1.Size: 4-1/2"~20"
  Steel grade: J55, K55, N80, L80, P110,Q1255)
  Specification: API SPEC 5CT
2.Quality control
  We have implemented stringent quality control tests
  system to inspect raw materials and examine products in
  every stage of the production :
  *Size and surface inspection
  *Non-destructive test
  *Thread inspection
  *Hydrostatic test
  *Drifting test
  *Physical and chemical analysis
  *Hardness and pressure test