5 Large-Diameter 316L Mixing Vessels and Jacketed Degassers for Wacker Chemie: Vacuum Service with Interior Mirror Polishing

Lmart delivered five 316L stainless steel process vessels to Wacker Chemie AG for their silicone polymer production operations in China — three 34m³ mixing vessels at DN3000 and two 3m³ jacketed degasser vessels, all designed for full vacuum service at −0.1/0.1–0.6 MPa and featuring interior mirror polishing to Ra ≤ 0.4 μm for polymer purity.

Customer	Wacker Chemie AG
End User	Wacker China Operations (Zhangjiagang / Nanjing)
Equipment	34m³ Mixing Vessel × 3 + 3m³ Degasser Vessel × 2
Total Quantity	5 units
Unit Weight	7,350 kg (mixing) / 2,480 kg (degasser)
Shell Dimensions	DN3000 × THK14 × L5833 mm (mixing) / DN1400 × THK16 × L3266 mm (degasser)
Design Code	GB/T 150
Material	316L — interior mirror polished (Ra ≤ 0.4 μm)
Service Conditions	Full vacuum (−0.1 MPa) / Low temperature (−10 °C)
Application	Silicone polymer mixing and degassing process

Customer Background and Industry Context

Wacker Chemie AG, headquartered in Munich, Germany, is one of the world’s leading manufacturers of silicones, polymer binders, polysilicon, and specialty chemicals. With annual revenues exceeding €6 billion and operations spanning more than 20 countries, Wacker ranks among the top three global silicone producers alongside Dow and Shin-Etsu.

Wacker’s China footprint is substantial. The company operates major production sites in Zhangjiagang (Jiangsu Province) and Nanjing, manufacturing silicone polymers, dispersible polymer powders, and specialty silanes for the Chinese and broader Asian market. These facilities are built to Wacker’s global standards — which means European-grade process hygiene, German engineering specifications adapted to Chinese manufacturing codes, and rigorous quality expectations at every tier of the supply chain.

Silicone polymer production demands exceptional cleanliness in process equipment. The monomers and intermediate polymers are sensitive to metallic contamination, surface roughness, and residual particulates that can affect molecular weight distribution, clarity, and end-product performance. This places specific requirements on vessel interior surface finish, weld quality, and the absence of crevices or dead zones where material can accumulate and degrade.

Challenges and Engineering Pain Points

Large-Diameter Shell Fabrication at DN3000

The 34m³ mixing vessels have a shell diameter of 3,000 mm — three full meters. At this scale, plate rolling becomes a precision operation: maintaining roundness tolerances across a 14 mm thick 316L shell requires carefully controlled rolling passes, tack welding sequences, and post-roll dimensional verification. Any out-of-roundness at this diameter creates fit-up problems at head-to-shell joints and compromises the vessel’s ability to sustain vacuum loading uniformly. At 7,350 kg per unit, these are substantial pieces of equipment that demand heavy-lift capability and large-footprint workshop space throughout fabrication.

Vacuum Service Design (−0.1 MPa External Pressure)

All five vessels operate under full vacuum conditions. Vacuum service inverts the typical pressure vessel design problem: instead of resisting internal burst pressure, the shell must resist external pressure collapse. For the DN3000 mixing vessels, this means the shell, heads, and all penetrations must be evaluated for buckling stability under external pressure per GB/T 150.3. Stiffening rings, head geometry selection, and nozzle reinforcement calculations are all governed by external pressure charts rather than the more straightforward internal pressure formulas. The 14 mm wall thickness on a 3-meter diameter shell reflects this vacuum design requirement.

Low Temperature Service (−10 °C) and Impact Testing

Both mixing vessels and degassers operate at minimum design temperatures of −10 °C. While 316L austenitic stainless steel inherently retains good toughness at cryogenic temperatures, the design code still requires verification through Charpy V-notch impact testing of base metal and weld metal at the minimum design temperature. All welding procedures must be qualified with impact test results demonstrating adequate absorbed energy at −10 °C, and production welds are subject to impact testing per the approved WPS/PQR package.

