Nauru Bolt heating bar and DC cabinet

1.Series of the bolt heating bar and DC cabinet

Because different types and sizes of bolts are used in the steam turbine, so the bolt heating bars are provided in according series, which include DJ-15, ZJ-15, DJ-16, ZJ-16, DJ-17, ZJ-17, DJ-18, DJ-20, ZJ-20, DJ-22, ZJ-22, DJ-24, DJ-27, DJ-36  and so on.

2. Technical requires of the bolt heating bar (DJ22 series as example) and DC cabinet

2.1. The bolt heating bar of steam turbine and its DC cabinet should meet the following requirements:

2.1.1. Raw materials for bolt heating bar shall meet the following requirements:

① The composition of insulating material magnesium oxide shall comply with HG3-1294-80 "Magnesium Oxide";

② Magnesium oxide must be dried before use;

③ The electric heating material used for the electric heater is 0Cr27A17Mo2 high resistance electric heating alloy wire, and its working temperature is 400 °C. the technical requirements are in accordance with GB1234 high resistance electric heating alloy;

④ The protective sleeve material of electric heater is 1Cr18Ni9Ti heat-resistant stainless steel pipe. The technical requirements shall be in accordance with YB804 stainless and acid resistant steel seamless steel pipe. The use of other materials shall be agreed between the manufacturer and the user;

⑤ After deburring the inside of the protective sleeve for electric heater, clean it with gasoline or kerosene and blow dry it before use.

2.1.2. The finished product of bolt heating bar shall meet the following requirements:

① The rated working voltage of electric heater is 220 ± 20V. DC 100V, LV 50V;

② If the insertion length of the electric heater is within 1m, the straightness of the center line shall not be greater than 0.3mm； If the insertion length is 1-2m, the straightness of the center line shall not be greater than 0.4mm；

③ The diameter deviation of the inserted part is -0.20mm / - 0.50mm;

④ The length deviation of the insertion part is ± 5mm, the heating length deviation is ± 5mm, and the length of the cold end at the bottom is 25-30mm;

⑤ The electric heater shall be heated evenly during use, and local overheating is not allowed.

2.2. During the life test of electric heater, each heating time is 10-20min. The electric heater is under intermittent heating.

The total clearance between the bolt center hole and the outer diameter of the electric heater shall be 0.8-1.3mm, and the cumulative service life shall not be less than 50h.

2.3. The connection between alloy resistance wire and outgoing line shall be firm and reliable without looseness. The enclosure must be well grounded.

2.4. After the steel sleeve of electric heater is cold drawn and shrunk, the surface shall be inspected by dye flaw detection or more than 5 times magnifying glass, and there shall be no cracks and other defects. When shrinking the pipe, it shall be formed in one direction.

2.5. The sealing of the cold end of the electric heater shall be tight to prevent moisture from entering and damaging the insulation.

2.6. After the electric heater is manufactured, after one and a half months, the insulation resistance shall be measured with a 500V megger at room temperature (conducted at the manufacturer or user) and shall not be less than 50mΩ.

3. Parameters of the bolt heating bar (DJ22 series as example)

Remark for the table:

1. The electric heater parameters listed in this table are applicable to bolts with center hole diameter d = 22.6 ± 0.2mm. The electric heater that does not meet the center hole diameter and specification parameters listed in this table shall be negotiated between the user and the manufacturer.

2. The surface power density of the electric heater listed in this table is 8-11W / cm².