A bulk order of stainless steel filter housings can look fine in the photos and still cause trouble. Common problems include a thread standard that does not match your pipework, a cartridge that will not seat, or an unspecified gasket material. Others are rough internal welds, or a mill certificate that cannot be matched to any part in the carton. Incoming quality control (IQC) is where you catch these problems while the supplier can still replace, rework or credit the goods. This guide gives buyers, quality teams and OEM engineers a practical checklist. It covers what to prepare before the shipment lands, which checks to run on arrival, how to sample a bulk lot, and what to write into the PO so the results hold up in a dispute.
Incoming inspection of filter housings should confirm six things, in this order:
A sampled leak test sits on top of these, with a pressure defined by your approved specification.
The order matters because the checks get slower and more expensive as you go down the list. A wrong label takes seconds to find. A weld defect needs light and a trained eye. A leak test needs equipment and time. Running the cheap checks first lets you reject or quarantine a lot before spending effort on the expensive ones.
Inspectors can only reject what the contract defines as a defect. Four items should exist before the goods arrive.
An approved drawing or specification sheet. It should state the model, material grades for each part, connection type and size, closure type, finish and rated pressure and temperature. Where the supplier publishes ratings, such as the 87 psi (6 bar) and 176°F (80°C) maximum listed on the mobile stainless steel filtration cart page, those figures come with qualifiers. The supplier’s own wording on that page ties them to cartridge, seal and operating conditions. Your acceptance criteria should name the exact conditions you need.
A golden sample or approved first article. Keep one unit, with photos, as the physical reference for finish, weld appearance and fit. “Polished” and “good weld” are subjective until a sample defines them.
A defect classification. Sort defects into three groups:
Each class gets its own rule. A single critical defect can fail a lot, while minor cosmetic marks may be tolerated up to a limit.
A sampling plan. The widely used framework is ISO 2859-1. BSI’s summary of ISO 2859-1:2026 describes AQL-indexed single, double and multiple sampling plans for lot-by-lot inspection. It also covers rules for switching between normal, tightened, reduced and skip-lot inspection. The same summary notes that AQL sampling reduces reliance on costly 100% inspection. The standard supplies the statistical structure. You still decide which characteristics count as critical and which AQL levels fit your risk.
A common assumption is that the safest policy is to inspect every unit for every characteristic. In practice, that usually backfires. Inspectors fatigue, depth of checking drops, and the slow checks (leak tests, material tests) become bottlenecks that get skipped under delivery pressure.
A better rule is to match inspection depth to how costly and how detectable each defect is:
This applies when you have a stable supplier and the housings are not safety-critical. For first orders, new designs, hazardous media or regulated hygienic service, increase sampling and consider third-party witnessing.
A clean pre-shipment inspection report also does not replace incoming inspection. The pre-shipment report describes the lot at the factory. IQC verifies what actually arrived, after transit, against your specific piping and process.
The table below is a working template. Adjust the methods and rejection triggers to your drawing and risk level.
| Stage | What to verify | Typical method | Common rejection triggers |
|---|---|---|---|
| 1. Documents and marking | PO number, model, quantity, batch or serial marks, certificates, traceability | Compare packing list, labels and certificates to the PO | Certificate cannot be tied to the lot; label or model mismatch |
| 2. Material identity | Grade of body, head, basket or mesh, clamps, fasteners | Certificate review, sampled PMI, lab test if disputed | Molybdenum absent in a part specified as 316L; certificate does not match marking |
| 3. Welds and surfaces | Weld continuity, spatter, heat tint, scratches, polish consistency, internal crevices | Visual inspection under good light; borescope or mirror for internals | Cracks, porosity, pits, rough internal welds, rust spots |
| 4. Dimensions and connections | Flange pattern, clamp ferrule size, thread type, port position, element fit | Calipers, thread gauges, fit test with the real element | Thread mismatch, misaligned bolt holes, element does not seat |
| 5. Seals and closures | Gasket or O-ring material, seating, clamp or bolt operation, cover alignment | Visual check, open-and-close test | Wrong elastomer, damaged groove, cover does not seat evenly |
| 6. Pressure and leak | Welds, ports and seals under test | Sampled hydrostatic or other test at the pressure in your approved spec | Any leak, visible deformation |
| 7. Cleanliness and packaging | Internal cleanliness, port protection, carton damage | Visual check, photo record at receiving | Dents, contamination, uncapped ports, moisture staining |
EN 10204 defines standard types of inspection documents for metallic products. Under that catalogue summary, a type 3.1 certificate is issued by the manufacturer and validated by an authorized inspection representative independent of production. A type 3.2 certificate is also signed by the purchaser’s inspector or one designated by official regulation.
