5.2　Backing Ring

5.2.1　The split backing ring shall be assembled on site according to the requirement of the design technical document or the written technical instruction of the supplier's field representative.In case of no above-mentioned requirement or instruction，the requirements of Articles 5.2.2-5.2.5 of the code shall be complied with.

5.2.2　The backing ring shall be assembled on the platform which shall be firm and stable and can bear the equipment weight and the compact happening during assembly.The assembled backing ring should be finally adjusted and inspected after the platform has completely settled and remains stable.

5.2.3　The assembly of butt-welded backing ring shall comply with the following requirements:

1　The coaxiality of two trunnions shall be adjusted and not larger than 0.7mm prior to welding.The horizontal coaxiality shall be checked with a precise level，and the vertical coaxiality shall be checked with a micrometer and suspension wire.Some related dimensions shall also be checked based on the design drawings.

2　After the butt-welded backing ring is checked as qualified，the butt joints should be rigidly fixed with a positioning board，and the positioning boards at the same butt joints shall be also butt welded.During welding，the coaxiality changes shall be monitored.

3　Prior to butt welding，the corresponding welding procedure qualification（WPQ）shall be carried out and the operation instruction for welding shall be prepared based on the WPQ report.The welding shall be carried out in strict accordance with the instruction.

4　The welds of two butt joints shall be welded symmetrically at the same time.The welds inside and outside of left and right vertical plates as well as upper and lower cover plates（box structure）shall be welded in reasonable sequence which shall be properly adjusted according to the monitoring data of deformation timely.

5　During welding，the welding deformation shall be tracked and monitored according to Item 1 of this Article and the following measures:one micrometer（eight in total）shall be respectively equipped at 0°（for vertical change）and 90°（for horizontal change）of end and root of every long or short trunnion to measure the coaxiality change of trunnion at any time.

6　The appearance quality of welding seam shall conform to related requirements of current national standard Code for Installation Acceptance of Steel-making Mechanical Equipment GB 50403.

7　The internal quality of welding seam shall conform to related requirements of current national standard Code for Installation Acceptance of Steel-making Mechanical Equipment GB 50403.

8　The postweld heat treatment of paired welding seam shall conform to related requirements of current national standard Code for Installation Acceptance of Steel-making Mechanical Equipment GB 50403.

9　The coaxiality of two trunnions shall be inspected with the allowable deviation of 1.5mm.

5.2.4　The assembly of backing rings connected with flanges shall comply with the following requirements:

1　The burr，paint and dirt shall be removed from the mesh face，key and keyway of flanges which shall be cleaned up after then.

2　The backing rings shall be paired，the coaxiality of two trunnions shall be checked，and some related dimensions shall be checked according to the design drawing.

3　The flange connecting bolts shall be assembled，and fastened symmetrically，crosswise，evenly and orderly.The tightening force shall meet the requirement of the design technical document and the coaxiality of two trunnions shall be monitored during tightening.

4　The shaped key shall be assembled and positioned according to the requirement of the design technical document.

5　Clearances between the mesh faces of flanges shall be inspected and not larger than 0.05mm.6　The coaxiality of two trunnions shall be inspected with the allowable deviation of 1.5mm.

5.2.5　The backing-ring water cooling system shall be subject to hydrostatic test and flushing test.These tests shall conform to the requirement of the design technical document.In case of no related requirement in the document，the tests shall comply with the following requirements:

1　The test pressure shall be 1.25 times of working pressure.Booster the pressure up to the test pressure and hold for 10min，and then lower it up to the working pressure and hold for 30min.The test is qualified if there is no leakage or pressure fall.

2　For flushing test，the water shall be able to flow in and out smoothly and freely for at least 24h，without any leakage.