Seamless chrome-moly pipe stops being practical somewhere above NPS 24 and heavy wall, where piercing a billet that size is beyond most mills, so large steam and hydrogen lines are rolled from alloy plate and welded along the seam instead. The plate decides the grade. ASTM A691 EFW pipe is made from chrome-moly plate, usually to ASTM A387, formed and electric fusion welded, then heat treated and radiographed to the class ordered. It carries main steam and hydroprocessing lines at plants across Oman. Seamless grades are on the alloy and chrome-moly pipes and tubes hub.
Where A691 Pipe Is Used
- Main steam and hot reheat lines in large power plants, above practical seamless sizes
- Hydroprocessing transfer lines in refineries, in hydrogen service
- Reformer and heater transfer piping in petrochemical and fertilizer plants
- Large headers and manifolds in high-temperature service
- Replacement spools matching existing EFW alloy piping
For sizes that seamless mills can supply, ASTM A335 pipe is normally preferred, since there is no seam to inspect or qualify.
A691 Grades and Classes
An A691 order has two parts, and both must be stated.
Grade describes the steel, and matches the chrome-moly plate it is rolled from:
A691 grade | Nominal composition | Seamless equivalent |
|---|---|---|
1/2CR | ½Cr-½Mo | P2 |
1CR | 1Cr-½Mo | P12 |
1-1/4CR | 1¼Cr-½Mo | P11 |
2-1/4CR | 2¼Cr-1Mo | P22 |
5CR | 5Cr-½Mo | P5 |
9CR | 9Cr-1Mo | P9 |
91 | 9Cr-1Mo-V-Nb | P91 |
Class describes what was done to the pipe after welding: whether it was heat treated and how much of the weld seam was radiographed. Classes run from the basic level up to fully heat treated and fully radiographed pipe. Code piping normally calls for a class with both heat treatment and complete radiography, and the class changes both the price and the weld joint efficiency used in design, so it belongs on every enquiry.
Welding, PWHT and Sour Service
A691 pipe carries a longitudinal seam, so any sour or hydrogen service assessment has to cover the weld and its heat-affected zone as well as the body. Under NACE MR0175 / ISO 15156-2, hardness must be within the applicable limit throughout, which depends on correct post-weld heat treatment. For hot hydrogen, material selection follows API RP 941 for the grade concerned. State any sour or hydrogen requirements in the RFQ; they are confirmed at quotation.
Certificates and Inspection
A691 pipe is supplied with EN 10204 3.1 certificates as standard, and EN 10204 3.2 certificates on request. Inspection by the buyer's nominated third-party agency can be arranged; state your requirement in the RFQ. The package should include the plate certificate, the welding procedure and consumable details, heat treatment records, radiographic reports for the seam, hydrostatic test results and dimensional records. See the MTC and EN 10204 certification guide.
How A691 Pipe Is Made
- Alloy plate, normally to ASTM A387 in the matching grade and class, is cut to size.
- The plate is rolled into a cylinder, and the longitudinal seam is joined by electric fusion welding, usually submerged arc.
- Large diameters may be made from more than one plate, adding circumferential seams.
- The pipe is heat treated according to the class ordered.
- The seam is radiographed to the extent the class requires, and the pipe is hydrostatically tested.
Because the base material is plate, the mill certificate should trace back to the plate heat, and the weld procedure and filler metal should be recorded alongside it.
A691 Pipe Price Factors
- Grade and class, since heat treatment and radiography both add cost
- Diameter, wall and plate thickness available
- Quantity, and whether plate has to be rolled specially
- Impact testing, ultrasonic testing of plate and other supplementary tests
- PMI and hardness requirements
- Certification (EN 10204 3.1 or 3.2) and third-party inspection
- Break bulk freight and destination port
Quotations are available in USD, OMR, AED, SAR, QAR, KWD and BHD, on EXW, FOB, CFR or CIF terms.
What to send for a quotation: grade, class, OD, wall, length, quantity, end finish, radiography and testing requirements, certification, inspection, destination port and required date.
Handling Large-Diameter Alloy Pipe
Lead time is confirmed at quotation. A691 pipe is shipped with bevel protectors and, where specified, internal bracing to protect large thin-walled sections from ovality during transport. It should be lifted with soft slings or padded hooks, never chains against the bevel. On Gulf sites, store it off the ground with ends capped, keep each grade in a marked stack, and protect the bevels from sand until fabrication.
Fittings for A691 Lines
Match the pipe grade with ASTM A234 WP11, WP22, WP5, WP9 or WP91 buttweld fittings and ASTM A182 F-grade flanges:
- Alloy steel fittings and flanges hub
- Alloy steel welded EFW pipes and tubes
- Alloy steel seamless pipes and tubes
A691 pipe is used across power generation, refinery and petrochemical and fertilizer plants.
ASTM A691 FAQ
What is A691 pipe?
Carbon and alloy steel pipe made by rolling plate and welding the seam by electric fusion welding, for high-pressure service at high temperature. Alloy grades are rolled from chrome-moly plate, usually ASTM A387.
What do A691 classes mean?
The class states whether the pipe was heat treated after welding and how much of the seam was radiographed. It affects the weld joint efficiency used in design, so it must be specified.
How does A691 compare with A335 seamless pipe?
A335 has no seam and is preferred where seamless sizes are available. A691 covers larger diameters and heavier walls than seamless mills can produce, at the cost of a seam to inspect.
Which A691 grade matches P22?
Grade 2-1/4CR is the 2¼Cr-1Mo equivalent of P22. Grade 1-1/4CR matches P11, and Grade 91 matches P91.
Can A691 be used in hydrogen service?
Yes, with grade selection to API RP 941 and the seam properly heat treated and inspected. State the service conditions in the RFQ.
What should I send for an A691 quotation?
Send the grade, class, OD, wall, length, quantity, end finish, testing requirements, certification, inspection, destination port and required date.
Request a Quote for ASTM A691 EFW Pipe
Send the grade, class, diameter, wall and quantity, with the piping specification attached. Every enquiry is checked against ASTM A691 before the offer is prepared, so a missing class, which changes both price and design joint efficiency, is settled at the start.