ASME Steam Generator in Inconel 825 for Float Glass Hydrogen Supply — Air Products / Pilkington Project

When a world-leading flat glass manufacturer needed a corrosion-proof steam generator that could run 24/7 in a hydrogen-rich atmosphere, Lmart delivered an ASME U-stamp vessel in N08825 alloy — on schedule, with zero rework.

End Customer	Pilkington (NSG Group)
EPC / Buyer	Air Products
Product	Steam Generator
Weight	1,560 kg
Dimensions	DN762 × THK10 × L2,285 mm
Design Standard	ASME Section VIII Div. 1 — U Stamp
Shell Material	SB424 N08825 (Inconel 825) / Duplex 2205
Tube Material	N08825 (Inconel 825)
Application	Industrial gas / hydrogen supply for float glass tin bath and annealing furnace
Delivery	On schedule

Customer Background

Pilkington, a flagship brand of the NSG Group, is one of the world’s most recognized names in flat glass manufacturing. The company’s float glass process — the industry standard for producing high-quality architectural and automotive glazing — demands extraordinary process control. In the tin bath, molten glass floats across a precisely maintained surface of liquid tin at temperatures exceeding 1,000 °C. To prevent oxidation of the tin and contamination of the glass surface, the atmosphere inside the tin bath enclosure must be maintained with a protective mixture of nitrogen and hydrogen.

Downstream, annealing lehrs cool the freshly formed glass ribbon through controlled temperature gradients. Any deviation in atmosphere purity — even trace concentrations of oxygen or moisture — can cause surface defects that render entire production runs unusable.

Air Products, a global industrial gas leader, supplies and manages the hydrogen and nitrogen infrastructure serving Pilkington’s production facility. Their scope included specifying and procuring a steam generator capable of operating reliably within this demanding environment. The unit needed to interface directly with high-purity gas systems and meet the most rigorous pressure vessel code requirements available: ASME Section VIII Division 1, U Stamp.

The Challenges

Continuous 24/7 Production — Zero Planned Downtime

Float glass lines do not stop. A Pilkington production line operates continuously for years between planned shutdowns. Any auxiliary equipment failure — including the steam generator — cascades immediately into production disruption. The specification demanded a vessel engineered not merely to code minimums, but to a standard where unplanned maintenance is effectively eliminated for the design life of the unit.

Hydrogen-Rich, High-Temperature Atmosphere

Operating in proximity to hydrogen supply systems introduces two distinct material threats. At elevated temperatures, atomic hydrogen can diffuse into ferritic and carbon steel microstructures, causing hydrogen embrittlement or hydrogen-induced cracking over time. Separately, process-side fluids in steam generation applications often carry dissolved chlorides and sulfur compounds. Standard 304 or 316 stainless steels are susceptible to chloride stress corrosion cracking under these conditions — a failure mode that can develop invisibly before catastrophic rupture.

Zero Contamination Tolerance

The float glass process is exceptionally sensitive to contamination. Any corrosion product, oxide scale, or particulate entering the gas supply stream can deposit on the glass surface or compromise the tin bath, creating optical defects. This made internal surface quality and cleanliness of the steam generator a production-critical requirement — not merely a quality checkbox.

Dual-Material Specification Complexity

The specification called for an unusual material combination: N08825 (Inconel 825) for both the shell and tubes, with Duplex 2205 incorporated into the pressure-boundary construction. Sourcing certified plate and tube in these alloys, qualifying welding procedures for dissimilar-material joints, and maintaining traceability from mill certificate to finished weld are significantly more demanding than standard carbon steel fabrication. Few fabricators have the documented experience and certified procedures to execute this combination under ASME U Stamp authorization.

Why Lmart

Air Products’ procurement team evaluated several fabricators capable of ASME U Stamp work. Lmart was selected on three primary criteria.

Alloy Fabrication Credentials. Lmart holds active ASME U Stamp authorization and has an established track record with high-nickel alloys including Inconel 825, Hastelloy C-276, and Duplex stainless steels across heat exchanger and pressure vessel projects for the chemical, petrochemical, and industrial gas sectors. Documented WPS/PQR records for N08825 welding were available prior to contract award, eliminating qualification lead time.

