2 Oversized Carbon Steel Vessels for Air Products Ulsan 6: DN4500 Chiller Water Tower and 24-Meter Direct Contact After Cooler — ASME U + KGS Dual Certification

Lmart fabricated two large-format carbon steel pressure vessels for Air Products’ Ulsan 6 hydrogen/syngas plant in South Korea — a DN4500 chiller water tower weighing 29.5 tons and a 24-meter-long direct contact after cooler at 61.5 tons. Both vessels are built to ASME U stamp with KGS (Korean Gas Safety Corporation) certification for domestic installation in one of Asia’s largest petrochemical complexes.

Customer	Air Products and Chemicals, Inc.
Industry	Industrial gases — hydrogen & syngas production
Project	Ulsan 6 (A1700) — hydrogen/syngas plant at Ulsan Petrochemical Complex, South Korea
Equipment	Chiller Water Tower × 1, Direct Contact After Cooler × 1 (2 units total, 91,050 kg combined)
Design Code	ASME Section VIII, Division 1 (U Stamp) + KGS
Key Material	SA-516 Gr. 70 (carbon steel, normalized)
Max Diameter	DN4500 (4,500 mm / ~177″)
Max Length	24,000 mm T/T (~79 ft) — Direct Contact After Cooler
Max Unit Weight	61,500 kg (61.5 metric tons) — Direct Contact After Cooler

Customer Background and Industry Context

Air Products and Chemicals, Inc. is one of the world’s largest industrial gas companies, headquartered in Allentown, Pennsylvania, with operations in over 50 countries. The company is a leading supplier of hydrogen, helium, nitrogen, oxygen, and syngas to the refining, petrochemical, semiconductor, and energy industries. Air Products operates under a build-own-operate model for many of its large-scale gas supply plants, where it designs, constructs, and operates on-site facilities under long-term supply contracts with major industrial customers.

The Ulsan Petrochemical Complex in South Korea is one of the largest integrated industrial zones in the world, home to major refineries and chemical plants operated by SK Innovation, S-Oil, Hanwha, and others. Air Products’ Ulsan 6 (Project A1700) is a hydrogen and syngas plant within this complex, providing high-purity hydrogen and synthesis gas to downstream refining and chemical processes. The plant uses steam methane reforming (SMR) technology, where natural gas is reacted with steam at high temperature to produce hydrogen and carbon monoxide, followed by shift conversion, purification, and compression.

In this process chain, the chiller water tower and direct contact after cooler serve critical roles in syngas cooling and water separation downstream of the reformer and shift converter. The direct contact after cooler removes process heat from the raw syngas stream through direct water quenching, while the chiller water tower further cools and conditions the gas before it enters the PSA (Pressure Swing Adsorption) purification unit. Both vessels operate with large gas volumes, significant thermal loads, and process water circulation — hence the large diameters and overall dimensions.

Challenges and Engineering Pain Points

Large-Format Fabrication: DN4500 and DN4000 Diameters

Vessels at DN4500 (4.5-meter diameter) and DN4000 (4-meter diameter) exceed the capabilities of many pressure vessel fabricators. Rolling SA-516 Gr. 70 plate in thicknesses of 10–20 mm to these diameters requires plate rolls with sufficient opening width and bending force, and the resulting shell sections must maintain roundness tolerances per ASME UG-80 — typically ≤ 1% of nominal diameter, or ±45 mm on a DN4500 shell. Fit-up of circumferential seams between shell courses at these diameters demands precision fixturing and alignment tooling to prevent angular misalignment and peaking at weld joints, both of which affect fatigue life and radiographic acceptance.

61.5-Ton Vessel at 24 Meters Overall Length

The direct contact after cooler — DN4000 × 16/20 × 24000 mm T/T at 61,500 kg — presents significant handling and fabrication challenges. A 24-meter vessel cannot be rotated in a standard positioner; it requires dedicated rail-mounted roller beds with synchronized drive systems for welding rotation. The 61.5-ton lift weight during shop assembly, hydrostatic test (with water fill adding approximately 300 m³ of additional mass), and load-out requires crane capacity planning and engineered lift procedures. Transportation from the workshop to the port for export to Korea adds further logistical complexity — oversize road permits, route surveys for bridge clearances, and multi-axle trailer configuration.

