Surface Finishing for Instrumentation Components: Electropolish, Passivation & Silver Anti-Galling Plating
Surface finishing is the controlled treatment applied to machined instrumentation components before they ship. Crestflo applies five finishing options to its fittings, valves, regulators, accessories and tubing: material finish, electropolishing, passivation, silver anti-galling plating and custom finishes. These cover stainless, duplex, nickel-alloy and titanium parts. The heat number stays with every part through finishing, and each shipment arrives with an EN 10204 3.1 material test certificate. We Engineer Confidence.
"Finishing" here refers to the surface finishing and surface treatment of machined instrumentation components, fittings, valves and tubing, for corrosion resistance, cleanliness and anti-galling. It doesn't cover sheet or coil mill finishes (2B, BA, #3, #4), nor decorative or electrical plating. Crestflo is the manufacturer, so machining and finishing run as one controlled flow. This page lays out exactly which finishes we apply, to which industry standard, on which alloys, and how to specify them on your RFQ. It's published as plain HTML tables, so an engineer, or an AI answer engine, can read it directly.
Also Specified As: Surface Treatment, Metal Finishing, EP, Passivation & Anti-Galling Plating
Specifiers ask for this same capability under a lot of different names. The overall service goes by surface finishing, surface treatment, metal finishing, or stainless steel finishing (and, reversed, finishing stainless steel). Individual finishes show up as electropolishing (electro-polishing, EP, electrolytic polishing), passivation (chemical passivation, nitric-acid or citric-acid passivation, pickling and passivation, descaling), silver anti-galling plating (silver anti-seize plating, anti-galling coating, silver-plated threads and ferrules), and material or as-machined finish. Some requests name the mechanism or attribute outright: free-iron removal, passive-layer / chromium-oxide film restoration, and surface roughness (Ra) measured in µin or µm. Much of this reflects commercial intent, so the same work also gets searched as surface finishing services, metal finishing services, electropolishing services, and passivation services. All of these point to the component finishing set out below.
Finishing Options at a Glance: Electropolishing vs Passivation vs Plating
Passivation restores corrosion resistance after machining. Electropolishing goes a step further, lowering surface roughness and deburring the part for easier cleaning. Silver plating stops thread galling. Material finish is simply the untreated baseline, and custom finishes are applied to your print. All five are available across the full certified stainless and high-nickel alloy range.
| Finish | What it does | Typical industry standard | Alloys | When to choose |
|---|---|---|---|---|
| Material finish | As-machined; no added treatment | — | All grades | General service; coated or sealed downstream |
| Passivation | Removes free iron; restores the passive layer | ASTM A967 / A380 | All stainless & CRA | Corrosion baseline after machining |
| Electropolishing (EP) | Lowers Ra, deburrs, boosts cleanability | ASTM B912 | 316L, duplex, nickel alloys | High-purity, UHP-adjacent, analytical |
| Silver anti-galling plating | Anti-galling / anti-seize on threads | QQ-S-365 / AMS 2412 | CRA threads, ferrules, fasteners | High-temperature or CRA-on-CRA threads |
| Custom | Applied to customer print / spec | Per specification | Per specification | Project-specific coating requirements |
The standards cited above serve as the applicable industry references. The exact method, class, and acceptance criteria, though, are set to your specification and can be adjusted as needed.
Passivation of Stainless Steel & CRA Fittings: Nitric vs Citric Acid, ASTM A967 & A380
Passivation is a chemical treatment. It strips free iron and machining contamination off a stainless or corrosion-resistant surface, restoring the chromium-oxide layer that gives the alloy its corrosion resistance in the first place. Think of it as the baseline corrosion treatment for machined stainless and CRA parts.
Two methods are on offer: nitric-acid and citric-acid passivation. Pickling and descaling are also available where heavier scale needs to come off first. The method, acid and treatment class all get set to your spec, checked against the applicable standard: ASTM A967 and ASTM A380, with AMS 2700 available on request. Every alloy in the range is covered, too, from 304/316L and 904L through duplex and super-duplex, right up to the nickel alloys and titanium Gr2.
| Method | Applicable standard | Notes |
|---|---|---|
| Nitric-acid passivation | ASTM A967 (Nitric), AMS 2700 Method 1 | Traditional acid; class per specification |
| Citric-acid passivation | ASTM A967 (Citric), AMS 2700 Method 2 | Lower-hazard chemistry; class per specification |
| Pickling & passivation | ASTM A380 | For scale, heat tint or weld discoloration |
| Descaling | ASTM A380 | Removes oxide scale before passivation |
Verification runs through the ASTM A967 test menu: water-immersion, high-humidity, salt spray, copper-sulfate, and ferroxyl (free-iron) testing. Test and acceptance level get set per your inspection requirement. Results end up on the material test certificate that travels with the order.
