Description / Abstract: Material Description. This standard covers double wall construction tubing wherein the two walls and the joints are copper brazed in a reducing atmosphere to produce tubing satisfactory for hydraulic brake lines, lubrication oil lines, vacuum lines, air brake lines, etc. There are requirements for the base metal, the optional coating materials, and the coated tubing. These requirements are applicable to the product coming out of the tube mills and the coating application lines, which are sometimes separate facilities. This tubing is used in the production of customized parts and assemblies. It is recommended that those parts and assemblies be validated for corrosion performance, conductivity and continuity, strength, appearance, and other critical properties unique to the particular application.

Symbols. Not applicable.

Applicability. Double wall steel tubing is typically used for automotive hydraulic brake lines.

Remarks. Double wall steel tubing should not be used for fuel lines because residual copper can contribute to the formation of sour gas.

Tubing Designation Code. It is recommended that the codes in Section 3 be used on drawings and purchase orders to designate tubing type, outside diameter, wall thickness, and manufacturing process.