How to Choose Wetted Materials for Chemical Liquid Filling Machines: Evaluating Corrosion Resistance and Seal Compatibility

For chemical liquid filling machines, wetted materials cannot be selected simply by asking “304 or 316L?” First identify the medium’s composition, concentration, temperature, and cleaning conditions, then assess the suitability of the metals, plastics, and seals separately. Corrosion resistance of the metal does not mean the entire liquid path is compatible, and a seal that does not dissolve is not necessarily capable of maintaining a seal over the long term.

After a formula change or an increase in cleaning temperature, the same machine may develop issues such as filling valve leakage, hardened hoses, or particles in the liquid. During selection, treat storage, transfer, metering, filling, and cleaning as one complete wetted path rather than confirming only the tank material.

Document the medium and operating conditions before consulting corrosion resistance charts

“Acidic liquid,” “alkaline solution,” or pH alone is not enough to select materials reliably. Solutions with similar pH values may affect materials differently because of variations in chloride ions, oxidizing agents, or solvent components. Compatibility conclusions for a single ingredient cannot be applied directly to a mixture either.

• Medium information: List the main components, concentration range, impurities, and any possible residues from the previous batch. If the formula is confidential, provide component categories sufficient to assess compatibility.
• Operating limits: Record normal and maximum temperatures, operating pressure and fluctuations, and the duration of continuous contact and shutdown soaking. Do not provide only room-temperature filling conditions.
• Cleaning conditions: Specify the concentration, temperature, and contact time of cleaning agents and disinfectants, as well as the rinsing sequence. Pay particular attention to alternating acid and alkali cleaning and oxidizing cleaning.

Safety data sheets can serve as a starting point, but may not include the complete formula. When using material compatibility charts for preliminary screening, check the test temperature, concentration, and applicable grade. A “resistant” rating without key test conditions should not be used directly as a basis for procurement.

What are the respective limits of metals and engineering plastics?

If the operating range of a base material is insufficient, consider evaluating a specialized alloy or a lined construction. However, selecting a higher stainless-steel grade as a precaution is not a reliable solution. Welds, valve-seat crevices, threaded connections, and stagnant areas often require separate review. Even materials with the same name may perform differently in terms of corrosion resistance after processing and assembly.

Seal compatibility: assess both chemical changes and functional performance

Seal failure does not always present as visible cracking. Swelling may increase resistance to valve stem movement; extraction or shrinkage may reduce the sealing compression; and hardening may impair the seal’s ability to compensate. Seal selection must therefore assess not only resistance to the medium, but also whether the seal can maintain its function under the specified temperature, differential pressure, and actuation frequency.

• EPDM: Commonly used in some water-based, acid, alkali, and hot-water applications, but this should not be taken to mean it is suitable for mineral oils or hydrocarbon solvents.
• FKM: Suitable for some oil and solvent environments, but should not be described simply as “universally corrosion-resistant.” Conditions involving ketones, amines, and hot alkalis require specific verification.
• PTFE seals: Offer broad chemical resistance, but have limited elastic recovery. Their suitability should be evaluated in relation to the valve seat structure, preload method, and wear conditions.

“Fluoroelastomer” and “silicone” refer only to material categories. Specific formulations, hardness, and curing systems can also affect performance. Require suppliers to provide traceable seal grades, and include the hose inner layer, pump diaphragm, metering component seals, and filling nozzle valve seat in the review to avoid checking only the primary seal.

How can testing provide a sound basis for decisions when information is limited?

Start by screening samples made from the actual medium and actual material grades, covering production contact, shutdown soaking, and the cleaning process separately. Test mixtures using the complete formula. The test duration and temperature should represent actual conditions; short-term immersion at room temperature cannot replace long-term or high-temperature evaluation.

For metal samples, inspect not only surface and mass changes but also localized pitting; assess welded areas when necessary. For elastomers, compare volume, mass, hardness, appearance, and recovery. “No visible change” is not sufficient to determine acceptance. Acceptance limits should be agreed in advance based on material data and component function.

After screening, test actual components under static pressure-holding and dynamic operating conditions, monitoring leakage, actuation resistance, metering stability, and wear. Testing with hazardous media requires appropriate protective, ventilation, and containment measures. Do not test unknown media compatibility by running a complete machine directly with the material on the production floor.

Document material selection decisions in the equipment specification

The technical agreement should list each wetted component, material grade, seal model, permitted operating conditions, and restrictions on replacements, and require the supplier to explain the basis for material selection. For equipment handling multiple formulas on the same line, select materials compatible with all materials and cleaning procedures. If there is no common compatibility range, consider a separate liquid path or replaceable components.

When evaluating additional equipment, the DGP-18 fully automatic 18-head electronic quantitative filling machine can be included among the candidates for review, but its model and metering method do not demonstrate corrosion resistance. Request details of its wetted materials, seal configuration, and operating-condition suitability before deciding whether it is appropriate for the target medium.

Recheck compatibility after changing the formula, seal supplier, or cleaning procedure. If rust spots, blistering of the lining, tacky seals, or persistent leakage occur on site, stop operating the affected components and investigate the cause. Do not rely solely on tightening fittings or replacing seals with similar ones to keep production running.