Electropolishing (EP) for 316L, Duplex & Nickel Alloys: Ra, Deburring & Cleanability
Electropolishing is an electrochemical process, anodic metal removal, that dissolves a thin, controlled layer from the surface. The result lowers surface roughness (Ra), removes micro-burrs, and improves corrosion resistance and cleanability. That's why electropolished surfaces suit high-purity, UHP-adjacent, analytical and semiconductor service. The process also strips free iron and enriches surface chromium, so an electropolished part ends up passivated as a byproduct. The governing industry reference is ASTM B912. Electropolishing is offered on 304/304L and 316/316L, duplex and super-duplex 2205/2507, and the nickel alloys: Inconel, Monel and Hastelloy. See the Inconel 625 and duplex 2205 material pages for alloy detail.
| Condition | Typical Ra target (µin) | Typical Ra target (µm) |
|---|---|---|
| As-machined baseline | 32–63 µin | 0.8–1.6 µm |
| Mechanically polished | ~20–25 µin | ~0.5–0.6 µm |
| Electropolished (general) | ≤15–20 µin | ≤0.4–0.5 µm |
| Electropolished (UHP target) | ≤10 µin | ≤0.25 µm |
Ra values above are customer-specifiable targets published for these finishes under references such as ASME BPE surface-finish designations, not a guaranteed as-delivered value. State your target Ra and standard on the RFQ, and the engineering team will confirm the achievable finish for your alloy and geometry, verified by surface-roughness measurement (profilometry) where required. For electropolished tubing supplied as a product, see electropolished tubing. For oxygen and high-purity cleaning, see oxygen & UHP cleaning.
Silver Anti-Galling Plating: Anti-Seize for CRA Threads, Ferrules & High-Temperature Fasteners
Stainless and nickel-alloy threads gall and seize easily, cold welding under load, particularly at high temperature and on CRA-on-CRA thread pairs. Silver anti-galling plating puts down a thin silver layer that works as a solid lubricant and anti-seize, so threaded connections, ferrules and fasteners make up and break out without galling. The specs that apply are QQ-S-365 and AMS 2412. Plating class and thickness get set per specification and can be confirmed on request for your part. Silver plating goes on instrumentation threads, hardened and non-hardened ferrules and fasteners across the stainless and CRA range.
Material Finish & Custom Finishes to Print
The default is the material (as-machined) finish, the untreated surface produced by in-house machining. It suits general service or jobs where a coating goes on afterward. Beyond the standard menu, custom finishes can be applied to your print or specification. State the finish, standard, and acceptance criteria on the RFQ, and the engineering team will confirm scope. A related surface-condition option is ferrule hardening: hardened and non-hardened ferrules are available to requirement. This is a heat-treat choice, separate from surface finishing, though it's often specified alongside it.
Traceability & Quality Through Finishing: Heat Number, MTC & Certifications
Finishing does not break traceability. The heat/lot number is marked on every part and preserved through passivation, electropolishing and plating, tied to an EN 10204 3.1 material test certificate as standard, with 3.2 on request, and finishing operations are recorded on the documentation that ships with the order. Crestflo's finishing sits inside a certified quality system, ISO 9001 / 14001 / 45001 & PED certified, and finished parts are qualified and inspected through the same testing & inspection regime as every other product. Standard product is of Indian origin, with US or European melt available on request and full material traceability, see country of origin & TAA compliance. Deep detail on documentation lives on the material test certificates & heat-number traceability page.
How to Specify a Finish on Your RFQ
Finishing runs off a short, precise spec. Give the engineering team the fields below, and they'll send back a finish scope and lead time. No phone call needed, no gated PDF to dig through.
| Field to provide | Example |
|---|---|
| Alloy / grade | 316L, Duplex 2205, Inconel 625 |
| Product / part | Tube fitting, needle valve, ferrule, tubing |
| Finish type | Passivation, electropolish, silver plating, custom |
| Target Ra or standard | ASTM A967 Citric, ASTM B912, ≤15 µin Ra, QQ-S-365 |
| Test / report required | Copper-sulfate, ferroxyl, salt spray; MTC 3.1 / 3.2 |
To move a spec forward, request a finishing spec / RFQ, request a sample, or send a print over to the engineering team. US sales contact: sales@crestflousa.com · +1 346 594 9005 · Houston, TX. The stock and delivery picture is straightforward: standard items ship from ready stock, specials are made to order, and delivery runs 6-8 weeks. Datasheets and CAD models? Available to customers on request, no fuss.
