What ASTM A671 CD80 Class 71 Pipe Is
ASTM A671 is the standard specification for electric-fusion-welded (EFW) pipe produced from pressure-vessel-quality plate with filler metal added, for atmospheric and lower-temperature service. CD80 Class 71 is one of the class conditions covered by that numbering system: the letter pair and grade define the plate from which the cylinder is rolled, and the class defines how the finished pipe is heat treated, examined and tested before release.
The designation A671 CD80 Class 71 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.
Class 71 belongs to the higher-numbered group of class conditions. These classes are ordered far less often than the lower-numbered groups, and the additional heat treatment and examination content that they call for has a direct effect on price and lead time. Availability of a specific high-numbered class is therefore best settled at the enquiry stage, with the class number written out in full in the enquiry, the quotation and the purchase order.
Manufacturing Route and Quality Control
Plate is purchased against the referenced pressure-vessel plate specification, with chemical and mechanical certificates traced to each heat.
Plate edges are machined or planed, the shell is formed, and the longitudinal joint is prepared 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, from one or both sides.
The class heat treatment is applied to the finished pipe before straightening and end finishing.
Radiography of the longitudinal seam is performed to the coverage required by the class, and weld ends and repaired areas are examined by magnetic particle or liquid penetrant methods.
Each length is hydrostatically tested, marked with the full designation and released with a mill test report and the inspection records for the order.
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
Pipes of this type are used in LNG and natural gas plants, air separation and industrial gas facilities, refrigeration and ethylene units, low-temperature petrochemical and chemical process lines, and cold sections of gas processing trains. Where a project specifies a higher-numbered class, the reason is usually a combination of design minimum temperature, wall thickness and the examination level required by the owner's material specification, rather than a difference in the plate itself.
Ordering, Fabrication and Inspection Points
Because a single digit separates one class from the next, requisitions should state the full designation and repeat the intended heat treatment and radiographic coverage in words. Project material specifications that are more restrictive than the product standard take precedence, and any such difference should be recorded on the order so that the mill can plan the heat treatment and examination sequence.
Fabrication follows a welding procedure qualified to ASME BPVC Section IX, with low-hydrogen consumables and controlled preheat and interpass temperature. Traceability should be maintained from the plate certificate through forming, welding, heat treatment and final examination, so that the class condition claimed on the release document can be demonstrated for each individual length.
FAQ
Q: How does class 71 differ from class 50 on the same plate grade?
The classes differ in the heat-treatment condition and in the examination and testing regime required for the finished pipe. The plate designation is identical, but the class changes what is done to the pipe after welding, so the two are not interchangeable without checking the design requirements.
Q: Is a high-numbered class always available?
Not necessarily. Higher-numbered classes are ordered less often and may require additional heat-treatment or examination steps, which affects lead time. It is good practice to confirm availability and the delivery schedule at the enquiry stage, with the class number stated in full.
Q: What governs acceptance at low temperature?
Impact properties of the weld metal and heat-affected zone at the design minimum temperature govern acceptance for low-temperature service, together with the tensile properties of the pipe. The impact test temperature and minimum absorbed energy should be stated explicitly in the order.
Q: Which sizes and wall thicknesses can be produced?
Plate-based EFW pipe is normally produced from NPS 8 to NPS 48 with outside diameters per ASME B36.10M, in wall thicknesses well beyond the range of standard line pipe, and in lengths of approximately 6 m to 12 m or to specific cut lengths.
Q: What should be checked on delivery?
Check the marking against the purchase order, the mill test report against the specified plate grade and class, and the dimensional records against the stated tolerances. The heat number on the pipe should match the heat number on the certificate.
Q: How is the seam protected during transport?
Bevelled ends and weld preparations are protected with end caps or rings, and the pipe is supported to avoid point loading. External coating, where ordered, is applied after all mill welding and testing are complete.
