Duplex 2205 & Inconel 825 Steam Generators for Air Products NPK Hydrogen Project — ASME U Stamp Certified

How Lmart delivered two corrosion-resistant steam generators for a world-leading industrial gas producer’s syngas reforming plant.

Customer	Air Products and Chemicals, Inc. (NYSE: APD)
Industry	Industrial Gas / Hydrogen Production
Project	NPK Project
Product	Steam Generator (蒸汽发生器)
Quantity	2 units
Unit Dimensions	DN762 × THK10 × L2285 mm, 1,560 kg each
Design Standard	ASME Section VIII Division 1, U Stamp
Shell Material	SB424 N08825 (Inconel 825) / Duplex 2205
Tube Material	N08825 (Inconel 825)
Application	Steam generation for syngas steam reforming
Key Outcome	On-time delivery with full ASME documentation; established basis for repeat orders across 14+ global Air Products projects

Customer Background & Industry Context

Air Products is one of the world’s largest industrial gas companies, operating in over 50 countries with a market cap exceeding $60 billion. Their hydrogen and syngas production plants are among the most demanding operating environments in the process industry. These facilities run continuously at elevated temperatures and pressures, processing gas streams containing hydrogen sulfide, carbon dioxide, and steam — a combination that strips away standard carbon steel and most stainless steels within years.

The NPK Project required steam generators positioned directly in the syngas reforming loop. Their function is straightforward in principle: generate the high-purity steam that feeds into the reforming reactors. In practice, the operating conditions are severe. Tube-side and shell-side fluids alternate between corrosive gas streams and high-temperature steam. A failure here does not just mean unplanned downtime. It means a complete plant shutdown, hazardous release risk, and repair costs that dwarf the original equipment budget.

For a company of Air Products’ standing, equipment reliability is non-negotiable. Their procurement teams specify exotic alloy materials precisely because they have learned the cost of material underperformance over decades of plant operation. Getting the material selection and fabrication right the first time is what distinguishes a qualified vendor from a supplier.

Challenges & Pain Points

Designing and fabricating these steam generators posed four distinct technical challenges.

1. High-temperature sulfidation and corrosion resistance. Syngas streams carry sulfur compounds that aggressively attack ferritic and austenitic stainless steels at elevated temperatures. The shell and tube material had to resist both aqueous corrosion at lower temperatures during startup and shutdown cycles, and sulfidation attack at operating temperatures. Inconel 825 (N08825) was specified for tube fabrication because of its demonstrated resistance to these conditions — but welding nickel alloys to achieve full code compliance requires a different approach than welding carbon steel or standard 316L.

2. Shell construction with SB424 plate in duplex. The shell material specification combined SB424 N08825 plate with Duplex 2205. Duplex 2205 offers higher strength than standard austenitic grades, which allows thinner shell walls without sacrificing pressure containment. However, duplex stainless steel requires precise interpass temperature control during welding to maintain the austenite/ferrite phase balance. Deviation from the qualified WPS (Welding Procedure Specification) leads to a microstructure that is susceptible to pitting and stress corrosion cracking — the exact failure mode the material is supposed to prevent.

3. Tube-to-tubesheet joint integrity. In a steam generator handling corrosive process fluids, the tube-to-tubesheet joint is the most critical weld joint in the assembly. Any leak path at this interface introduces process gas into the steam side or vice versa. Air Products required full-strength weld joints with radiographic examination — not the minimal expanded-plus-seal-weld often acceptable in lower-risk applications.

4. ASME code compliance with full documentation. Air Products’ global procurement standard requires the complete ASME data package: Manufacturer’s Data Report (Form U-1), Certified Design Calculations, Material Test Reports (MTRs) traceable to the mill certificate, NDE reports, and the Hydrostatic Test record. The U Stamp Authorized Inspector (AI) must witness and sign off at defined hold points. Managing this documentation package — while keeping fabrication moving — requires a quality management process that most fabricators simply do not have in place for nickel alloy work.

Why Air Products Chose Lmart

Lmart holds the ASME Certificate of Authorization (U Stamp) for pressure vessel fabrication, administered under a Quality Control System that is audited by the National Board of Boiler and Pressure Vessel Inspectors. This is not a paperwork exercise. It means Lmart operates with qualified WPS/PQR documentation covering carbon steel, low-alloy steel, austenitic stainless steels, duplex stainless steels, and nickel alloys including N08825 — all pre-qualified before the first inquiry arrives.

The more important factor, however, was track record. By the time the NPK Project was awarded, Air Products had already placed orders with Lmart across multiple projects covering heat exchangers, pressure vessels, and specialty equipment. That history — 16+ units delivered across 14 global projects at the time of the NPK award — provided the procurement team with direct evidence of fabrication quality, documentation discipline, and delivery reliability.

Air Products does not award repeat business to vendors who meet the minimum bar. The continued relationship reflected Lmart’s ability to handle nickel alloy fabrication at the quality level their engineering team expects. For the NPK steam generators specifically, Lmart’s demonstrated welding capability on N08825 and Duplex 2205 was the deciding qualification criterion.

