Manufacturing Process for Inner Wall Weld Overlay of S31603 Gasifier Shells

Literature Overview

This 2017 paper by Wang Puxuan from Shanxi Fengxi Chemical Equipment Co., Ltd. details the manufacturing process for inner wall weld overlay of S31603 (equivalent to 316L) stainless steel on gasifier shells. Gasifiers used in coal-to-chemical conversion processes operate under extreme conditions of high temperature, high pressure, and highly corrosive environments containing hydrogen sulfide, water vapor, and alkali metals. The selection of S31603 as the overlay material reflects the need for superior corrosion resistance compared to standard 304 stainless steel, particularly in chloride-containing environments and reducing atmospheres.

Core Technical Content

The paper addresses the manufacturing challenges of applying a corrosion-resistant overlay layer to the interior surface of large-diameter gasifier shells. These shells typically have diameters of 2.5–4.0 m and wall thicknesses of 30–50 mm, presenting significant challenges for achieving uniform overlay coverage and maintaining dimensional accuracy.

Material System and Welding Consumables

The overlay material system employs S31603 stainless steel as the primary corrosion-resistant layer, with careful attention to the transition zone between the carbon steel base and the stainless steel overlay. The consumable selection is critical:

The use of a 309L transition layer is essential to prevent chromium carbide precipitation at the fusion boundary, which could lead to intergranular corrosion and reduced mechanical properties. The 309L composition, with its high nickel and chromium content, provides a dilution buffer that ensures the final overlay composition remains within acceptable limits even with moderate base metal dilution.

Process Parameters and Welding Sequence

The paper describes a multi-pass welding procedure with the following key parameters:

• Welding method: Submerged arc welding (SAW) for the transition and overlay layers, supplemented by gas metal arc welding (GMAW) for root preparation and repair
• Current range: 400–550 A for SAW, 120–180 A for GMAW
• Voltage: 28–35 V for SAW, 20–25 V for GMAW
• Travel speed: 250–350 mm/min for SAW
• Preheat temperature: 100–150 °C for carbon steel base, maintained throughout welding
• Interpass temperature: Maximum 200 °C
• Post-weld heat treatment: Stress relief at 580–620 °C, 2 h per 25 mm of thickness

The welding sequence for the inner wall overlay follows a systematic approach:

1. Surface preparation: Complete removal of scale, rust, and mill oxide by grinding to bare metal, followed by solvent cleaning within 4 hours of welding
2. Root pass: Single-pass GMAW or GTAW to establish a clean fusion boundary
3. Transition layer: 2–3 passes of 309L material, each with a thickness of 3–4 mm
4. Overlay layer: 3–5 passes of 316L material, achieving a total overlay thickness of 8–12 mm
5. Surface finishing: Grinding to achieve surface roughness Ra ≤ 3.2 μm for corrosion performance

Quality Control Measures

The paper emphasizes several critical quality control checkpoints:

Key Technical Challenges

The manufacturing of inner wall overlay for gasifier shells presents several unique challenges that the paper addresses:

Challenge 1: Access and positioning

Working on the interior surface of a large-diameter shell requires specialized fixtures and welding positioners. The paper describes the use of a rotary positioner with internal welding access through manholes, requiring careful planning of the welding sequence to minimize the number of access points needed.

Challenge 2: Thermal distortion control

The overlay welding of large areas on thin-walled shells can cause significant barrel distortion. The paper recommends a symmetric welding sequence, welding in alternating quadrants to maintain thermal balance. The use of low-heat-input parameters and controlled interpass temperatures is critical to limiting distortion to within ±2 mm per meter.

Challenge 3: Dilution control

Achieving the required overlay composition requires careful management of base metal dilution. The paper reports dilution rates of 8–15% for the first overlay pass and 3–8% for subsequent passes. The 309L transition layer is specifically designed to accommodate higher dilution rates while maintaining acceptable corrosion properties.

Challenge 4: Hydrogen-induced cracking prevention

The combination of high-strength carbon steel base material and stainless steel overlay creates a susceptibility to hydrogen-induced cracking at the fusion boundary. The paper recommends strict control of hydrogen sources through the use of low-hydrogen fluxes, thorough flux drying, and post-weld baking at 150–200 °C for 1–2 hours before stress relief.

Engineering Practice Integration

The manufacturing approach described in this paper aligns with industry best practices for gasifier shell overlay as documented in API 934 and relevant Chinese standards (NB/T 47014). The paper's emphasis on the transition layer is particularly important, as many field failures of gasifier overlays have been traced to inadequate transition zone design.

The overlay thickness of 8–12 mm specified in the paper is consistent with typical design requirements for gasifier applications, where 6–10 mm is the minimum specified thickness per API 934. The additional thickness provides a margin for future grinding and repair during the service life of the equipment.

The intergranular corrosion testing requirement is particularly relevant for 316L overlay in gasifier applications, where the reducing atmosphere can promote chromium carbide precipitation if the overlay composition is not properly controlled. The paper's specification of ASTM A262 Practice E testing at 800 °C for 10 hours provides a rigorous verification of the overlay's resistance to sensitization.

Study Reflections

This paper provides a valuable case study of gasifier shell overlay manufacturing in the Chinese coal-to-chemical industry. The systematic approach to process planning, quality control, and defect prevention reflects a mature understanding of overlay welding technology. The paper's emphasis on the transition layer design and hydrogen control is particularly noteworthy, as these are common sources of field failures that are often overlooked in less experienced manufacturing operations. For engineers involved in gasifier equipment fabrication, this paper offers practical guidance on process parameter selection and quality assurance procedures that can be directly applied to similar projects.