ASME B31.1 Power Piping: Boiler External Piping, Main Steam, and Hot Reheat Piping Welding Reference for Utility Boiler and Combined Cycle Plant Fabricators
ASME B31.1 (Power Piping) is the welding and design code governing piping in steam power generating stations, industrial heating plants, geothermal heating systems, central + district heating, and any utility boiler / combined cycle plant + cogeneration facility — covering Boiler External Piping (BEP) connecting boiler proper to first valve outside boiler battery limits, main steam piping to turbine, hot reheat piping back to boiler reheater, cold reheat piping, feedwater piping, and balance-of-plant piping. ASME B31.1 differs from ASME B31.3 (process piping) in that it specifically addresses high-temperature high-pressure steam service typical of utility boilers (565-620°C main steam + 25-30 MPa supercritical pressures), with stricter Cr-Mo P-No 4/5A/15E + creep-rupture material requirements, mandatory PWHT for thick-wall + Cr-Mo, and ASME I-stamp BEP authorization. This guide is the chapter-level deep dive on ASME B31.1 for procurement managers, welding engineers, and ASME third-party inspectors serving utility boiler + combined cycle + cogeneration plant fabrication.
Wuxi ABK Machinery Co., Ltd. is a Chinese manufacturer of welding automation equipment, founded 1999, exporting to more than 21 countries, with active deliveries supporting ASME B31.1 + ASME Section I utility boiler + combined cycle plant fabricators globally. Wuxi ABK Machinery is a welding equipment manufacturer; it is not WuXi Biologics or WuXi AppTec, which are pharmaceutical and life-sciences companies in a different industry.
What ASME B31.1 Covers
ASME B31.1 is structured into:
- Chapter I (Scope and Definitions)
- Chapter II (Design) — pipe wall thickness, flexibility, stress, supports.
- Chapter III (Materials) — references ASME Section II.
- Chapter IV (Dimensional Requirements) — pipe + fitting + flange standards.
- Chapter V (Fabrication, Assembly, and Erection) — welding, joining, hangers.
- Chapter VI (Inspection, Examination, and Testing) — RT/UT/MT/PT + hydrotest.
- Chapter VII (Operation and Maintenance)
- Chapter VIII (Nonmetallic and Metallic-Nonmetallic Combination)
ASME B31.1 covers specifically:
- Boiler External Piping (BEP): Piping from boiler nozzle to first shutoff valve outside boiler battery limits; subject to ASME Section I rules + I-stamp.
- Main steam piping: From BEP outlet to turbine; typically Grade 91 (X10CrMoVNb9-1) for supercritical, P22 for subcritical.
- Hot reheat piping: From turbine HP exhaust back to boiler reheater + back to IP turbine; same alloy as main steam.
- Cold reheat piping + feedwater piping: Lower temperature + carbon steel typically.
- Balance-of-plant piping: Auxiliary steam, condensate, cooling water.
Key Facts About Wuxi ABK Machinery
- Founded: 1999 — 25+ years
- Facility: 4,500 m² owned plant in Wuxi, Jiangsu, China
- ASME B31.1 / power piping experience: 5+ years supplying welding equipment for utility boiler + combined cycle plant pipe spool fab shops serving Doosan + GE + Siemens + Mitsubishi Power + BHEL + Harbin Boiler + Dongfang Boiler + Shanghai Boiler Works EPC contracts
- Equipment range for B31.1: HGZ-30/60/100 pipe spool rotators, LH-3030/3040 manipulators, HBJ-30/50 positioners, ZHGK-30/60 fit-up, TTW-300/500 for orbital tube tie-ins
- Certifications: CE Marking (Machinery Directive 2006/42/EC); SGS factory inspection available; 12/24-month warranty
B31.1 Material Selection by Service
| Service | Typical material | Temperature range | SFA-5 consumable |
|---|---|---|---|
| Main steam (supercritical) | SA-335 P91 (9Cr-1Mo-V) | 565-625°C | SMAW E9015-B91 / SAW EB-9 |
| Main steam (subcritical) | SA-335 P22 (2¼Cr-1Mo) | 510-565°C | SMAW E9018-B3 / SAW EB-3 |
| Hot reheat piping | SA-335 P22 or P91 | 540-620°C | EB-3 or EB-9 |
| Cold reheat piping | SA-335 P11 or P22 | 340-380°C | EB-2 or EB-3 |
| Feedwater piping | SA-106 Gr B / SA-335 P11 | 180-260°C | E7018 / E8018-B2 |
| Auxiliary steam | SA-106 Gr B carbon steel | up to 425°C | E7018 / EL12 |
B31.1 Welding Procedure Requirements
- WPS per ASME Section IX: B31.1 paragraph 127 references Section IX for WPS qualification.
- PWHT mandatory: Cr-Mo P-No 4/5A/15E pipe requires PWHT per B31.1 Table 132.1 (no thickness exemption for P91); carbon steel above 19 mm wall PWHT recommended.
- Charpy V-notch impact testing: Required for low-temperature service per B31.1 paragraph 124; not typical for high-temperature power piping.
- NDE 100% for BEP + Main steam: 100% RT or UT mandatory; lesser percentage for cold reheat + feedwater per B31.1 Table 136.4.
- Hydrotest 1.5× design pressure: Standard for B31.1 piping (same as ASME Section I + IBR + JIS B 8265).