If you need a 3.1 or 3.2 certificate, write it into the PO. Then check what it actually covers. A material certificate describes a material heat or lot, not the finished housing. Ask whether the heat number is traceable to the housing body, head and basket. For commodity housings, lot-level traceability is often what you will realistically get. For critical service, require part-level marking.
Specifying 304 or 316L is easy. Proving it on a delivered unit takes more care.
Inspect welds on both outside and inside surfaces. Look for incomplete fusion, cracks, porosity, undercut, spatter and heat tint. Heat tint is the straw-to-blue discoloration near welds, and it signals a surface that may need cleaning before it resists corrosion as expected. Rust spots on new stainless often point to iron contamination from tools or handling, not to a wrong grade. In either case, ask the supplier about its descaling and passivation practice.
ASTM A967 covers several chemical passivation treatments for stainless steel parts and includes recommendations and precautions for descaling, cleaning and passivation. If you need passivation, state the standard and method in the PO, along with any test or documentation you require.
For hygienic housings, finish is the second trap after material. “Polished” is not a specification. State a roughness limit (Ra), where it is measured (inside wetted surfaces versus outside), and how it is verified. Alfa Laval explains that Ra is an average of surface peaks and valleys. It also cautions against treating Ra as a complete indicator of hygienic quality, so pair the number with visual and cleanability criteria. Many food and process-water applications do not require bioprocessing-grade finishes, so specify what your process needs rather than the strictest grade on the market.
Fit errors are among the most frequent and most avoidable IQC failures, because they come from small spec differences rather than poor workmanship. Check:
The last item is the one most often skipped. Fit-test the real consumable, not a drawing dimension. A housing that is dimensionally “in tolerance” can still fail to seal a bag or cartridge that has its own tolerance stack.
Illustrative example (hypothetical, not a customer case): a distributor receives 300 housings with female threaded ports. Sample checks pass visual and weld criteria, but a thread-gauge check shows the ports are a different standard from the buyer’s pipework. A 100% check of port type, which takes seconds per unit, would have caught this at the dock.
Verify the gasket or O-ring material against the process fluid and temperature, and confirm it is seated correctly in a clean groove. Open and close every sampled closure. Clamp-band closures, swing eye bolts and bolted covers should engage without galling, and the cover should seat evenly.
If a leak test is part of your acceptance plan, three rules apply:
The generic checklist above is the base. Each housing design adds its own failure points.
Housings and strainers that look similar in a catalogue fail in different ways. A sintered element behaves differently from a perforated basket, and a clamp closure differs from a bolted flange cover.
