What ASTM A671 CF65 Class 22 Pipe Is
ASTM A671 covers electric-fusion-welded (EFW) pipe made from pressure-vessel-quality plate with filler metal added, written for atmospheric and lower-temperature service. A CF65 Class 22 pipe is a plate-based welded product: the cylinder is rolled from plate, the longitudinal seam is welded with filler metal, and the finished length is heat treated and examined according to the class stated in the order.
The designation A671 CF65 Class 22 reads in three blocks. The letter pair identifies the pressure-vessel plate specification from which the cylinder is rolled, and the number that follows the letters keeps the grade numbering of that plate specification. The two-digit class number states the heat-treatment condition of the finished pipe together with the non-destructive examination and testing regime that applies to it. The class number must always be quoted together with the plate letters and the grade, because pipes of identical chemistry can be supplied in different heat-treatment conditions and with quite different levels of radiographic examination of the longitudinal seam.
Plate specifications used for low-temperature pipe achieve their toughness in one of two ways. Fine-grain carbon steel practice, with controlled chemistry and normalising or similar heat treatment, covers service down to the lower end of the ordinary carbon range. Nickel-bearing plate grades extend the useful temperature further, because nickel improves the low-temperature toughness of the ferritic matrix. The letter pair in the designation identifies which plate specification applies, and the material certificate issued with the pipe shows the exact specification and grade that were used.
Manufacturing Route and Quality Control
Plate is purchased against the referenced plate specification, certified for chemistry and mechanical properties by heat.
Edges are machined, the shell is formed, and the longitudinal joint is aligned and tacked.
The seam is welded with filler metal, normally by submerged arc welding with carbon steel electrode and flux combinations classified under AWS A5.17 / SFA-5.17.
Class 22 heat treatment is applied to the finished pipe, followed by straightening and end finishing.
Radiography of the longitudinal seam is performed to the coverage required by the class, with magnetic particle or liquid penetrant examination of weld ends and repairs.
Each length is hydrostatically tested, marked and released with a mill test report that includes the heat-treatment record and the impact test results.
Specification and Dimensional Data
| Item | Reference or range |
|---|---|
| Product standard | ASTM A671, electric-fusion-welded pipe for atmospheric and lower-temperature service |
| Base material | Pressure-vessel-quality steel plate, identified by the letter pair in the designation |
| Outside diameter | NPS 8 to NPS 48 as standard, outside diameters per ASME B36.10M |
| Wall thickness | Selected against the order, up to 76 mm for heavy-wall service |
| Lengths | 6 m to 12 m, or specific cut lengths |
| Seam type | One or two longitudinal seams, welded with filler metal |
| Filler metal | Carbon steel electrode and flux combinations to AWS A5.17 / SFA-5.17 |
| Heat treatment | As stated by the class number in the designation |
| Examination | Radiography of the longitudinal seam and hydrostatic test as required by the class |
| End finish | Plain, bevelled or as ordered |
Service Applications
Pipe in this grade and class is used for LNG transfer and regasification lines, industrial gas storage and distribution, air separation cold boxes, refrigeration and ethylene circuits, low-temperature chemical process piping, and cold sections of gas treating and dehydration units. Class 22 pipe is also common where a project needs a heat-treated, radiographed plate pipe for moderate pressure at low temperature rather than the higher-strength grades used on large cryogenic headers.
Ordering, Fabrication and Inspection Points
The order should state the plate letter pair and grade, the class number, size and wall thickness, length and end finish, the design minimum temperature, the impact test temperature and minimum absorbed energy for both weld metal and heat-affected zone, radiographic coverage, hydrostatic test conditions and the coating system if any.
Welding is performed under a procedure qualified to ASME BPVC Section IX. For low-temperature nickel-bearing or fine-grain plate, the heat input range and interpass temperature should be controlled as qualified, and unwarranted weld repairs avoided, because repeated thermal cycles in the same area are a common cause of reduced toughness. Post-weld heat treatment of field joints, where required by the class or by the project, is controlled by a written procedure with recorded temperatures.
FAQ
Q: What does the CF65 block of the designation mean?
The letter pair identifies the pressure-vessel plate specification used for the cylinder of the pipe, and 65 follows the grade numbering of that specification. The plate certificate issued with the pipe states the exact specification and grade, so the designation can be verified against the material actually used.
Q: What does class 22 add to the pipe?
The class number defines the heat-treatment condition of the finished pipe and the examination and testing regime applied to it. Class 22 pipe is heat treated after welding and examined in accordance with the class, and both the treatment and the examination results are recorded on the mill test report.
Q: Which plate specifications are used for low-temperature pipe?
Either fine-grain carbon steel plate with controlled chemistry and heat treatment, or plate grades that contain nickel to improve toughness at low temperature. The choice depends on the design minimum temperature and on the thickness of the section.
Q: How should impact testing be specified?
State the design minimum temperature, the impact test temperature and the minimum absorbed energy, and require the test to cover the weld metal and heat-affected zone as well as the plate. Tensile properties alone do not demonstrate suitability for low-temperature service.
Q: Is this pipe suitable for high-temperature service?
It is intended for atmospheric and lower-temperature service. Where the design is governed by high-temperature service, plate-based pipe to ASTM A672 is normally specified instead, because that standard is written for high-temperature service at moderate temperatures.
Q: What documentation is supplied with the pipe?
A mill test report covering chemical analysis, tensile properties, the heat-treatment record and the examination performed, together with the hydrostatic test record and dimensional results where requested, all traced to the pipe and heat numbers marked on each length.
