Attaching of cathodic protection cable by pin brazing and aluminothermic weld (Cadweld)
Brazing is the process of joining metal by heating the base metal to a temperature above 800°F and adding a
nonferrous filler metal that melts below the base metal.
CADWELD is an exothermic welding, in which the filler metal is melt down by the exothermic oxidization of aluminium powder. Both are important to attach electrical cable for cathodic protection and lightening protection process.
Testing Items and Testing Procedure
2 test specimens shall the sectioned transverse to the anode lead and 2 test specimens parallel with the anode lead. The specimens shall be prepared and etched for metallographic examination. The examination shall be performed at a magnification of 50X. The fusion line of the weld/brazing shall at any point not be more than 1.0 mm below the base material surface. Intergranular copper penetration of the base material shall not at any point extend beyond 0.5 mm from the fusion line.
4 HV10 hardness tests shall be made on each of the specimens for copper penetration measurements. A traverse shall be made across the weld/brazing zone. The traverse shall consist of minimum 6 indentations; two in the heat affected zone (HAZ) on each side of the weld/brazing, two in the HAZ under the weld/brazing and two in the base material on each side of the weld/brazing. The HAZ indentations shall be made as close to the fusion line as possible.
The maximum hardness shall not exceed the limits given in below as applicable for the intended service and type of material.
weld metal is:
— 325 HV10 for C-Mn and low alloy steels in non-sour service
— 250 HV10 for C-Mn and low alloy steels in sour service
(for weld caps not exposed to the sour service media, maximum of hardness of 275 HV10 may be agreed for base
material thickness > 12 mm)
— 325 HV10 for 13Cr martensitic stainless steels
— 350 HV10 for duplex stainless steels
— 325 HV10 for clad or lined material in non-sour service.
4 test specimen shall be mounted in a tensile testing machine and secured in the cable in one end and the base material in the other end. Force shall be applied until the specimen breaks. The specimen shall break in the cable.
The electrical resistance of each test weld/brazing shall not exceed 0.1 Ohm
Each test weld/brazing shall be securely fixed and tested with a sharp blow from a 1.0 kg hammer. The weld/brazing shall withstand the hammer blow and remain firmly attached to the base material and show no sign of tearing or cracking
Production requirements for welding/brazing of anode leadsThe anode cable attachments shall be located at least 150 mm away from any weld.
- For cable preparation cable cutters shall be used. The insulation shall be stripped for the last 50 mm of the cable to be attached. The conductor core shall be clean, bright and dry. Greasy and oily conductor cores shall be cleaned with residue free solvent or dipped in molten solder. Corroded conductor cores shall be cleaned to bright metal with brush or other means. Wet conductor cores shall be dried by rapid drying residue free solvent, alcohol or hand torch.
- The cable attachment area, and for pin brazing also the equipment earth connection area, shall be cleaned for an area of minimum 50 mm × 550 mm. All mill scale, rust, grease, paint, primer, corrosion coating, and dirt shall be removed and the surface prepared to finishing degree St 3 according to ISO 8501-1. The surface shall be bright, clean and dry when welding/brazing is started.
- Production testing
- Each welded/brazed anode lead shall be subjected to electrical resistance test and mechanical strength test according to acceptance criteria
- Repair of welded/brazed anode leads
- Welded/brazed anode leads not meeting the requirements shall be removed and the affected area shall be removed by grinding.
- For welded/brazed anode leads that are attached directly onto pressure containing parts the ground areas shall blend smoothly into the surrounding material. Complete removal of defects shall be verified by local visual inspection and polishing and etching to confirm removal of copper penetration.
- The remaining wall thickness in the ground area shall be checked by ultrasonic wall thickness measurements to verify that the thickness of the remaining material is more than the specified minimum. Imperfections that encroach on the minimum permissible wall thickness shall be classified as defects.
Digest of DNV-RP-F101 SUBMARINE PIPELINE SYSTEMS