General fabrication requirements for our transmission tower

First and foremost，both parties must discuss all drawings and confirm all shop drawings, technical specification, and which standard to conform.Before mass production, we must received all signed approved shop drawings and technical documents from our client.

Our Fabrication shall be in strict accordance with detail Drawings prepared by the Contractor and approved by the Engineer.            Fabrication shall begin after the approval of the shop assembly and tests.

Shearing

1. Shearing and cutting shall be performed carefully and all portions of the work which will be exposed to view after completion shall be finished neatly. Manually guided cutting torches shall not be used.

2. All material over 13 (or 12) mm thick shall be cold sawn or machine flame cut.

3. Cropping or shearing shall be allowed for material thickness of 13 mm or less.

4. Flame cutting of high yield steel shall be preceded by a slight preheat operation by passing the cutting flame over the part to be cut.

5. All flame-cut edges shall be ground clean.

Bending

1. Bending shall be carried out in such a manner as to avoid indentation and surface damage. 

2. All bending over 5 degree celsius, or high yield steel, shall be performed while the material is hot.

Welding

1. No welding shall be done unless prior approval has been obtained from the Engineer.

2. Welding shall not be allowed at tower attachment points for conductor, shieldwire, insulators or associated assemblies or brackets.

Sub-punching

1. All holes in structural steel less than 10 mm thickness may be punched to full size unless otherwise noted on the approved Drawings. 

2. Holes shown on the Drawings as drilled holes and all holes in structural steel 10 mm or more in thickness and tension members of crossarms shall be drilled or sub-punched and reamed.

3. All holes shall be clean cut and without torn or ragged edges.            4. All burrs resulting from reaming or drilling shall be removed.            5. All holes shall be cylindrical and perpendicular to the member.

6. Where necessary to avoid distortion of the holes, holes close to the points of bends shall be made after bending.

Punching

1. For punching to full size, the diameter of the punch shall be 1.0 mm larger than the nominal diameter of the bolt, and the diameter of the die shall not be more than 1.5mm larger than the diameter of the punch. 

2. For sub-punching, the diameter of the punch shall be 4 mm smaller than the nominal diameter of the bolt, and the diameter of the die shall be not more than 2 mm larger than the diameter of the punch. Sub-punching for reamed work shall be such that after reaming no punch surface shall appear in the periphery of the hole.

Hole Size

Where holes are reamed or drilled, the diameter of the finished hole shall be not greater than the nominal diameter of the bolt plus 1.0 mm.

Accuracy

1. All holes shall be spaced accurately in accordance with the Drawings and shall be located on the gauge lines.

2. The maximum allowable variation in hole spacing from that indicated on the Drawings for all bolt holes shall be 0.8 mm.

Fabrication Tolerances

A specification for tolerances shall be submitted for approval by the Engineer prior to commencement of fabrication.

Bolt List

A complete list of bolts showing their lengths and the members, which they are to connect shall be given on the erection diagrams.

Locking Devices

Locking devices for tower bolts will not be required, but point punching shall be performed.

Anti-theft Fasteners

Appropriate anti-theft fasteners for example Huck-bolting shall be applied on all the towers up to the level of anti-climbing devices, to prevent theft of tower members.

Piece Marks

All pieces shall be stamped before galvanizing with the piece marks shown on the erection Drawings, with the marking not less than 20 mm high placed in the same relative location on all pieces.   The marking shall be plainly visible after galvanizing.

Galvanizing

1. All material shall be hot-dip galvanized after fabrication in accordance with the latest revision of GB/T 13912-2002 or ASTM Specification A 123.

2. Material that has been rejected because of bare spots or other coating defects shall either be stripped and re-galvanized, or the uncoated areas shall be recoated by an approved method.

3. All plates and shapes which have been warped by the galvanizing process shall be straightened by being re-rolled or pressed. The material shall not be hammered or otherwise straightened in a manner that will injure the protective coating.

4. Approval shall be secured from the Engineer if galvanizing is done outside of the Contractor's plant.

5. All galvanized steelwork shall be protected against white storage stain by using an approved dichromate solution treatment immediately following galvanizing.