifying glass of 5x or more, and there shall be no defects such as cracks. The tube reduction shall be formed in one direction.
(V) The sealing at the cold end of the electric heater shall be tight to prevent moisture from entering and damaging the insulation.
(VI) After the electric heater is manufactured, after one and a half months, its insulation resistance shall be measured at room temperature with a 500V megohmmeter (can be performed at the manufacturer or user site) and shall not be less than 50 MΩ.
Test Methods and Acceptance Rules
After assembly, each electric heater shall have its insulation resistance measured at room temperature with a 500V megohmmeter, which shall not be less than 50 MΩ. It shall also withstand a 1500V withstand voltage test for 1 minute without breakdown or flashover. Then, in air, under rated working voltage, it shall be powered and heated for 2-3 minutes without overheating, and the insulation resistance shall not be less than 0.5 MΩ, with leakage current not exceeding 0.5mA per kilowatt. Its power shall be checked to see if it meets the order requirements (deviation ±5%). After the test, check whether all parts of the electric heater are intact.Each electric heater shall be inspected and approved by the manufacturer's quality inspection department, and accompanied by a certificate of conformity before shipment.
