How can we prevent defects from occurring in stainless steel degreased seamless pipes during

How can we prevent defects from occurring in stainless steel degreased seamless pipes during the degreasing process? 

To avoid the degreasing defects of stainless steel seamless tubes, it is necessary to start from four aspects: process parameters, reagent selection, equipment compatibility, and process monitoring. The core is to balance the cleaning efficiency and material protection. The specific measures are as follows:

1. Precise control of degreasing process parameters

Optimization of sandblasting degreasing

The abrasive material is selected as 0.05 - 0.2mm glass beads or plastic sand, instead of alumina abrasive. The sandblasting pressure is ≤ 0.4MPa, and the spraying angle is 45° - 60°. To avoid surface scratches (depth <0.1mm) and excessive roughness (Ra controlled within 1.6 - 2.5μm). 

Ultrasound degreasing parameter limitations

Power is controlled within 500-800W (frequency 30-40kHz), degreasing time ≤ 15 minutes. Combined with 10L/min flow rate for spray rinsing, it reduces surface pitting caused by cavitation effect. 

II. Selection of Degreasing Agents and Concentration Control

Improvement of Alkaline Degreasing Agents

Reduce the NaOH concentration to 8% - 12%, add 3% - 5% silicate corrosion inhibitors, control the temperature at 50 - 60℃, maintain the pH at 9 - 11, and avoid intergranular chromium deficiency (intergranular corrosion test corrosion rate <0.03mm/year). 

Solvent degreasing alternative solution

Use isopropyl alcohol (purity ≥ 99.5%) or weakly alkaline water-based degreasing agent (containing EO-PO block copolymer), with residual content controlled to be less than 5mg/m², to reduce the risk of chemical corrosion. 

III. Protective Design for Mechanical Degreasing Equipment

Roller Degreasing Anti-Deformation

For thin-walled tubes (with a wall thickness of less than 2mm), the rotational speed should be ≤ 10 rpm. Polyurethane pads should be installed on the inner wall of the roller, and the ellipticity should be controlled within 0.3% to prevent dimensional deviations caused by mechanical collisions. 

Limitation of high-pressure water degreasing pressure

Using a rotating nozzle for uniform spraying, the pressure should be ≤ 40 MPa. The nozzle should be 10 to 15 cm away from the workpiece to prevent local impact from causing surface depressions (depth <0.05 mm). 

IV. Process Monitoring and Post-Treatment Coordination

De-greasing Time Control

Within 30 minutes after de-greasing, use multi-stage spraying with deionized water (conductivity <10 μS/cm) to remove residual chemicals and prevent local accumulation of alkaline substances that could cause corrosion. 

Material-specific protective measures

304/316L austenitic steel: Add 0.5% - 1% molybdate to the degreasing agent to prevent intergranular corrosion;

430 ferritic steel: Use a 40 - 50℃ neutral degreasing agent to avoid surface oxidation;

Dual-phase stainless steel: With an ultrasonic power of ≤ 600W, prevent hydrogen embrittlement (tensile test elongation rate ≥ 30%). 

Key Defect Warning and Countermeasures

Surface Scratches

Causes: Hard abrasive material / Excessive pressure

Prevention Measures: Use glass beads + ≤ 0.4 MPa sandblasting

Detection Indicators: Observe scratch depth with a microscope <0.1 mm 

Intergranular corrosion

Cause: Excessive concentration of alkaline agent

Prevention measures: Reduce NaOH to 8% - 12% + silicate corrosion inhibitor

Testing indicators: Corrosion rate according to ASTM A262 E method <0.02mm/year 

Dimensional deformation

Causes: Rotating speed of the drum is too fast

Prevention measures: Thin-walled pipe rotating speed ≤ 10 rpm + elastic support

Detection indicators: Ellipticity ≤ 0.3%, Straightness ≤ 1mm/m 

Chemical burn

Causes: Residual degreasing agent not cleaned

Prevention and control measures: Rinse with deionized water within 30 minutes after degreasing

Test indicators: No blue spot in the blue spot test 

Summary

By precisely controlling the hardness of the abrasive, the concentration of the chemical agent, and the mechanical force parameters, and adjusting the process in combination with the material properties, the defect rate of degreasing can be reduced to below 1% (such as the incidence of surface scratches being less than 0.5%, and the detection rate of intergranular corrosion being less than 0.3%), ensuring the corrosion resistance of the seamless pipe (salt spray test lasting over 500 hours without rust) and meeting the dimensional accuracy requirements.