Durco Mark III Group 2 Replacement Casing — 100% Bolt-On Interchange
The Flowserve Durco Mark III Group 2 (medium-frame) casing operates at the hydraulic heart of some of the most demanding chemical process loops in North American refineries, pharmaceutical batch reactors, and chlor-alkali plants. These casings endure continuous exposure to corrosive media at elevated temperatures and pressures — and when the volute wall thickness erodes below the corrosion allowance, the risk shifts from performance degradation to catastrophic containment loss. A properly engineered replacement must address three interdependent requirements: dimensional fidelity (bolt-circle geometry, nozzle centerlines, and volute tongue clearance so the pump curve stays on its BEP), metallurgical integrity (alloy chemistry verified to ASTM specification with full heat traceability), and structural robustness (adequate wall thickness to survive the design corrosion allowance between turnaround intervals). This guide covers the failure mechanisms that drive Group 2 casing replacements, the material selection logic for different process chemistries, and the quality verification standards you should require before accepting a replacement casing into your maintenance inventory.
Full Material Coverage for Severe Corrosion Control
We specialize in pouring high-alloy castings to handle the most aggressive chemical applications. The following wet-end materials are fully available for our Group 2 casings:
⚠️ Quality & Compliance Assurance
All pumps and components from ANSI Pumps Pro are manufactured to ASME B73.1 dimensional specifications. Each shipment includes certified Material Test Reports (MTRs), CMM dimensional inspection reports, and hydrostatic test certificates (1.5× MAWP). 100% dimensional interchangeability guaranteed. Full material traceability from heat number to your receiving dock.
Material Selection Logic for Group 2 Casing Replacements
- CF8M (ASTM A743 CF8M, PREN ≥ 24): Adequate for general chemical transfer at near-neutral pH and low chloride levels (< 200 ppm). Limitation: Susceptible to pitting and crevice corrosion once chloride concentrations or operating temperatures rise. Best suited for non-critical water treatment, dilute organics, and mild chemical services where corrosion rates are predictable.
- CD4MCuN (ASTM A890 Gr. 1B, PREN ≥ 35): The workhorse for chloride-bearing environments — seawater cooling loops, brine services, and brackish process water. Delivers roughly double the yield strength of CF8M while providing substantially better resistance to chloride pitting. Selection trigger: When your process fluid contains more than 500 ppm chlorides at operating temperature.
- Alloy 20 / CN7M (ASTM A744 CN7M, PREN ≈ 28): Specifically developed for sulfuric acid service across the 10–80% concentration range at temperatures up to 50°C. The 3–4% copper addition provides a unique resistance mechanism against reducing sulfuric acid attack that standard stainless grades lack. Selection trigger: Medium-concentration H₂SO₄, phosphoric acid, or mixed-acid streams where sulfates dominate.
- Hastelloy C-276 (ASTM A494 CW12MW, PREN ≥ 64): The premium solution for mixed oxidizing-reducing acid environments, wet chlorine gas, and hot contaminated mineral acids. Its exceptionally high nickel and molybdenum content provides near-immunity to localized attack in the most severe chemical reactor and scrubber applications. Selection trigger: When process conditions combine low pH, high chlorides, and oxidizing species simultaneously.
- Titanium Grade 2 (ASTM B367 Gr. C-3, PREN ≥ 30): Uniquely resistant to oxidizing chloride environments — hypochlorites, wet chlorine, and nitric acid across all concentrations. Titanium forms an instantly self-healing passive TiO₂ film that is virtually immune to chloride pitting. Selection trigger: Oxidizing chloride services where even Hastelloy shows measurable corrosion rates.
Technical Specifications & Pressure Ratings
| Specification | Detail |
|---|---|
| Pump Compatibility | Flowserve Durco Mark III Group 2 (Medium Frame) |
| Common ANSI Sizes | 2×3-8, 3×4-8, 3×4-10, 4×6-10, 6×8-13 |
| Flange Standard | ASME B16.5 Class 150 / Class 300 |
| Max Working Pressure | Up to 375 PSI at 100°F (alloy-dependent; higher ratings available for steel alloys) |
| OEM Part # | Item 100 (Casing / Volute) |
| Our Part # | APP-DM3-G2-100 |
| Max Flow (Group 2) | Up to 1,600 GPM (363 m³/h) |
Cross-Reference & Compatibility
- Fits Pump Series: Flowserve Durco Mark III Group 2 ANSI Pumps
- OEM Part Identification: Casing (Item 100)
- Our Part Number: APP-DM3-G2-100
- Interchangeability: 100% dimensionally interchangeable — bolt pattern, nozzle elevation, and volute centerline match OEM prints exactly
Heavy-Duty Quality Assurance & Wall Thickness
Thicker wall dimensions for maximum corrosion allowance. Unlike standard aftermarket castings that only match the minimum OEM specifications, our Group 2 volute casings are cast with an additional 10–15% wall thickness at all critical wear sections, including the volute cutwater and discharge flange. This heavy-duty design significantly extends service life in abrasive or highly corrosive chemical environments.
Technical Testing & Certification Standards
- Hydrostatic Test Pressure: 100% shell tested at 1.5× maximum allowable working pressure (350–500+ PSI, material-dependent) per HI 14.6 standards.
- Non-Destructive Testing (NDT): 100% visual + dimensional inspection. PMI (Positive Material Identification) and radiography/X-ray testing are available upon request.
- Full Traceability: Every casing is shipped with complete EN 10204 3.1 MTR (Mill Test Reports) and hydrostatic test certificates to ensure compliance for chemical plant installations.
Related Durco Mark III Products
Lead Time & Rush Order Availability
- 📦 Standard Lead Time: 6–10 weeks for exotic alloy castings (CD4MCuN, Hastelloy C-276, Titanium) — manufactured with full EN 10204 3.1 MTR, PMI, and hydrostatic test documentation
- ✅ Stock Availability: Select Group 2 CF8M and CD4MCuN casings may be in stock — contact us for current inventory
- 🔥 Emergency Rush Orders: 3–4 weeks — Request expedited pattern allocation with priority foundry scheduling
Disclaimer: ANSI Pumps Pro is an independent aftermarket manufacturer. Durco and Mark III are registered trademarks of Flowserve Corporation. All OEM part numbers are used for compatibility reference only. We are not affiliated with or endorsed by Flowserve.