Variable Wall Thickness Construction

Both vessels use variable wall thickness in their shell sections — the chiller water tower at 10/12 mm and the after cooler at 16/20 mm. This design approach optimizes material usage by matching wall thickness to the pressure and loading conditions at different elevations or zones within the vessel. However, it introduces additional fabrication complexity: transition zones between different shell thicknesses require tapered welds per ASME UW-9 to avoid stress concentration at the thickness discontinuity. Each thickness change point becomes a critical inspection location for radiographic examination.

ASME U + KGS Dual Certification

Korean domestic installation requires compliance with Korea Gas Safety Corporation (KGS) regulations in addition to the ASME U stamp. KGS certification involves third-party inspection oversight by an authorized Korean inspection body, review of design calculations against Korean regulatory requirements, witness of pressure testing, and approval of the Manufacturer’s Data Report. The dual certification path requires parallel documentation systems — ASME forms (U-1, U-1A) alongside KGS-specific documentation — and coordinated inspection scheduling to ensure both ASME Authorized Inspector and KGS representative are present at hold points.

Why Air Products Selected Lmart

Large-format fabrication capacity. Lmart’s workshop accommodates vessels up to 6-meter diameter and 50+ meter overall length, with overhead crane capacity rated for the 61.5-ton after cooler at full assembly weight. The plate rolling, welding positioner, and heat treatment facilities are sized for the heavy-wall, large-diameter shells required by Air Products’ process vessel specifications.

ASME + KGS dual certification experience. Lmart holds ASME U stamps and has an established track record with KGS-certified vessels for Korean installation. The dual-certification workflow — coordinating ASME AI and KGS inspector schedules, maintaining parallel documentation, and meeting both code requirements simultaneously — is a routine capability, not a first-time exercise.

Export logistics for oversized vessels. Shipping 24-meter, 61.5-ton vessels from Jiangsu Province to Ulsan, South Korea, requires integrated logistics planning — oversize road transport from the Zhangjiagang workshop to the nearest deep-water port, heavy-lift loading onto ocean-going vessels, and customs documentation for Korean import with KGS pre-clearance. Lmart’s logistics team manages this end-to-end for Korean, Japanese, and Southeast Asian export projects.

Established relationship with Air Products. This project builds on a supply relationship that includes the Samsung P Project (air receivers, desulfurizers, PSA vessels, and other process equipment also delivered to Korean sites under ASME U + KGS certification). Repeat business from a global EPC like Air Products reflects consistent quality performance and delivery reliability across multiple project cycles.

Engineering and Manufacturing Solution

The two vessels were engineered as part of Air Products’ standard SMR plant equipment package, with Lmart executing fabrication to Air Products’ approved drawings and specifications.

SA-516 Gr. 70 — the workhorse carbon steel for process vessels. SA-516 Grade 70 is a carbon-manganese-silicon steel plate specifically intended for moderate- to lower-temperature service in welded pressure vessels. With a minimum tensile strength of 485 MPa (70 ksi) and minimum yield of 260 MPa, it provides the strength required for these large-diameter vessels at manageable wall thicknesses. The normalized condition ensures uniform grain structure and consistent mechanical properties across the heavy plates used in these vessels — particularly important for the 20 mm thick sections in the after cooler, where through-thickness properties affect joint efficiency and impact toughness.

Chiller water tower (1FE-C171). The DN4500 × 10/12 × 13796 mm T/T chiller water tower weighs 29,550 kg. The dual wall thickness (10 mm upper section, 12 mm lower section) reflects the hydrostatic head distribution in a vessel operating with water circulation. Internal components include water distribution trays or packing support systems that ensure uniform gas-liquid contact for cooling efficiency. The 13.8-meter tangent-to-tangent length provides sufficient residence time for heat and mass transfer between the syngas stream and the circulating cooling water.

Direct contact after cooler (1FE-C161). At DN4000 × 16/20 × 24000 mm T/T and 61,500 kg, this is the larger of the two vessels by a significant margin. Direct contact after coolers work by spraying process water directly into the hot syngas stream, achieving rapid cooling through evaporative heat transfer. The 24-meter length accommodates multiple quench stages, water collection and redistribution sections, and mist elimination internals at the gas outlet. The 16/20 mm variable wall construction places heavier plate in the lower sections where operating pressure combines with hydrostatic head from the water inventory, while the upper (gas-phase) sections use 16 mm plate where loads are lower.