Engineering Collaboration. Rather than treating the specification as a fixed input, Lmart’s engineering team engaged Air Products’ process engineers during the pre-order phase to review nozzle orientation, support saddle design, and thermal expansion provisions. This upstream collaboration identified two minor interface issues that were resolved on paper — avoiding costly field modifications.

Delivery Reliability. With a continuous float glass line on the other end of the supply chain, schedule slippage was not negotiable. Lmart’s project management approach — fixed material procurement deadlines, weekly internal milestone tracking, and proactive communication with the client on NDE scheduling — provided Air Products with the confidence that on-time delivery was a managed outcome rather than a hope.

Engineering Solution

The steam generator is a vertical shell-and-tube configuration, optimized for the thermal duty and spatial envelope defined by Air Products’ system layout.

Shell: SB424 N08825 plate, 10 mm wall, DN762 nominal diameter, 2,285 mm shell length. Inconel 825 was selected for its outstanding resistance to corrosion in reducing and oxidizing environments, its resistance to chloride-induced stress corrosion cracking, and its stability at elevated temperatures. Where Duplex 2205 was incorporated into the pressure boundary, weld joint design and preheat procedures followed Lmart’s qualified WPS to ensure metallurgical integrity at the dissimilar interface.

Tubes: N08825 seamless tubes, fully consistent in alloy chemistry with the shell to minimize galvanic risk at the tubesheet joints. Tube-to-tubesheet joints were welded and expanded, providing both a positive mechanical lock and a metallurgically bonded seal.

Tubesheet and Nozzles: Material selection extended to all pressure-boundary components. Nozzle reinforcement pads, flanges, and attachments were specified in compatible alloy grades to eliminate any carbon steel or lower-alloy intrusion into the corrosion-sensitive flow path.

Internal Cleanliness Protocol: Following hydrotest, the vessel interior was flushed, dried, and inspected to cleanliness standards appropriate for high-purity gas service. All temporary supports and fabrication aids were removed and inspected for completeness prior to closure.

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.

Quality Control and Inspection

Every pressure vessel fabricated under Lmart’s ASME U Stamp authorization operates under a documented Quality Control program subject to third-party Authorized Inspector oversight. For this project, the QC milestones included:

• Material Verification: Full traceability from mill test reports (MTR) for all N08825 and Duplex 2205 pressure-boundary materials, verified against ASME Section II requirements prior to cutting.
• WPS/PQR Qualification: All welding performed by ASME-qualified welders under pre-qualified or project-qualified Welding Procedure Specifications.
• NDE: Radiographic testing (RT) of longitudinal and circumferential seam welds in accordance with ASME Section VIII Div. 1 UW-51 requirements. Liquid penetrant testing (PT) on all N08825 and dissimilar welds.
• Hydrotest: Hydrostatic pressure test at 1.3× MAWP, witnessed by the Authorized Inspector, with documented pass result.
• Data Report: ASME Form U-1 completed and registered, providing the end customer with a permanent legal record of code compliance.

The Authorized Inspector issued no NCRs (non-conformance reports) during the fabrication sequence. The vessel passed hydrotest on the first attempt.

Results

The steam generator was delivered to Air Products on the contracted schedule. Installation and commissioning at the Pilkington facility proceeded without incident. Key outcomes:

• Zero rework during fabrication — NDE results were clean at first inspection on all weld seams.
• On-schedule delivery — no impact to Air Products’ commissioning timeline or Pilkington’s production schedule.
• Full ASME U Stamp documentation package delivered with the vessel, satisfying both Air Products’ procurement requirements and Pilkington’s site compliance records.
• Material traceability dossier provided, covering all pressure-boundary materials from mill certificate through completed weld map — a requirement for high-purity gas service applications.

The unit is operating in continuous service, supporting hydrogen supply to Pilkington’s float glass tin bath and annealing systems.

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 material handling and weld quality on the N08825 vessel exceeded what we typically see in this alloy class. Lmart’s team engaged with our process engineers early, and the documentation package was exactly what we needed for site compliance. We had zero surprises at commissioning — which, for a project connected to a continuous glass line, is the only acceptable outcome.”

— Plant Manager, Pilkington Production Facility (paraphrased from project review feedback)

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