Zhuojin Pipe Fitting Co., LtdTechnology of Inner Wall Overlay Welding for Flange Forging Blanks
Literature Overview
The paper by Chen Sunyi (2005), published in Hot Working Technology (Vol. 34, No. 5, pp. 67-68), addresses a specific manufacturing challenge in the production of composite flanges with stainless steel overlay weld layers on the inner wall of forged blanks. Developed at Sinopec Maoming Petrochemical Machinery Factory, this work presents practical solutions to distortion control and cost optimization in the manufacturing of lined flanges for chemical and petrochemical applications.
Problem Statement
The manufacturing of composite flanges with stainless steel inner wall overlay involves two critical challenges:
- Welding distortion: The asymmetric heat input from inner wall overlay welding causes significant barrel distortion, warping, and diameter changes that compromise dimensional accuracy and subsequent machining.
- Ultrasonic testing requirements: The forging blank must meet ultrasonic inspection (UT) standards for soundness, which constrains the blank geometry and manufacturing approach.
Blank Design Alternatives
The study proposes two alternative blank designs compared to the conventional ring blank:
Blank Geometry Comparison
| Blank Type | Description | Cost Level | Distortion Risk | UT Compliance |
|---|---|---|---|---|
| Conventional ring blank | Full ring with bore | High | High | Good |
| Contour blank (仿形毛坯) | Profile-matched to final flange shape | Moderate | Moderate | Good |
| Column-neck blank (柱颈毛坯) | Simplified geometry with reduced material | Low | Low | Acceptable |
The contour blank is shaped to approximate the final flange profile, reducing the amount of asymmetric material and therefore reducing the driving force for distortion. The column-neck blank offers the lowest material cost but requires careful process control to ensure adequate overlay coverage.
Distortion Control Measures
For the contour blank approach, the study identifies five measures:
Pre-Welding Preventive Measures (Four Methods)
| Method | Description | Advantage | Limitation |
|---|---|---|---|
| 1. Backing plate support | Rigid backing constrains inner wall movement | Simple and effective | Requires precise fit-up |
| 2. Symmetric dummy welds | Welds on outer wall balance thermal asymmetry | Direct thermal compensation | Additional welding time |
| 3. Sequential welding pattern | Controlled sequence from high to low stress zones | Reduces cumulative distortion | Complex programming |
| 4. Pre-deformation | Intentional deformation opposite to expected distortion | Cost-effective | Requires accurate prediction |
Post-Welding Corrective Measure
| Method | Description | Application |
|---|---|---|
| Thermal correction | Localized heating to induce corrective deformation | Final dimensional adjustment |
Welding Process Parameters
For stainless steel inner wall overlay welding of flange components, typical process parameters include:
| Parameter | Range | Rationale |
|---|---|---|
| Welding method | GTAW or SAW (with backing) | Penetration control and quality |
| Wire diameter | 1.0-1.6 mm | Deposition rate vs. heat input balance |
| Current | 150-250 A (GTAW) | Adequate penetration without excessive HAZ |
| Travel speed | 5-15 cm/min | Layer thickness control (2-3 mm per pass) |
| Interpass temperature | <200°C | Prevent sensitization and distortion accumulation |
| Backing gas | Argon | Prevent oxidation of root pass |
| Number of passes | 3-5 | Achieve 6-10 mm overlay thickness |
Engineering Practice Integration
The practical implementation of this technology requires consideration of:
- Material compatibility: The base forging material (typically carbon steel or low-alloy steel per ASTM A105 or ASME SA-105) must be compatible with the stainless steel overlay (typically 304, 316, or 321 per ASTM A403). Intermetallic compound formation at the interface must be controlled through dilution management.
- Dimensional tolerance control: ASME B16.5 or EN 1092-1 dimensional requirements must be maintained after overlay welding, including bore diameter, face flatness, and bolt hole position.
- Corrosion resistance verification: The overlay must provide continuous, crack-free protection. Visual inspection, magnetic particle testing (MT), and penetration testing (PT) are standard verification methods.
- Residual stress management: Post-weld stress relief (PWSR) at 620-675°C for carbon steel base with stainless overlay may be required, but must be carefully controlled to avoid sensitization of the stainless overlay.
FMEA Analysis of Distortion Failure Modes
| Failure Mode | Cause | Effect | Detection | Prevention |
|---|---|---|---|---|
| Barrel distortion | Asymmetric heat input | Bore diameter increase | CMM measurement | Symmetric welding sequence |
| Face warping | Uneven cooling rate | Flatness deviation | Straight edge check | Backing plate support |
| Bolt hole displacement | Localized distortion | Assembly interference | Hole gauge check | Pre-deformation compensation |
| Overlay cracking | High residual stress | Loss of corrosion protection | MT/PT inspection | Controlled interpass temperature |
| Excessive dilution | High heat input | Reduced corrosion resistance | Metallographic examination | Lower current, higher speed |
Summary
This study provides practical, cost-effective solutions for the inner wall overlay welding of flange forging blanks, addressing both distortion control and manufacturing economy. The proposed contour and column-neck blank designs, combined with systematic distortion prevention and correction measures, represent a mature engineering approach that balances quality requirements with production cost. The methodology is directly applicable to the manufacturing of lined flanges for petrochemical, chemical, and process industries where stainless steel corrosion resistance is required in specific service areas while maintaining the strength and cost-effectiveness of carbon steel or low-alloy steel base materials.