| Housing type | Highest-risk checks | Fit verification |
|---|---|---|
| Sanitary cartridge housing | Weld and finish on wetted surfaces, clamp gasket seating, vent and gauge ports | Clamp ferrule size, cartridge seating |
| Single cartridge housing (threaded) | Thread standard, closure sealing, head casting surface, gasket material | Mesh or cartridge element fit |
| Flanged sintered housing | Flange facing and bolt pattern, bolted cover alignment, element seating | Flange standard against your piping |
| Basket strainer | Basket condition, perforation or mesh specification, cover and bolts, drain | Basket seats fully in body, cover closes |
| Side-entry bag housing | Seal surface where the bag ring sits, cover bolts, inlet and outlet position | Correct bag size (#1 or #2) and bag-ring fit |
| Mobile filtration cart | Pump and piping welds, valve and gauge function, frame and wheels | Connection sizes, electrical and pump compatibility |
For sanitary service, the stainless steel sanitary cartridge filter housing page describes a polished vessel with clamp connections, a pressure gauge, a vent connection and a clamp-band closure. For this style, prioritize finish, clamp-gasket seating and vent and gauge ports. For threaded designs such as the stainless steel single cartridge filter housing, which lists threaded ports, a quick-release clamp and a removable mesh element, thread standard and closure sealing move to the top of the list.
Where the pipeline is flanged, as with the flanged stainless steel sintered cartridge filter housing, compare the flange standard, bolt circle and facing against your piping before anything else. Confirm the sintered element seats correctly, and check the cover alignment. Sintered elements also bring a media-specific question: whether the delivered element’s rating and material match the specification.
Basket strainers deserve their own look because their “filter” is a perforated or mesh-lined basket. The stainless steel basket strainer page lists a lift-out perforated basket, optional wire-mesh lining and swing-eye-bolt cover, with filtration ratings set by perforation and mesh selection. Measure and record the perforation or mesh specification, confirm the basket seats fully, and check that the bolts and cover close evenly. The industrial basket strainer with a quick-access cover is described with a bottom drain, pressure gauge and vent arrangement. When that is your configuration, test the drain and gauge ports as part of the functional check, not as afterthoughts.
For bag-style units, bag size is the compatibility check that gets missed. The side-entry stainless steel bag filter housing page states that #1 and #2 are the standard bag sizes for that configuration. Confirm the delivered housing matches the bag size you stock, and fit a real bag to check the seal at the bag ring. Integrated skids need their own plan. If you buy complete assemblies, treat the pump, valves, instruments and piping as separate inspection items alongside the housings.
Decide in advance what happens when a lot fails.
Incoming inspection works only if the order documents give you something to inspect against. Before you send an RFQ for a bulk order, prepare the following:
If you are sourcing from a manufacturer for the first time, ask for a sample unit and the inspection records that will accompany the lot before you place the full order. Send these requirements with your quote request so the supplier can price and plan inspection into production.
It is a structured list of checks a buyer runs on receiving filter housings. It covers documents, material identity, welds and finish, dimensions and connections, seals and closures, leak testing and packaging damage. Each check has a method and a defined accept or reject criterion.
Use a sampling plan such as ISO 2859-1 rather than a fixed percentage. Check fast, critical features like connection type on every unit, and sample slower checks like PMI and pressure tests. Tighten sampling for first orders, new suppliers or after a failure.
It can confirm molybdenum, which separates 316-type from 304-type steel, but handheld XRF generally cannot measure carbon. Confirming the low-carbon “L” grade relies on the mill certificate or laboratory analysis. Test each specified component separately, because the body and fittings may differ.
Not always. It is worth requiring when material traceability matters, such as hygienic, chemical or regulated service. A 3.1 certificate is manufacturer-issued and validated by an independent authorized representative. Confirm what lot or heat it covers and whether it links to marked parts.
Specify a roughness limit (Ra), the surface it applies to and the verification method in the PO. Then measure sampled units with a surface-roughness tester and inspect welds and wetted surfaces visually. Ra alone does not describe cleanability, so also compare against the golden sample.
Usually not. Sample-based testing is common, with 100% testing reserved for critical or hazardous service. Use the test pressure from your approved specification and the applicable code, and never exceed the rating of gauges, gaskets or fittings in the test setup.
Quarantine the lot, document defects with photos and measurements, and notify the supplier within the claim period in your PO. Request replacement, rework or credit as agreed, require corrective action for repeat defects, and re-inspect the corrected lot under tightened sampling.
