Ductile Iron for Pressure Parts
Who this helps: Design Engineers / Buyers specifying pressure-tight iron castings—pumps, valve bodies, compressors, hydraulic housings—where leakage risk, durability and inspection cost matter.
What you’ll get: a material selection path (gray/grey vs ductile vs ADI), how graphite morphology drives leak paths, DFM rules that prevent porosity/shrinkage at seals, a copy-paste drawing spec, and a right-sized NDT & leak-test plan.
Prepared by YB Metal Solution. Share your drawing via /rfq—YB Metal will return a part-specific material pick, leak-test matrix, and NDT coverage.
Author: YB Metal Solution Engineering Team (hereafter YB Metal)
Table of contents
- Pressure-tight anatomy: where leaks start
- Graphite morphology & leakage risk (gray vs ductile vs ADI)
- Material picks by part family & pressure class
- DFM to stop leak paths: walls, cores, junctions, seals
- NDT & leak-test toolkit: what catches what
- What to put on the drawing (copy–paste)
- Proof it’s tight: pilot plan & evidence pack
- Related internal resources (with slugs)
- What YB Metal delivers
- FAQs
Pressure-tight anatomy: where leaks start
- Sub-surface gas porosity opened by machining on sealing faces/bores.
- Micro/macro-shrinkage at hot spots and T/Y/X junctions behind pressure walls.
- Core print & wash issues (under-baked cores, pooled coating) near fluid passages.
- Thin webs/minimum wall below process capability, especially around threaded ports.
- Surface damage (shot peen embedment, burn-on) compromising coating/impregnation.
Deep-dive on these mechanisms:
Graphite morphology & leakage risk (gray vs ductile vs ADI)
| Material family | Graphite form | Leakage tendency | Where it fits | Notes |
|---|---|---|---|---|
| Gray/grey iron (EN-GJL / ASTM A48) | Flakes → continuous networks | Higher (micro-galvanic & connected flakes may ease leak paths if porosity present) | Low/medium pressure housings, large bases | Great damping & machinability; needs robust porosity/shrink control + coating if outdoors |
| Ductile (SG) iron (EN-GJS / ASTM A536) | Nodules → discontinuous | Lower than gray at equal process control | Preferred for pressure parts (pumps, valves, hydraulic bodies) | Better toughness; supports tight NDT/leak acceptance |
| ADI (ASTM A897 / EN 1564) | Nodular + ausferrite | Similar sealing to ductile | High strength/fatigue parts that also hold pressure | ADI is a strength upgrade, not a sealing upgrade—control porosity/shrinkage like DI |
Background on base grades:
Material picks by part family & pressure class
Pressures shown as bar/psi guides; confirm by code/customer spec.
| Part family | Typical pressure | Common choice | When to upgrade |
|---|---|---|---|
| Pump housings / covers | 6–25 bar (90–360 psi) | EN-GJS-500-7 / 600-3 (A536 80-55-06 / 65-45-12) | Thin walls <6–8 mm (0.24–0.31 in) or high fatigue → ADI 1050-750-07 |
| Valve bodies | 10–40 bar (145–580 psi) | EN-GJS-600-3 / 700-2 | High temp/erosion → DI with alloy (Cu/Ni) + hard seats |
| Compressor covers / manifolds | 8–30 bar (116–435 psi) | EN-GJS-600-3 | Weight/strength push → ADI 1200-850-04 with strict QA |
| Gearbox oil cavities | < 5 bar (≤73 psi) | EN-GJL-250/300 (A48 Cl 35/40) | Shock loads or repeated leaks → move to EN-GJS-500-7 |
Minimum walls & section effects:
- Set realistic walls per grade/process: Wall Thickness Rules
- For DI/ADI, see Minimum Wall for Ductile Iron
DFM to stop leak paths: walls, cores, junctions, seals
Walls & transitions
- Keep uniform walls; avoid abrupt steps near pressure zones.
- Fillets generous: see Fillet & Radius Rules
Cores & prints
- Vent blind cavities; avoid coating pooling; bake to spec.
- Place prints where post-core gas can escape (not into pressure faces).
Hot spots & feeding
- Identify T/Y/X junctions; require directional solidification with risers/chills; validate with cut-ups on pilots.
- Guide: Fix Shrinkage Porosity
Sealing faces & finish
- Machine only what seals; protect as-cast skins elsewhere.
- Surface finish guidance by process: Surface Finish by Process
Tolerances & stock
- Use ISO 8062 CT by size band; don’t starve sealing lands of stock:
- ISO 8062 CT Grades
- Open GD&T Guide
Process choice
- Thin passages → Shell molding improves uniformity/venting:
- Shell Molding for Thin-Wall
- Large/heavy pressure walls → Resin sand for feeding freedom:
- Resin vs Green Sand
- General housings → Green sand often best value:
- Green Sand Casting
NDT & leak-test toolkit: what catches what
| Method | Finds | Good for | Notes |
|---|---|---|---|
| Pressure test (air under water) | Through-leaks (gross to fine) | All pressure parts | Simple & visual; specify pressure/time |
| Dry air decay / differential | Fine leaks quantitatively | Small/medium parts | Repeatable; avoids water contamination |
| Helium mass-spec (sniff/vacuum) | Very fine leaks | Critical valves, thin passages | Highest sensitivity; cost ↑ |
| Dye-penetrant (PT) | Surface-breaking cracks | After machining | Good for seal faces; won’t see subsurface |
| X-ray / CT | Macro-shrinkage, porosity clusters | Hot spots, pilots & root-cause | Plan views & criteria up front |
| UT / MT | Internal flaws / surface cracks | Thick sections / ferritic surfaces | Coverage depends on geometry/finish |
For acceptance, tie test choice to risk class (see drawing text below).
Proof it’s tight: pilot plan & evidence pack
Pilot (3–5 pcs):
- Leak test at operating + safety margin; record pass/fail & rate (cc/min).
- X-ray/CT or cut-ups at predicted hot spots (1–2 pieces).
- Metallography: nodularity %, porosity/shrink class near pressure wall.
- CMM FAI: sealing-face flatness/position; datum stack.
Series control: moisture/LOI windows, core bake logs, pour temp, transfer time (if ADI), riser/chill layouts under doc control.
What YB Metal delivers
YB Metal quotes with a machining plan attached:
- YB Metal Solution quotes with a pressure-part readiness pack:
- Material decision: DI/ADI vs GJL with ASTM⇆EN nearest equivalents, wall & section guidance.
- Leak-test plan: pressure level/time, air vs helium vs water; gage R&R friendly setup.
- NDT map: which zones get X-ray/CT/UT/PT and why.
- Pilot evidence pack: leak logs (bar/psi & cc/min), X-ray/CT images or cut-ups, metallography (nodularity %, porosity class), CMM FAI on sealing stack.
- Need a part-specific plan? Upload your drawing at
/rfq—we’ll return recommendations and a quote.
Upload your drawing via —we’ll return a part-specific plan and quotation.
FAQs
CTA — specify with proof, not guesses
Specify pressure parts with the right graphite morphology, wall rules, and a proof-oriented test plan—before you cut tooling. Upload your drawing to /rfq and YB Metal will return a material + NDT + leak-test package you can run on pilots.