Process Technology for Internal Wall Cladding of Flange Forging

Literature Overview

This study note addresses a 2005 publication from Maoming Petrochemical Machinery Works, China Petrochemical Corporation, concerning the thermal processing technology for internal wall cladding of flange forgings. The document falls within the broader domain of hot working processes applied to weld overlay operations on large-diameter flange components used in petrochemical pressure equipment. Flange forgings are critical structural elements in high-pressure piping systems, and the internal bore cladding provides corrosion resistance while maintaining the mechanical integrity of the carbon steel or low-alloy steel base material.

Core Technical Approach

The key innovation described in this work centers on the application of hot working processes to prepare and facilitate the cladding operation on the internal wall of flange forgings. Traditional cladding methods applied to flange internals often face challenges related to geometry constraints, heat input control, and achieving full penetration bonding between the overlay layer and the base metal. The hot working approach involves pre-heating and controlled thermal cycling to reduce residual stresses and improve weldability during the overlay process.

Process Parameters and Thermal Treatment

Parameter	Typical Range	Purpose
Pre-heat temperature	250–350 °C	Reduce hydrogen cracking susceptibility
Interpass temperature	200–300 °C	Control cooling rate and microstructure
Post-weld heat treatment	600–650 °C for 2–4 h	Stress relief and microstructure homogenization
Cladding thickness	3–6 mm per pass	Ensure full bonding without dilution
Base material	16Mn, 15CrMo, or 20# steel	Structural strength
Overlay material	304, 316, or 321 stainless steel	Corrosion resistance

Engineering Practice Integration

In the context of GB/T 150 and NB/T 47002 compliance, the internal wall cladding of flange forgings requires strict control over the bond strength between the overlay layer and the base material. The hot working process described in this study addresses the challenge of achieving consistent bonding on curved internal surfaces where access for welding is geometrically constrained. The use of hot rolling or hot forging pre-treatment before cladding helps to refine the grain structure of the base material, thereby improving the metallurgical compatibility at the interface.

Defect Analysis and Countermeasures

Defect Type	Root Cause	Countermeasure
Incomplete bonding	Insufficient pre-heat or excessive cooling rate	Increase pre-heat to 300 °C, reduce interpass cooling
Cracking in overlay	Hydrogen embrittlement from high heat input	Use low-hydrogen consumables, control interpass temperature
Surface porosity	Contamination of cladding surface	Thorough cleaning and flux coverage
Dilution exceeding limits	Excessive penetration into base metal	Reduce welding current, increase travel speed

Study Insights and Reflections

The significance of this work lies in its practical orientation toward resolving a persistent manufacturing challenge in petrochemical equipment fabrication. The hot working approach demonstrates that the preparation of the base material surface and thermal conditioning of the forging are as critical as the welding parameters themselves. From a quality assurance perspective, the bond strength test results (typically requiring a minimum of 30 MPa peel strength per NB/T 47014) must be verified through destructive testing of coupon samples taken from representative locations. This study reinforces the principle that successful cladding on complex geometries requires a holistic approach integrating metallurgical preparation, welding process control, and post-weld treatment within a single quality management framework. The methodology described here has direct applicability to modern hydrogenation reactor flanges and high-pressure separator internals where corrosion-resistant overlays are mandatory.