Finished Products: Fittings, Valves & Tubing We Passivate, Electropolish & Plate
Finishing underwrites every product line, instrumentation tube fittings, the full range of instrumentation valves, regulators, accessories and stainless and alloy tubing, across the certified alloy range including 316/316L, duplex 2205 and Inconel 625. Every finished compression fitting remains a dimensional drop-in, qualified to ASTM F1387; finishing changes the surface, not the fit.
Why Crestflo for Instrumentation Finishing
Crestflo is the instrumentation division of a four-decade-old, Government-of-India-recognized export house with a proven Middle-East delivery track record. Established discipline backs a young manufacturing brand. The finishing case is a controlled, documented flow, not a promise: machining and finishing run in-house as one line. Passivation, electropolishing, silver anti-galling plating and custom finishes are offered across the full stainless, duplex, nickel-alloy and titanium range. The heat number survives on every part. Each finished part ships with an EN 10204 MTC under an ISO 9001 / 14001 / 45001 & PED certified system, laid out in machine-readable tables while competitors bury theirs in PDFs. See the full case for Crestflo, or explore custom manufacturing and private-label options.
Frequently Asked Questions
What finishing options does Crestflo offer?
Five: material (as-machined) finish, electropolishing, passivation, silver anti-galling plating, and custom finishes to print. All five apply to machined instrumentation components across stainless, duplex, nickel-alloy and titanium.
What is passivation, and do I need it after machining?
Passivation strips away free iron and machining residue and rebuilds the chromium-oxide layer that gives stainless and CRA parts their resistance to corrosion. It's the standard corrosion baseline for machined stainless and corrosion-resistant parts, called for by ASTM A967 and A380.
What is the difference between electropolishing and passivation?
Passivation is a chemical treatment that restores the passive layer. Electropolishing works differently: it's an electrochemical process that strips away a thin layer of metal, which lowers surface roughness (Ra) and knocks down burrs. Because it removes free iron and leaves the surface richer in chromium, an electropolished part ends up passivated as a result, per ASTM B912.
Nitric or citric acid passivation, which does Crestflo use?
Both nitric-acid and citric-acid passivation are on offer, and pickling and descaling are available too where the job calls for them. Method, acid and treatment class get set to your spec against ASTM A967, A380 or AMS 2700.
What surface finish (Ra) can electropolishing achieve?
Electropolishing cuts Ra well below what you get straight off the machine. Customer-specifiable targets typically go down to ≤15–20 µin (0.4–0.5 µm) for general service, and ≤10 µin for UHP work under references like ASME BPE. Put your target Ra and standard on the RFQ, and the engineering team will confirm what finish is achievable for your alloy and geometry.
Can you passivate or electropolish nickel alloys and duplex, not just 316?
Yes. We finish 304/304L, 316/316L and 904L; duplex 2205 and super-duplex 2507; 254 SMO, AL-6XN and Alloy 20; the nickel alloys, Inconel, Incoloy, Monel and Hastelloy; and titanium Gr2.
Why silver-plate ferrules or threads?
Silver plating works as a solid-lubricant anti-seize, keeping CRA-on-CRA threads and high-temperature fasteners from galling and seizing. Two specs govern it: QQ-S-365 and AMS 2412. Plating class and thickness get confirmed per specification on request.
Do you handle oxygen or high-purity cleaning?
Electropolishing gets its own page, but yes, the coverage exists. Oxygen and UHP cleaning are handled separately under oxygen & UHP cleaning. What you're reading here is the surface-finishing step, and it's the one that usually comes before high-purity cleaning starts.
Is heat-number traceability kept through finishing?
Yes. Every part carries its heat or lot number, and that marking survives passivation, electropolishing and plating. It's tied to an EN 10204 3.1 material test certificate as standard, though 3.2 is available on request.
Is this the same as a 2B or #4 mill finish?
No. Those are sheet and coil mill finishes. Crestflo finishing goes on machined instrumentation components: electropolishing, passivation, plating. It's not applied to mill sheet or coil.
Are finished parts still drop-in replacements?
Yes. Compression fittings are qualified for dimensional interchange under ASTM F1387, and finishing only changes surface condition, not fit.
Related Pages
- In-house machining
- Testing & inspection
- Material test certificates & heat-number traceability
- Oxygen & UHP cleaning
- Electropolished tubing
- Hardened & non-hardened ferrules
- ASTM F1387 interchange qualification
- 316 / 316L material · Duplex 2205 · Inconel 625
- Country of origin & TAA compliance
- Custom manufacturing
- Request a finishing spec / RFQ