Application
Alloy 316L seam welded pressure tubing in the heat treated condition is typically used in oil and natural gas wells for applications including hydraulically actuated surface-controlled subsurface safety valves, chemical injection, and instrumentation. In such applications, it is commonly referred to as control line tubing.

The tubing is generally deployed by strapping it to the outside of the production casing. It may be encapsulated and can be included along with other pressure tubing or TEC 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 316L is a chromium-nickel austenitic stainless steel with an addition of molybdenum and reduced carbon content. The addition of molybdenum provides improved resistance to pitting and crevice corrosion in environments containing halides such as chlorides when compared to so-called conventional 18 chromium 8 nickel austenitic stainless steels such as 304L. The reduced carbon content minimizes harmful chromium carbide precipitation during welding and thereby improves resistance to intergranular corrosion. Austenitic stainless steels such as 316L are susceptible to stress corrosion cracking (SCC) in environments containing chlorides and other halides. Alloy 316L is generally used in oil and gas production environments which do not contain oxygen and have limited amounts of chlorides and hydrogen sulfide. Consult ISO 15156-3, Table A.2 for the limits regarding alloy 316L 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 join lengths of cold rolled strip to enable long lengths between orbital welds (greater than 5,000 ft. between orbital welds is achievable).

The strip is formed into a tubular cross section and longitudinally seam welded using either the gas tungsten arc (GTAW) or laser beam welding (LBW) process. The tubing may be welded at a larger outside diameter, sunk to final size and subsequently heat treated. Heat treated tubing is joined by orbital welding to achieve the desired length. The final material condition of the tubing is heat treated.

Mechanical properties, permissible variation in tubing dimensions and size dependant characteristics / properties are listed in Tables 3, 4, and 5 on reverse respectively.

Nondestructive Testing (NDT)
Eddy current testing (ECT) is performed on the longitudinally seam welded tubing and strip splice welds in the as-heat treated condition. Radiographic testing and ECT are performed on material in the final heat treated condition. Radiographic testing is performed on all orbital welds and those strip splice welds detected by ECT. Yield pressure hydrostatic testing is performed on the heat treated tubing at final size.

Standards and Specifications
Tubing Specification PTM-TS-004, Alloy 316L Tubing for Control Line Applications
ASTM A269, Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Service
Meets the material limits for 316L austenitic stainless steel listed in ISO 15156-3, Table A.2