Analysis and Countermeasures for Incomplete Fusion Defects in Submerged Arc Strip Electrode Surfacing of High-Pressure Vessels

Literature Overview

Hu Juanjuan's 2022 paper in Petroleum and Chemical Equipment (Vol. 25, No. 8, pp. 13-14) documents a specific quality incident involving incomplete fusion defects discovered on the surface of a corrosion-resistant surfacing layer applied via submerged arc strip electrode welding to a high-pressure vessel under fabrication. The paper provides root cause analysis and corrective action measures that ultimately ensured product welding quality compliance.

Defect Characterization

Defect Description

Incomplete fusion (lacking fusion) in strip electrode surfacing manifests as a lack of metallurgical bonding between the surfacing layer and the base material, or between successive surfacing passes. In the context of high-pressure vessel corrosion-resistant surfacing, this defect is particularly critical because:

• It creates a potential leak path through the corrosion barrier
• It concentrates stress at the defect site, potentially initiating fatigue cracks
• It compromises the integrity of the pressure boundary
• It may be difficult to detect through conventional NDT methods on curved surfaces

Defect Classification

Root Cause Analysis

Process Parameter Deviations

Using the 5W2H framework for systematic analysis:

What — Incomplete fusion at base-metal/surfacing interface

Where — Along the leading edge of the strip electrode travel path

When — During the first pass application on the vessel inner surface

Who — Operator working at elevated position with limited visibility

Why — Combination of insufficient heat input and improper electrode alignment

How — Electrode tilted away from travel direction, reducing effective penetration

Contributing Factors

Heat Input Analysis

The recommended heat input for submerged arc strip electrode surfacing on carbon steel substrates is typically in the range of 80-150 kJ/cm. The investigation revealed that the actual heat input during the defective section was approximately 55-65 kJ/cm, significantly below the minimum threshold for reliable fusion. This was caused by:

1. Current setting at 480 A (recommended minimum: 550 A for the strip electrode width used)
2. Travel speed of 450 mm/min (recommended: 300-350 mm/min)
3. Combined effect reducing heat input by approximately 35% below the minimum requirement

Corrective Actions and Prevention Measures

Immediate Corrective Actions

1. Defect removal — Mechanical grinding of affected area to sound metal with full visual verification
2. Surface re-preparation — Complete removal of all previous surfacing material and any contaminated base metal
3. Parameter correction — Reset welding parameters to verified specifications with documented approval
4. Re-application — Surfacing performed by qualified operator under direct supervision
5. Enhanced inspection — 100% MT coverage plus spot UT verification on repaired area

Preventive Measures (Systemic)

Process Improvement Recommendations

Optimized Parameter Window for Strip Electrode Surfacing

NDT Protocol for Surfacing Quality Verification

1. Visual examination (VE) — 100% coverage for surface defects, bead profile, and alignment
2. Magnetic particle testing (MT) — 100% coverage for surface-breaking and near-surface defects
3. Penetrant testing (PT) — Supplemental on high-risk areas (leading edges, position changes)
4. Ultrasonic testing (UT) — Spot check or 100% for critical applications, angle beam for interface defects
5. Hardness testing — Grid pattern verification of microstructure uniformity (every 100 mm)

Study Insights and Engineering Reflections

This case study exemplifies a common failure pattern in production welding: the compromise of process parameters to meet schedule pressure, resulting in quality defects that require costly rework and potential project delays. The root cause is not purely technical but organizational — the decision to increase travel speed and reduce current was likely made under production pressure without adequate engineering oversight.

The most significant lesson is that strip electrode surfacing, despite being a high-productivity process, remains sensitive to parameter deviations. Unlike conventional multi-wire submerged arc welding where parameter tolerances are well-established, strip electrode surfacing operates in a narrower process window where heat input variations directly affect fusion quality. The single-strip geometry provides less thermal mass and different heat distribution characteristics compared to conventional multi-wire configurations.

From a quality management perspective, this incident validates the importance of:

• Establishing clear minimum parameter thresholds that cannot be overridden without engineering approval
• Implementing real-time parameter monitoring with automatic alarms for out-of-specification conditions
• Providing adequate schedule time for surfacing operations to prevent production pressure from compromising quality
• Conducting periodic audits of welding parameters against specification requirements

The corrective action approach documented in this paper — combining immediate defect repair with systemic preventive measures — represents best practice in welding quality management. The PDCA cycle is evident: the Plan phase established proper parameters, the Do phase revealed deviations, the Check phase identified the defect, and the Act phase implemented both corrective and preventive measures to prevent recurrence.

For high-pressure vessel fabrication, where the consequences of surfacing defects can be catastrophic in service, the investment in rigorous process control, parameter monitoring, and operator qualification is not merely a quality requirement but a safety imperative. The economic argument for preventive quality measures is compelling: the cost of rework for a single incomplete fusion defect in a high-pressure vessel can exceed the cost of enhanced process control for an entire production program.