Application: Alloy 625 seam welded sheathed tubing, which is commonly referred to as TEC, is typically used in oil, natural gas and geothermal wells to provide power and communication to down-hole gauges. TEC contains a core consisting of insulated electrical conductor(s) and/ or optical fiber(s). The tubing is generally deployed by strapping it to the outside of the production casing. However, it may also be free hanging (self-supporting) inside the production casing. It may be encapsulated and can be included along with pressure tubing and mechanical components, such as bumpers, within a flatpack. The tubing is frequently supplied as 5,000 to 35,000 ft. coils on a wooden or steel reel, depending on size.

Description: Alloy 625 is an austenitic nickel - chromium - molybdenum - niobium alloy (see Table 1 on reverse). The high alloy content enables alloy 625 to withstand severe aqueous corrosion environments. High molybdenum content (8.0 to 10.0%) makes the alloy very resistant to chloride pitting and crevice corrosion. High nickel content (58.0% min.) provides relative freedom from chloride ion induced stress-corrosion cracking. Alloy 625 has shown excellent corrosion resistance in oil and gas environments containing hydrogen sulfide, carbon dioxide and chlorides. Consult ISO 15156-3, Table A.14 for the limits regarding material type 4d in hydrogen sulfide containing environments for oil and gas production. Draka uses expert system software to assist customers in their selection of alloys for oil and gas environments.

Manufacturing Process and Resultant Properties: Strip splice welds, which are used to join lengths of cold rolled strip, enable long continuous lengths of tubing to be manufactured. The strip is formed into a tubular cross section around the core and longitudinally seam welded using the gas tungsten arc welding (GTAW) process. The tubing is seam welded at a larger outside diameter to protect the core and then sunk to final size. The final material condition of the tubing is cold worked. Mechanical properties, permissible variation in tubing dimensions and size dependant characteristics / properties are listed in Tables 3, 4, and 5 on reverse respectively. It should be noted that due to the rapid rate at which alloy 625 strain hardens (cold works), it may not be possible to meet the ISO 15156-3 limits on maximum yield strength and hardness.

Nondestructive Testing (NDT): In-process eddy current testing (ECT) is performed on the as-welded tubing and final ECT is performed on the as-sunk tubing. Visual examination is performed on all ECT indications. Performance of additional NDT is dependent upon both the type of core and specific customer requirements, and may include: electrical continuity, high voltage/bending, insulation resistance, optical time domain reflectometer, and high pressure nitrogen underwater.

Standards and Specifications: Tubing Specification PTM-TS-019, Alloy 625 Sheathed Insulated Electrical Conductors and Optical Fibers ASTM B704, Standard Specification for Welded UNS N06625, UNS N06219 and UNS N08825 Alloy Tubes