ASME Section I

Applies to Equipment & Systems:

• Power Boilers (PG) — Steam boilers generating steam or vapor at pressures exceeding 15 psig [100 kPa ga].
• High-Temperature Water (HTW) Boilers (PG) — Water boilers operating at pressures exceeding 160 psig [1,100 kPa ga] and/or temperatures exceeding 250 °F [120 °C].
• Electric Boilers (PE) — Power boilers where the heat source is electricity (immersion elements or electrode boilers).
• Miniature Boilers (PM) — Small boilers with shell ID ≤ 16 in [400 mm], gross volume ≤ 5 cu ft [140 L], heating surface ≤ 20 sq ft [1.9 m²], and operating pressure ≤ 100 psig [700 kPa ga].
• Heat Recovery Steam Generators (HRSGs / HFG) — Boilers generating steam using high-temperature exhaust gas from gas turbines or industrial process furnaces.
• Organic Fluid Heaters (PVG) — Vaporizers using organic heat transfer fluids operated at pressures > 15 psig or temps > 250 °F.
• Boiler External Piping (BEP) — Critical steam, feedwater, blowdown, drain, and instrument piping connecting directly to the boiler drum/header up to and including the boundary block valves.

Exact BEP vs NBEP Jurisdictional Boundaries:

• Main Steam Piping: Extends from the boiler drum/superheater outlet header up to and including the first stop valve (or main steam isolation valve - MSIV).
• Feedwater Piping: Extends from the boiler inlet back to and including the second stop valve (or check valve + stop valve combination).
• Blowdown / Drain Lines: Extends from the drum/header connections up to and including the second stop/blowoff valve.
• Water Column, Level Gauge & Instrument Piping: All connections up to and including the second isolation valve or instrument block valve.
• Overpressure Relief Piping: From the drum/superheater nozzle up to the inlet flange of the safety relief valve (valve itself is Section I stamped).

Does NOT Cover (Exclusions & Alternative Codes):

• Heating Boilers (ASME Section IV) — Low-pressure steam boilers (≤ 15 psig) and hot-water heating boilers (≤ 160 psig and ≤ 250 °F).
• Unfired Pressure Vessels (ASME Section VIII) — Heat exchangers, unfired steam drums, accumulators, and gas/oil separators.
• Non-Boiler External Piping (NBEP - ASME B31.1) — Balance-of-plant steam, condensate, and water piping located downstream of the BEP boundary stop valves.
• Process Piping (ASME B31.3) — Chemical, refinery, and petrochem piping beyond the boiler island boundaries.
• Fired Process Heaters (API STD 560 / ASME Section VIII) — Direct-fired tubular process heaters used in petroleum refining and petrochemical plants.

ASME Section I enforces strict legal and engineering mandates to guarantee structural integrity and overpressure protection:

• Third-Party Authorized Inspection (AI): Mandatory third-party quality oversight by a commissioned Authorized Inspector (AI) employed by an accredited Authorized Inspection Agency (AIA). The AI inspects designs, material certifications, welding, NDE, hydrotests, and signs the official Manufacturer's Data Reports (Forms P-2, P-3, P-4, P-4A).
• Approved Materials & Traceability (Part PG): Pressure-retaining components (shells, drums, headers, tubes, piping) must strictly utilize materials permitted by ASME Section II (Parts A, B, and D). Mill Test Reports (MTRs) and strict material identification transfer during cutting are legally required.
• Pressure Design & Wall Thickness (PG-27): Strict design formulas for tubes, drums, shells, and headers under internal pressure. Incorporates ligament efficiency factors (PG-52) for perforated drums/tubesheets and joint efficiencies (PG-29).
• High-Temperature Creep Metallurgy: Strict selection and PWHT protocols for advanced creep-resistant alloys (SA-335 P91/P92, SA-213 T91/T92, SA-213 TP304H/TP347H/Super304H) used in high-temperature superheaters, reheaters, and main steam headers.
• Welding Procedure & Welder Qualification (Part PW): All pressure-retaining welding must follow qualified Weld Procedure Specifications (WPS) and Procedure Qualification Records (PQR) certified per ASME Section IX. Welders must hold valid WPQ performance qualifications.
• Post-Weld Heat Treatment (PWHT - PW-39): Mandatory stress relief heat treatment based on material P-Number and nominal thickness, specifying strict heating rates, soak temperatures, and cooling limits.
• Nondestructive Examination (NDE - PW-11 & Section V): Mandatory Radiographic Testing (RT) or Ultrasonic Testing (UT) for main longitudinal and circumferential drum welds, headers, and thick-wall BEP joints. Magnetic Particle (MT) or Liquid Penetrant (PT) for attachments and fillet welds.
• Overpressure Protection & Safety Valves (PG-67 to PG-73): Every boiler must have at least one safety valve (or two or more if heating surface > 500 sq ft or electric input > 1,100 kW). Safety valves must be NB-certified, Section I "V" stamped, set at or below MAWP, and capable of discharging all steam generated without pressure exceeding MAWP by > 6%.
• Hydrostatic Pressure Test (PG-99): Completed boilers and BEP spools must undergo a mandatory hydrostatic test at 1.5× the Maximum Allowable Working Pressure (MAWP) prior to stamping. Water temperature must be kept between 70 °F [20 °C] and 120 °F [50 °C] to prevent brittle fracture.
• ASME Code Symbol Stamping & MDR: Upon AI approval and hydrotest completion, the official ASME Code Symbol Stamp must be applied to the boiler plate/nameplate:
  • "S" — Power Boilers
  • "PP" — Pressure Piping (BEP)
  • "A" — Assembly of Power Boilers
  • "E" — Electric Boilers
  • "M" — Miniature Boilers
  • "V" — Boiler Safety Valves