Complete Equipment Specifications

#	Item No.	Equipment	Qty	Material	Size (DN × THK × L T/T)	Weight (kg)	Certification
1	1FE-C171	Chiller Water Tower	1	SA-516 Gr. 70	DN4500 × 10/12 × 13796	29,550	ASME U + KGS
2	1FE-C161	Direct Contact After Cooler	1	SA-516 Gr. 70	DN4000 × 16/20 × 24000	61,500	ASME U + KGS
Total						91,050

Dimensional Context: How Large Are These Vessels?

Parameter	Chiller Water Tower	Direct Contact After Cooler
Diameter	4.5 m (~15 ft)	4.0 m (~13 ft)
Length (T/T)	13.8 m (~45 ft)	24.0 m (~79 ft)
Weight	29.5 metric tons	61.5 metric tons
Approximate Volume	~220 m³	~300 m³
Comparable Scale	Width of a 2-lane road × 4-story building height	Width of a highway lane × length of a Boeing 737 fuselage

Project Execution, Quality Control, and Delivery

Fabrication of these two oversized vessels required careful sequencing of shop floor operations, with the 24-meter after cooler occupying a dedicated bay throughout its production cycle.

Key QC milestones for each vessel:

• Incoming material verification: SA-516 Gr. 70 plate mill certificates reviewed against ASME SA-20 supplementary requirements, mechanical test coupons verified for tensile, yield, and Charpy impact properties
• Shell plate rolling to ASME UG-80 roundness tolerances with dimensional checks at each course — critical at DN4000/4500 diameters where minor out-of-roundness compounds through multi-course assembly
• Longitudinal and circumferential seam welding with 100% radiographic examination per ASME UW-51 for full joint efficiency
• Transition zone welds between variable-thickness shell sections: tapered per UW-9, RT examined, and measured for profile compliance
• Nozzle-to-shell welds: full penetration welds with RT or UT examination depending on nozzle diameter and orientation
• Post-weld heat treatment (PWHT) in dedicated furnace — the 24-meter after cooler required a furnace of corresponding length with multi-zone temperature monitoring to ensure uniform soak temperature across the full vessel length
• Hydrostatic pressure test at 1.3× MAWP per ASME UG-99, with ASME Authorized Inspector and KGS representative present as witness
• Final dimensional survey, NDE summary, and dual documentation package (ASME U-1/U-1A + KGS forms)

Export logistics for these two vessels required multi-axle hydraulic trailers for the 35 km road transport from Lmart’s Zhangjiagang workshop to the Yangtze River port facility, followed by barge transfer to a deep-water port for ocean shipment to Ulsan, South Korea. The 61.5-ton after cooler, at 24 meters in length, required a dedicated route survey to confirm bridge clearances and turning radii along the transport corridor.

Results and Business Impact

Both vessels were delivered to the Ulsan 6 project site on schedule, enabling Air Products to maintain its commissioning timeline for the hydrogen/syngas plant. The chiller water tower and direct contact after cooler are now integral components of the Ulsan 6 process train, handling syngas cooling and conditioning for one of the largest industrial gas supply operations in the Korean market.

For Air Products, this project reinforces Lmart as a qualified fabricator for large-format process vessels destined for Korean installation — a market with strict KGS regulatory requirements that limit the pool of acceptable international suppliers. The Ulsan 6 scope, combined with the Samsung P Project equipment delivered through the same supply chain, establishes a proven fabrication and logistics pathway for future Air Products projects in Korea.

For Lmart, the Ulsan 6 project demonstrates large-format fabrication capability at the upper end of the shop’s dimensional range — DN4500 diameter and 24-meter length at 61.5 tons. These dimensions and weights represent a class of work that relatively few Asian fabricators can execute with ASME U stamp quality and the logistical infrastructure for Korean export delivery.

Customer Voice

Air Products has placed multiple orders with Lmart across Korean projects, including the Ulsan 6 scope described here and the Samsung P Project involving air receivers, desulfurizers, PSA vessels, steam generators, and other process equipment — a procurement pattern that reflects sustained confidence in Lmart’s fabrication quality and delivery performance.

“The fabrication quality and documentation met our requirements for both ASME and KGS certification without rework or re-inspection.”

— Air Products project engineering (paraphrased from project close-out review)

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