Interior Mirror Polishing for Polymer Purity

Wacker specified interior mirror polishing to Ra ≤ 0.4 μm across the entire wetted surface — shell, heads, nozzle internals, and weld surfaces. In silicone polymer service, surface roughness directly affects product quality: micro-cavities trap polymer residue between batches, creating cross-contamination and degradation nucleation sites. Achieving Ra ≤ 0.4 μm on 316L requires multi-stage mechanical polishing followed by electropolishing, with surface roughness measurements documented at grid points across every polished surface. Internal weld profiles must be ground flush before polishing to eliminate weld crown irregularities.

Jacketed Degasser Design for Thermal Control

The two 3m³ degasser vessels incorporate a full external jacket operating at −0.1/0.6 MPa and −10/160 °C. The jacket provides thermal control during the degassing process — heating the polymer to reduce viscosity and promote dissolved gas release, then cooling to stabilize the degassed product. The jacket-to-shell interface introduces additional engineering complexity: differential thermal expansion between inner shell and jacket, jacket closure weld inspection access, and the requirement to pressure test both the inner vessel and jacket space independently.

Why Wacker Selected Lmart

Geographic proximity. Lmart’s manufacturing campus is located in Zhangjiagang — the same city where Wacker operates one of its largest China production sites. This proximity enables Wacker’s engineering and quality teams to conduct in-person inspections during fabrication without the cost and scheduling overhead of long-distance travel. For equipment requiring interior polishing verification, on-site witness points are practical necessities, not formalities.

Established track record with Wacker. This mixing vessel and degasser project builds on a prior relationship. Lmart previously manufactured 18 duplex stainless steel (2205) heat exchangers for Wacker’s Zhangjiagang operations — a project that demonstrated Lmart’s capability in specialty alloy fabrication and its ability to meet European chemical company quality expectations under Chinese design codes.

Large vessel manufacturing capability. DN3000 shell rolling is not a capability available at every pressure vessel shop. Lmart’s plate rolling equipment, welding positioners, and workshop crane capacity are sized for vessels in this diameter range, allowing the 34m³ mixing vessels to be fabricated without subcontracting critical operations.

GB standard expertise for multinational clients. Wacker’s China plants are built to Chinese codes. Lmart’s engineering team is fluent in GB/T 150 design, Chinese pressure vessel registration requirements, and the intersection between Chinese code compliance and the supplementary quality expectations that European chemical companies layer on top of code minimums.

Engineering and Manufacturing Solution

The five vessels divide into two distinct engineering packages, each with its own design challenges and manufacturing sequences.

34m³ Mixing Vessels (3 units). These are body-only vessels — no jacket, no internal coils — operating at −0.1/0.1 MPa and −10/100 °C. The DN3000 shell is formed from 316L plate in 14 mm thickness, rolled in sections and joined with full-penetration longitudinal and circumferential butt welds. Shell roundness was verified at multiple stations during rolling and after welding. Dished heads were formed to GB/T 150 standard profiles, with crown radius and knuckle radius verified against code requirements. All internal welds were ground flush to prepare for the multi-stage polishing sequence.

3m³ Degasser Vessels (2 units). These jacketed vessels operate at higher pressures (−0.1/0.6 MPa on both body and jacket) and higher temperatures (−10/200 °C body, −10/160 °C jacket). The 16 mm shell thickness on a DN1400 body reflects the higher external pressure rating and the additional structural demand of supporting the jacket. The jacket was fabricated as a separate shell assembled over the inner vessel, with jacket closure welds positioned to allow radiographic or ultrasonic examination access. Jacket inlet and outlet nozzles were positioned for optimal thermal fluid distribution.