ASME Section I is structured into clear mandatory parts and appendices that govern design, construction, and inspection.

Section I Code Structure & Organization

• Part PG — General Requirements for All Construction Methods
• Part PW — Requirements for Boilers Fabricated by Welding
• Part PR — Requirements for Boilers Fabricated by Riveting (Historical)
• Part PB — Requirements for Boilers Fabricated by Brazing
• Part PFT — Requirements for Firetube Boilers
• Part PWT — Requirements for Watertube Boilers
• Part PE — Requirements for Electric Boilers
• Part PM — Requirements for Miniature Boilers
• Part PVG — Requirements for Organic Fluid Vaporizers
• Part HFG — Requirements for Fired and Unfired Steam Generators (HRSGs)

Key Mathematical Design Formulas (Part PG)

1. Cylindrical Shell & Header Minimum Thickness (PG-27.2.2)

For cylindrical shells, drums, and headers under internal pressure:

t = (P × D_o) / (2S × E + 2y × P) + C

Where:

• t = Minimum required thickness of shell or header (in)
• P = Maximum Allowable Working Pressure (MAWP) (psig)
• D_o = Outside diameter of shell or header (in)
• S = Maximum allowable stress value at design temperature from ASME Section II Part D (psi)
• E = Weld joint efficiency factor (PG-29) or ligament efficiency (PG-52)
• y = Temperature coefficient (y = 0.4 for T ≤ 900 °F, adjusting up to 0.7 for high-temperature ferritic/austenitic steels)
• C = Allowance for threading, grooving, or corrosion (in)

2. Tube Thickness Formula (PG-27.2.1)

For boiler tubes, superheater tubes, and reheater tubes under internal pressure:

t = (P × D_o) / (2S + P) + 0.005 × D_o + e

Where e is the thickness allowance for bending or threading.

3. Ligament Efficiency Calculation (PG-52)

When holes are drilled into a drum or header for tube placement, the strength of the metal between holes (ligament) is reduced:

• Longitudinal Ligament Efficiency (E):

E = (p - d) / p

Where p = pitch of tube holes (in) and d = diameter of tube holes (in).

• Diagonal Ligament Efficiency: Calculated using ASME Section I Fig. PG-52 diagrams when tube holes are arranged in staggered pattern.

Boiler External Piping (BEP) Valve Configuration Rules

High-Temperature Creep Metallurgy in Power Boilers

Modern power plants operate at supercritical (SC) and ultra-supercritical (USC) conditions (T > 1050 °F / 565 °C, P > 3500 psig / 24 MPa). Section I mandates strict material selection and heat treatment:

• Carbon Steels (SA-106 Gr. B, SA-210 Gr. A1): Used for economizers, lower drums, and low-temp feedwater below 800 °F [425 °C].
• Low-Alloy Steels (SA-335 P11, P22 / SA-213 T11, T22): Used for steam headers and superheaters operating between 800 °F and 1050 °F.
• Creep-Strength Enhanced Ferritic (CSEF) Steels (SA-335 P91, P92 / SA-213 T91, T92): Modified 9Cr-1Mo-V alloys designed for high creep-rupture strength up to 1150 °F [620 °C]. Requires strict normalization, tempering, and tight PWHT temperature control (1300 °F - 1400 °F) to avoid premature Type IV creep failure in HAZ.
• Austenitic Stainless Steels (SA-213 TP304H, TP347H, Super304H): Used for high-temperature superheater/reheater tubes subject to fireside corrosion and high creep temperatures up to 1200 °F+.

ASME Manufacturer's Data Reports (MDR)

• Form P-2: Manufacturer's Data Report for All Types of Boilers Except Water Tube Boilers and Electric Boilers.
• Form P-3: Manufacturer's Data Report for Watertube Boilers, Superheaters, and Waterwalls.
• Form P-4: Manufacturer's Data Report for Complete Boiler Units.
• Form P-4A: Manufacturer's Data Report for Fabricated Piping (BEP).
• Form P-6: Certificate of Field Assembly.