Why Housing Material Matters
The pump housing is your first line of defense against the fluid being transferred. In aggressive chemical environments, a weak housing leads to corrosion, leaks, and premature failure. In benign applications, an oversized material selection increases cost without benefit. NAPCO offers both stainless steel and ductile iron housings precisely because no single material is optimal for all applications.
The material choice affects four critical factors: initial cost, chemical compatibility, service life expectancy, and maintenance requirements. Understanding these tradeoffs ensures you select the right pump the first time.
Stainless Steel Pumps: Superior Corrosion Resistance
NAPCO stainless steel pumps are manufactured from 316L stainless steel, offering exceptional resistance to a wide range of corrosive fluids. The 316L designation includes molybdenum, which provides enhanced resistance to chloride corrosion compared to standard 304 stainless.
Applications for Stainless Steel
Stainless steel pumps are the global standard for emulsion explosives transfer. Ammonium nitrate, the primary oxidizer in bulk emulsions, is inherently corrosive to carbon steel and cast iron. Mining operations worldwide rely on PA300S and PA200S stainless pumps to safely transfer emulsion explosives from manufacturing plants to mobile loading trucks and remote mine sites.
Chemical processing plants use stainless housings for acids, bases, oxidizers, and solvents that would attack ductile iron within months. Food-grade applications also benefit from the hygienic properties of stainless steel, though NAPCO gear pumps are more common in heavy-duty industrial chemical work than in food manufacturing.
Stainless Steel Shaft
NAPCO stainless steel pumps feature stainless steel shafts as well, ensuring the entire wetted path resists corrosion. This is essential in emulsion explosives applications where even microscopic pitting on a shaft can lead to leakage and seal failure over extended service life.
Cost Considerations
Stainless steel pumps carry a higher initial cost than ductile iron equivalents. However, when operating in corrosive environments, the extended service life and reduced maintenance costs often justify the premium within the first operating year. A stainless pump lasting eight years costs less per year than a ductile iron pump that must be replaced every two to three years in the same application.
Ductile Iron Pumps: Cost-Effective Strength
Ductile iron is an iron alloy containing graphite in nodular form, providing superior strength and impact resistance compared to gray cast iron. NAPCO ductile iron pumps are engineered for heavy-duty industrial use, with excellent performance in adhesives, sealants, petroleum products, and general industrial fluids.
Alloy Steel Shaft
Ductile iron housings are paired with alloy steel shafts, which provide good strength and wear resistance in non-corrosive applications. This combination balances durability with cost-effectiveness for industries where corrosion is not a concern.
The Adhesive Industry Standard
The PA300C ductile iron pump has become the standard in the adhesive and sealant industry. Boise Cascade, a major wood products manufacturer, relies on PA300C pumps for continuous-duty adhesive transfer. Because adhesives are not corrosive to iron and ductile iron provides excellent strength for handling viscous fluids, the economics favor ductile iron in this market segment.
The same applies to petroleum transfer applications. PA300C and PA200C pumps are proven workhorses for fuel transfer, crude oil handling, and petroleum product circulation where corrosion is minimal and cost control is important.
Maintenance Advantage
Ductile iron pumps are rugged and forgiving. In non-corrosive applications, they require minimal maintenance and demonstrate excellent reliability. When service is needed, NAPCO factory-matched repair kits (PK300C, PK200C) enable field rebuilds without factory return.
Stainless Steel vs. Ductile Iron: Comparison Table
| Property | Stainless Steel (316L) | Ductile Iron |
|---|---|---|
| Corrosion Resistance | Excellent (most acids, bases, oxidizers) | Fair (non-corrosive fluids only) |
| Chemical Compatibility | Wide range (includes ammonium nitrate) | Limited (oils, adhesives, fuels) |
| Initial Cost | Higher (25–40% premium) | Lower (baseline cost) |
| Weight (3" pump) | 173 lbs | 173 lbs |
| Weight (2" pump) | 114 lbs | 114 lbs |
| Tensile Strength | Good (corrosion resistance priority) | Excellent (higher tensile strength) |
| Service Life (corrosive) | 8–10+ years | 2–3 years (if corrosive) |
| Service Life (non-corrosive) | 10+ years (overkill cost) | 10+ years (optimal cost) |
Performance specifications (flow rate, pressure, displacement) are identical within the same pump size class, regardless of housing material.
Industry-Specific Decision Guide
Use this guide to determine which material is right for your industry and application:
Explosives & Mining
Recommended: Stainless Steel (PA300S, PA200S)
Bulk emulsion explosives contain ammonium nitrate, which corrodes carbon steel and cast iron rapidly. Stainless steel is the global standard and essential for safe, reliable operation. Ductile iron will fail within months in this application.
Adhesives & Sealants
Recommended: Ductile Iron (PA300C, PA200C)
Hot melt and water-based adhesives are non-corrosive. Ductile iron provides the strength needed for viscous fluids at a fraction of stainless steel cost. This is the most cost-effective choice for adhesive transfer.
Chemical Processing
Recommended: Stainless Steel (PA300S, PA200S)
Acids, bases, oxidizers, and specialty chemicals attack iron rapidly. Stainless steel is essential for reliable performance in chemical plants. The investment pays for itself through extended service life and reduced downtime.
Petroleum, Fuel & Lubrication
Recommended: Ductile Iron (PA300C, PA200C)
Oil, fuel, and lubricants are non-corrosive to iron. Ductile iron offers proven performance and superior strength for high-viscosity transfer at lower cost. Standard choice for the petroleum industry.
Performance Equivalence Within Size Class
A critical point: NAPCO stainless steel and ductile iron pumps of the same size have identical performance specifications. A PA300S (stainless) and PA300C (ductile iron) pump deliver the same flow rate, pressure rating, and displacement. The choice is purely about chemical compatibility and total cost of ownership in your specific environment.
This means you can select based on application requirements without sacrificing performance. If your fluid is corrosive, choose stainless for reliability. If your fluid is benign, choose ductile iron for cost savings. Either way, you get the same throughput and the same NAPCO quality.
Related NAPCO Products
Not Sure Which Material Is Right?
NAPCO application engineers can help. Provide your fluid type, operating environment, and flow requirements, and we'll recommend the optimal pump configuration.
Contact NAPCO Engineering