Pickling, passivation and electropolishing describe different surface-treatment processes. They should not be used as interchangeable finish names on a stainless steel casting order. The correct specification depends on the condition of the surface after casting and machining, the required appearance and the environment in which the component will operate.

A purchase request that says polished and passivated may still leave important questions unanswered. Which surfaces are included? What preparation is required? Is a numerical surface texture specified? How will the final condition be verified? Clarifying these points is more useful than selecting a treatment solely because it sounds like a higher grade of finish.

Start with the surface condition and service

Describe whether the component has heat scale, machining marks, an as-cast texture or contamination from earlier operations. Also identify the intended service, especially where crevices, deposits or difficult cleaning conditions are expected. A surface-treatment decision should support that service rather than conceal a missing material-selection review.

The worldstainless guide to pickling and passivation explains the distinction between cleaning, removing surface scale and supporting the passive surface condition. It provides technical context, not a universal processing recipe for every casting grade.

Use the process name accurately

Pickling is associated with removing oxide scale and affected surface material. Passivation treatments address the surface condition through a different purpose and procedure. Electropolishing removes material electrochemically and can change surface topography. These distinctions matter when the drawing has dimensional or surface requirements.

None of these names alone defines the complete delivery condition. The applicable standard, treatment procedure, prior preparation and verification requirements need to be stated. Processing chemicals and operating conditions should be handled by qualified specialists under an approved procedure, not improvised from an article.

Do not expect passivation to correct geometry

A rough or irregular casting surface does not become dimensionally accurate because it is passivated. If a sealing surface requires machining, specify that operation separately. If an appearance requirement calls for mechanical polishing, identify the relevant surfaces and acceptance criteria.

Likewise, electropolishing should not be treated as a substitute for controlling an oversized edge or an unacceptable casting indication. Where material removal affects a fit, thread or sharp feature, agree the machining allowance and final measurement stage with the supplier.

Include internal surfaces in the review

A treatment that is practical on an open exterior may be difficult to control in a narrow cavity. Access, drainage and rinsing matter. Specify which internal regions require treatment and what evidence is expected, rather than assume that an exterior appearance proves the condition of the whole component.

For an illustrative fluid housing, the visible outside may be cosmetic while the internal passage controls cleanliness. Those objectives can require different checks. The order should distinguish them so that a bright exterior does not become the only basis for acceptance.

Verify the finished condition using the right evidence

Surface texture, cleanliness, chemical-treatment records and corrosion-related tests are different evidence types. Select the required combination through the drawing and applicable standards. A photograph can help document appearance but cannot replace every specified verification. Where a treatment certificate is required, identify the process specification, part or batch reference and required results.

Keep the manufacturing sequence traceable. If further machining or contamination occurs after treatment, the previously recorded surface condition may no longer describe the delivered part. Agree whether treatment is the final operation or whether additional cleaning and verification are needed afterward.

Specify the finish with the casting enquiry

For stainless investment castings, identify the alloy, service environment, treated surfaces and any protected dimensions. Reference the required standard edition and acceptance method. Where the finish is cosmetic, an agreed sample can supplement written criteria.

When you ask Hengke to review a finish, request a route that separates casting cleanup, machining, mechanical finishing and chemical treatment. This makes the proposal easier to compare and helps prevent three different processes from being compressed into an ambiguous line item.