1. The structure: Api standard inner tube and the outer surface of the threaded couplings deposited tungsten alloy layer. 2. The performance indicators: The basic properties: size, precision thread sealing meet api standards. Threaded connection: thread has good release buckle sex. Corrosion properties: anti h2s / co2 temperature corrosion resistance to salt water corrosion, alkali, corrosion resistance, weak acid corrosion, nace 0177 to meet the standard requirements for corrosion resistance. Tungsten alloy layer and the substrate binding: according to gb / t5270-2005 testing, coating does not crack, not falling. Appearance: uniformly bright, silvery white Tungsten alloy layer thickness: