In the refining, petrochemical, and power generation industries, welding quality and post weld heat treatment (PWHT) are critical factors affecting the long-term safety and performance of astm a691 alloy steel pipes.
With over 20 years of manufacturing and quality control experience, LONGMA provides a detailed explanation of ASTM A691 welding and PWHT requirements, offering practical guidance for engineers and procurement teams to ensure compliance and reduce project risks.
Key Standards and Technical Basis
- ASTM A691– Specifies the manufacturing, heat treatment, and inspection requirements for electric-fusion-welded (EFW) alloy steel pipes for high-pressure, high-temperature service.
- ASME Section IX & Section V– Define requirements for welding procedure qualification (WPS/PQR) and nondestructive examination (NDE) methods.
- For chromium–molybdenum alloys (e.g., astm a691 grade 2.1 4cr, equivalent to 2.25Cr–1Mo), standards emphasize preheating, controlled heat input, and regulated PWHT parametersto ensure structural integrity.
Welding and PWHT Requirements
| Item | Key Point | Recommended LONGMA Specification (T/C Wording Example) |
| Preheating / Interpass Temperature | For Cr–Mo alloys, preheat to avoid cold cracking; control interpass temperature based on thickness. | “For P22 / astm a691 grade 2.1 4cr, preheat to 150–250°C, interpass ≤300°C (see WPS for details).” |
| Filler Metal Selection | Use filler metals matching base metal composition; avoid hard, brittle microstructures. | “Filler material shall meet ASME/ASTM chemistry requirements and be supplied with MTC certification.” |
| Heat Input Control | Excessive heat input leads to coarse grains and reduced toughness; control and record heat input. | “Heat input (kJ/mm) shall be recorded and verified during PQR testing.” |
| PWHT Temperature & Holding Time | ASTM A691 Table 2 specifies PWHT ranges; hold time should be at least 1 h/in. (or 1 h minimum). | “For Class 20–23 pipes, PWHT as per ASTM A691 Table 2, holding ≥1 h/in (or 1 h minimum), with complete furnace chart record.” |
| Cooling and Tempering | For high-alloy grades (e.g., 9Cr), controlled cooling and tempering prevent retained austenite. | “After PWHT, cool to ≤150°C before any further processing per WPS requirements.” |
Note:
ASTM A691 Table 2 clearly defines PWHT temperature and holding times for each grade/class. These parameters must be referenced directly in procurement specifications.
Typical PWHT Parameters (for Reference)
| Grade / Class | Typical PWHT Temperature Range | Minimum Holding Time |
| P22 / astm a691 grade 2.1 4cr (2.25Cr–1Mo) | 650–700°C (refer to Table 2) | ≥1 h/in or ≥1 h (whichever is greater) |
| P9 / High Cr Alloy | Higher PWHT temperature with controlled cooling | As per ASTM A691 & WPS |
| Lower Grades / Thin Wall Pipes | May require only normalization or no PWHT | Based on project & ASTM A691 requirements |
Procurement documents should state: “PWHT shall be carried out per ASTM A691 Table 2, with temperature and time control as per approved WPS.”
Inspection Methods and Acceptance Standards
To reduce material risk and ensure compliance, it is recommended that all inspection methods and acceptance criteria be clearly defined in the Technical Contract (T/C).
| Test Item | Purpose | Execution Procedure | Standard Reference |
| Chemical Composition (OES) | Verify base & filler metal chemistry | Test each heat/batch using OES, attach MTC | ASTM A691 / ASTM A20 |
| Tensile Test | Confirm yield and tensile strength | Conduct per ASTM A370, at room/high temp | ASTM A370 |
| Impact Test (CVN) | Evaluate weld toughness and ductility | Charpy V-notch at 0°C or –20°C | ASTM A370 (Appendix) |
| Nondestructive Testing (UT/RT) | Detect weld or internal flaws | 100% UT or partial RT per ASME V | ASTM A691 §7.3 / ASME Section V |
| PWHT Records | Verify furnace temperature/time curve | Provide furnace data, charts, and calibration logs | ASTM A691 Table 2 |
| PMI Verification | Prevent material mix-up | 100% or random PMI before shipment | ASTM E1476 |
Including clauses for non-conformance handling, third-party witnessing, and repair or replacement procedures in the contract helps minimize project risk and ensures supplier accountability.
LONGMA’s Capabilities — Why Choose LONGMA
LONGMA’s in-house laboratory provides full-scope quality control from raw material to PWHT verification, including:
- Testing Equipment:Optical Emission Spectrometer (OES), universal tensile machines, impact testers, full-automatic UT/RT systems, and data-recorded PWHT furnaces.
- Full Documentation:Each astm a691 pipe is supplied with MTC, WPS/PQR, PWHT furnace charts, NDT reports, and PMI records.
- Third-Party Witnessing:Fully open to SGS, BV, or TÜV inspections.
- Export Experience:Extensive project record for astm a691 pipes & tubes in spain, Europe, and the Middle East, with proven quality and on-time delivery.
These strengths demonstrate LONGMA’s ability to not only meet but exceed ASTM and ASME standards for alloy steel pipe fabrication and heat treatment.
Procurement Recommendations
For project specifications and procurement contracts, LONGMA recommends including the following clauses:
- ASTM A691 Reference:“PWHT shall comply with ASTM A691 Table 2; minimum holding time 1 h/in or 1 h, whichever is greater.”
- Grade-Specific Controls:For astm a691 grade 2.1 4cr, define preheat/interpass temperatures, filler material grade, PWHT range, and third-party witness rights.
- Documentation Requirement:Supplier shall provide complete MTC, WPS/PQR, PWHT charts, NDT & PMI reports with shipment.
This ensures full technical traceability and eliminates disputes during inspection or commissioning.
Conclusion
Proper welding and PWHT control are essential for the performance and service life of ASTM A691 steel pipes in high-pressure and high-temperature environments.
With its advanced laboratory, automated production lines, and extensive international project experience, LONGMA ensures that every astm a691 pipe meets stringent quality standards and project specifications.
For global projects — including astm a691 pipes & tubes in spain — LONGMA provides not only premium-quality materials but also complete technical documentation and after-sales support, ensuring safety, compliance, and confidence in every purchase.