Interior polishing process. After all welding and pressure testing, the interior surfaces of all five vessels underwent a controlled polishing sequence: coarse grinding to remove weld discoloration and surface scale, progressive mechanical polishing through increasingly fine abrasive grades, and final electropolishing to achieve the specified Ra ≤ 0.4 μm surface finish. Surface roughness was measured using a portable profilometer at documented grid locations, with all readings recorded in the final quality dossier.

Complete Equipment Specifications

Parameter	34m³ Mixing Vessel (× 3)	3m³ Degasser Vessel (× 2)
Volume	34 m³	3 m³
Type	Body Only	Jacketed
Unit Weight	7,350 kg	2,480 kg
Shell Diameter (DN)	3,000 mm	1,400 mm
Shell Thickness	14 mm	16 mm
Overall Length	5,833 mm	3,266 mm
Shell Material	316L	316L
Body Design P/T	−0.1 / 0.1 MPa · −10 / 100 °C	−0.1 / 0.6 MPa · −10 / 200 °C
Jacket Design P/T	N/A	−0.1 / 0.6 MPa · −10 / 160 °C
Interior Finish	Mirror polish Ra ≤ 0.4 μm	Mirror polish Ra ≤ 0.4 μm
Design Code	GB/T 150	GB/T 150

Project Execution, Quality Control, and Delivery

Production sequencing was organized to maximize workshop efficiency: the three DN3000 mixing vessels were rolled and welded in parallel using adjacent bays, while the two smaller degasser vessels followed a staggered schedule to allow jacket fit-up and independent pressure testing of both inner vessel and jacket compartments.

Key QC milestones for each vessel:

• Incoming material verification: 316L plate mill certificates checked against GB/T 4237 requirements, PMI verification on all plates
• Shell rolling dimensional check: roundness measured at minimum 4 stations per shell course, verified against GB/T 150 tolerances
• Weld examination: 100% radiographic examination on all longitudinal and circumferential butt welds
• Charpy V-notch impact testing at −10 °C on production weld coupons and base metal samples
• Hydrostatic pressure test per GB/T 150 — body and jacket tested independently on degasser vessels
• Vacuum leak test: helium leak detection on all vessels to verify seal integrity under full vacuum conditions
• Interior surface polishing verification: Ra measurements at documented grid points, all readings ≤ 0.4 μm
• Final dimensional survey and nozzle orientation check against certified drawings

Delivery was coordinated directly with Wacker’s Zhangjiagang site team. The proximity between Lmart’s workshop and Wacker’s plant — both located in Zhangjiagang — allowed overland transport by flatbed truck, eliminating the cost and risk of long-distance shipping for these oversized vessels. The DN3000 mixing vessels required wide-load permits and escort vehicles for the short road transfer.

Results and Business Impact

All five vessels were delivered on schedule, passed Wacker’s incoming inspection at the plant site, and entered service in the silicone polymer production line without modification or rework. Interior surface finish measurements confirmed Ra ≤ 0.4 μm across all polished surfaces, meeting Wacker’s process cleanliness requirements for polymer contact equipment.

This project represents the second major equipment package Lmart has delivered to Wacker’s China operations, following the earlier 18-unit duplex stainless steel heat exchanger order. The progression from heat exchangers to large process vessels — with more demanding surface finish and vacuum design requirements — reflects Wacker’s growing confidence in Lmart’s capability to handle increasingly complex fabrication scopes.

For Lmart, Wacker represents a strategically important reference in the European specialty chemical sector. Wacker’s global reputation and rigorous quality standards make this reference directly transferable to other multinational chemical companies evaluating local Chinese manufacturers for process equipment procurement.

Customer Voice

Wacker Chemie placed a second major equipment order with Lmart after the successful completion of the duplex heat exchanger project — expanding the scope from heat transfer equipment to large-volume process vessels with more demanding surface finish specifications.

“The interior polishing quality and the vacuum leak test results met our global standards. Fabrication quality was consistent across all five units.”

— Wacker Chemie project engineering team (paraphrased from inspection feedback)

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