Engineering & Manufacturing Solution

The design of the two steam generators centered on a shell-and-tube configuration optimized for the operating pressure, temperature, and fluid combination specified in Air Products’ data sheets.

Shell construction. The shell was fabricated from SB424 N08825 plate rolled and longitudinally welded, with Duplex 2205 used for select structural components where the combination of corrosion resistance and higher yield strength was required. All shell welds were executed under qualified Welding Procedure Specifications developed specifically for dissimilar and duplex alloy joining, with interpass temperature strictly monitored and recorded on the traveler documents accompanying each vessel through the shop.

Tube bundle and tube-to-tubesheet joints. Tubes were sourced as N08825 seamless drawn tubes with full traceability to mill MTRs. Tubesheet material was matched to the tube alloy to avoid galvanic incompatibility at the joints. Tube-to-tubesheet welding was performed by certified welders holding qualification records for P-45 (nickel alloy) base metals. All tube-to-tubesheet welds were full-penetration fusion welds, inspected by liquid penetrant testing (PT) and supplemented with radiographic testing (RT) at a sampling rate defined in the Inspection and Test Plan (ITP) agreed with Air Products and the Authorized Inspector.

Thermal cycling design. Steam generators in reforming service experience significant thermal cycling during plant startups, shutdowns, and load changes. The design incorporated adequate flexibility in the tube bundle to accommodate differential thermal expansion between the shell and tubes, minimizing stress accumulation at the tubesheet joints over the vessel’s intended service life.

Material traceability. Every piece of material used in the pressure boundary — plate, tubes, flanges, fittings — was received with mill MTRs, cross-checked against the ASME SB and SA material specifications, and tagged with heat and lot numbers carried through fabrication to the final Data Report. No material substitution or downgrading occurred at any stage.

Why Inconel 825? Material Selection Rationale

Property	316L SS	Inconel 825 (N08825)	Inconel 625 (N06625)
SCC Resistance	Poor — fails in chloride environments	Excellent	Superior
Pitting Resistance (PREN)	~25	~33	~51
Max Service Temp	~450 °C	~540 °C	~650 °C
Weldability	Excellent	Good — requires qualified WPS	Good — requires qualified WPS
Relative Material Cost	1×	3–4×	6–8×
Typical Application	General chemical service	H&sub2;/syngas, high-purity gas, sulfuric acid	Subsea, ultra-high corrosion

For this service — high-purity hydrogen generation with mixed acid condensate — Inconel 825 provides the required corrosion resistance at roughly half the cost of Inconel 625, making it the engineering-optimal choice.

Project Execution, QC & Delivery

Fabrication was executed under Lmart’s ASME-compliant Quality Control System with the following hold and witness points managed in coordination with the Authorized Inspector:

• Material receiving inspection — dimensional check, MTR review, positive material identification (PMI) using XRF analyzer on all nickel alloy materials
• Fit-up inspection — joint geometry and root gap verified before welding
• Preheat and interpass temperature monitoring — recorded continuously for duplex and nickel alloy joints
• NDE — radiographic testing of longitudinal and circumferential shell seams; PT on tube-to-tubesheet welds
• Hydrostatic test — performed to 1.3× MAWP per ASME VIII-1 requirements, witnessed by the AI
• Final dimensional inspection — all nozzle orientations, overall length, and weight confirmed against the certified drawing
• Documentation package — U-1 Data Report signed by AI and Manufacturer, delivered with full MTR traceability, NDE reports, and hydrostatic test record

The complete documentation package was submitted to Air Products’ project team prior to shipment, allowing their QA team to review and close out the inspection dossier without delays at the receiving end.

Both units were delivered on schedule, meeting the project’s fabrication milestone.

Results & Business Impact

The two NPK steam generators entered service as part of Air Products’ hydrogen production facility, providing reliable steam generation for the syngas reforming loop. The selection of N08825 for the tube bundle and SB424 N08825/Duplex 2205 for the shell gave the plant operator confidence in a service life appropriate for a baseload production asset.

From a business relationship standpoint, the NPK Project represented one chapter in an ongoing partnership rather than a one-time transaction. Across 14 global projects, Air Products and Lmart have jointly delivered more than 16 units covering a range of pressure vessel and heat exchanger configurations. Each completed project reinforces the supply chain qualification that Air Products’ global procurement requires — and reduces the friction cost of evaluating a new vendor for each inquiry.

For Lmart, this relationship demonstrates a clear capability position: the ability to execute exotic alloy fabrication under ASME code with the documentation discipline that Tier 1 industrial gas companies require. That position is not built on price. It is built on consistent technical execution and zero NCR (non-conformance report) history across the relationship.

Customer Voice

Air Products selected Lmart for this project based on demonstrated capability and placed the order through a competitive qualification process — the strongest form of supplier endorsement in capital equipment procurement.

“The NPK project steam generators came through with a complete ASME documentation package and on-time delivery. Lmart understands what a world-class quality audit looks like, and they deliver the paperwork to match the hardware. That matters when you are commissioning a hydrogen plant on a fixed schedule.”

— Project Manager, Air Products NPK Project (paraphrased from project review feedback)

Note: Lmart respects client confidentiality. Specific contact references are available upon request during the qualification process.