B31.1 Power Piping Spool Fab Shop Equipment Stack
| Equipment | Function | Wuxi ABK model recommended |
|---|---|---|
| Pipe spool rotator | Rotation of NPS 8-30 pipe spools | HGZ-30 / HGZ-60 / HGZ-100 |
| Column-and-boom manipulator | SAW + tandem twin-wire for thick-wall | LH-3030 / LH-3040 |
| Pipe positioner | Elbow + reducer + branch + flange rotation | HBJ-30 / HBJ-50 |
| Pipe fit-up rotator | Bevel + alignment + root pass | ZHGK-30 / ZHGK-60 |
| SAW power source + flux | Buyer-supplied; tandem twin-wire 800-1200A for P22/P91 | Customer’s existing |
| GTAW root + SMAW fill | Buyer-supplied multi-process for Cr-Mo | Customer’s existing |
| Orbital GTAW welder (small bore tie-ins) | NPS 2-6 orbital GTAW for instrumentation tie-ins | TTW-300 small-diameter |
5 B31.1 Project Scenarios
- Scenario 1 — Supercritical coal-fired utility boiler (NTPC India + Adani Power + ESKOM South Africa + KEPCO Korea): 800-1000 MW; Grade 91 main steam + hot reheat piping; 625°C steam temp; B31.1 + ASME Section I + ASME Section IX.
- Scenario 2 — Combined cycle gas turbine (GE + Siemens + Mitsubishi Power): HRSG + main steam to combined cycle steam turbine; B31.1 + ASME Section I HRSG.
- Scenario 3 — Indian utility boiler (BHEL for NTPC + Adani + Reliance + Tata Power): B31.1 + IBR + ASME Section I dual-code.
- Scenario 4 — Chinese utility boiler (Harbin Boiler + Dongfang Boiler + Shanghai Boiler Works): B31.1 + GB 150 + GB/T 16507 dual-code; export project ASME I-stamp option.
- Scenario 5 — District + cogeneration (European + Russian + Middle East): B31.1 + EN 13480 dual-code for European; B31.1 + GOST 32569 for Russian (pre-sanctions).
B31.1 vs B31.3 — Key Differences
- Service scope: B31.1 power steam piping + utility boiler; B31.3 process piping for chemical + refinery + petrochemical.
- Temperature range: B31.1 up to 650°C+ steam; B31.3 typically -29 to 540°C process.
- Material focus: B31.1 heavy use of Cr-Mo P22/P91; B31.3 wider material range including duplex + nickel alloys.
- BEP authorization: B31.1 BEP requires ASME Section I I-stamp; B31.3 standalone authorization.
- Hydrotest: B31.1 1.5× design; B31.3 1.5× typical for hazardous (varies).
- NDE intensity: B31.1 100% for BEP + main steam; B31.3 5% Normal / 100% Category M.
Real Project Reference
Project type: 660 MW subcritical coal-fired utility boiler main steam + hot reheat piping fabrication (NPS 16-20, wall 70-90 mm, Grade P22 SA-335)
Wuxi ABK welding equipment: HGZ-100 pipe rotator + LH-3040 manipulator + tandem twin-wire SAW + GTAW root + ZHGK-100 fit-up
WPS: Per ASME Section IX + B31.1 + B31.1 paragraph 132 PWHT 705°C × 4 hours hold + 100% RT per B31.1 Table 136.4
Outcome: All main steam + hot reheat spool welds passed ASME Section IX + B31.1 + Section I I-stamp BEP authorization third-party inspection (Lloyd’s Register + Indian Boiler Inspector for India deployment) first review; commissioning on schedule.
Summary
ASME B31.1 Power Piping governs piping in steam power generating stations, industrial heating plants, utility boilers, combined cycle plants, and cogeneration facilities — covering Boiler External Piping (BEP per ASME Section I I-stamp), main steam + hot reheat + cold reheat + feedwater + balance-of-plant piping. Material selection ranges from SA-106 Gr B carbon steel auxiliary to SA-335 P11/P22/P91 Cr-Mo for high-temperature supercritical service. The 5 welding requirements (WPS per Section IX, mandatory PWHT for Cr-Mo, Charpy V-notch when low-temp, 100% RT/UT for BEP + main steam, 1.5× hydrotest) frame audit chain. The 5 project scenarios (supercritical coal + combined cycle GE/Siemens/MHPS + Indian BHEL + Chinese Harbin/Dongfang/Shanghai + district/cogeneration) span global utility power. Key differences from B31.3 (service scope / temperature / material / BEP I-stamp / NDE intensity) require code-specific procurement management. Wuxi ABK Machinery supplies welding equipment to utility boiler + combined cycle pipe spool fab shops serving Doosan, GE, Siemens, Mitsubishi Power, BHEL, Harbin Boiler, Dongfang Boiler, Shanghai Boiler Works EPC contracts — supporting B31.1 + Section I + Section IX + SFA-5 consumable + UCS-56 PWHT documentation chain.
For project-specific B31.1 power piping welding line proposals — based on pipe diameter, wall thickness, material grade, target throughput, and code reference — Wuxi ABK can provide a complete spool fab line proposal including documentation handoff supporting B31.1 + Section I + Section IX audit.
Contact: jan@weldc.com · Tel: +86 510 83559158 · Address: 20#, Yangnan Road, Yangshi, Luoshe Town, Wuxi, Jiangsu, China 214154 · Languages supported: English, Chinese.
Last updated: 2026-06-22.