The pump sends water through the test connection, closures contain it inside the compressor casing, and the gauge and overpressure protection monitor the resulting pressure boundary. Follow that path before assigning a directive: identify every pressure-retaining component, its function, and whether pressure drives its design.
What path carries the test pressure?
Layer one first. The proposed installation fills a gas-turbine compressor casing with water, raises it to 13.95 bar, and holds it for approximately one hour. The casing passes when it remains at pressure. The installation will perform four tests and then be discarded.
| Path element | Function during the test | Classification question |
|---|---|---|
| Pump | Creates flow and raises pressure | Is its pressure-bearing housing excluded because pressure is secondary to the machine function? |
| Direct connector or hose | Carries pressurized water to the casing | Is it separate pressure equipment, part of an assembly, or integral to the pump arrangement? |
| Seals and closures | Close the casing openings | Are these test tools whose primary function is pressure retention? |
| Compressor casing | Contains the test water temporarily | Does the machinery exclusion still govern when the casing is used as a hydrostatic test boundary? |
| Manometer | Indicates test pressure | What range, accuracy, and protection are required by the test specification? |
| Overpressure protection | Limits unintended pressure rise | Which component protects the weakest pressure-retaining part? |
The hydraulic boundary does not end where the normal compressor boundary ends. During testing it includes every wetted component between the pump outlet and each closure. A direct-mounted pump shortens that path; a remote pump adds a hose or tube. Neither arrangement removes the pressure-retaining function of the intervening hardware.
What exactly needs to be classified?
Separate the production component from the temporary test installation. The compressor casing is designed for a gas-turbine engine whose assembled purpose is power generation. The seals, connections, gauge, protective device, and test controls are designed specifically to create and control a temporary hydrostatic boundary.
The cited PED exclusion concerns casings or machinery whose dimensions, materials, and manufacturing rules are based primarily on strength, rigidity, stability, dynamic effects, or other operational characteristics, and for which pressure is not a significant design factor. Its examples include engines, turbines, turbo-generators, compressors, pumps, and actuating devices. That functional test may support exclusion of a compressor or pump in its intended service; it does not automatically classify every accessory connected during a pressure test.
| Item | Normal or test purpose | Design factor to document |
|---|---|---|
| Compressor casing | Engine component being tested | Whether operating loads rather than contained pressure primarily determine its design |
| Temporary closure | Retains test water | Pressure load, attachment load, sealing force, and credible release mode |
| Hose or tubing | Transfers test pressure | Pressure rating, end connections, restraint, and compatibility with water |
| Gauge and protective device | Measures and limits pressure | Relationship between indicated pressure, trip or relief setting, and the weakest component |
Temporary use does not change the load path. Four planned tests reduce exposure time but do not reduce the force acting on a closure at 13.95 bar. Record the intended number of cycles as a design input rather than treating disposal as a scope exemption.
Which PED and machinery interpretations are available?
| Approach | Reasoning | Practical consequence | Weak point |
|---|---|---|---|
| Exclude the complete arrangement as compressor machinery | The casing and pump belong to machinery for which pressure is not the primary design factor | Address the installation under machinery requirements | It can conceal the pressure-retaining purpose of the temporary closures, hose, and protective components |
| Treat a remote-pump arrangement as pressure equipment | A hose-fed casing resembles an externally pressurized vessel and adds a distinct pressure line | Classify the vessel boundary and hose under PED; the reported outcome was Category I, Module A
|
Using physical mounting as the deciding test does not explain why identical pressure hazards change when the hose becomes shorter |
| Classify each functional boundary, then assess the assembly | The compressor casing, pump, closures, connecting line, gauge, and protection can have different primary functions | Apply the machinery exclusion only to items that satisfy its functional test and assess the remaining pressure boundary separately | Requires a written boundary drawing and a component-by-component scope decision |
The evidence also contains two different references for the same PED exclusion: paragraph 3.10 in one copy and exception 3.6 in Article 1 in another description. Resolve that numbering discrepancy against the exact directive edition and language used for the conformity file. Do not transfer a paragraph number from one consolidated or translated copy into another without checking its text.
A separate interpretation states that pressure equipment incorporated into machinery is excluded only up to Category I, while categories II, III, and IV remain within PED scope. It also points to the machinery directive rule that hazards covered more specifically by another Community directive are handled by that directive. Verify both propositions against the applicable directive text before using them in the declaration or technical file.
Why is pump mounting an unreliable deciding criterion?
Mounting changes the physical configuration, but the decisive engineering questions remain function and boundary. If the pump is bolted directly to a closure, the closure still resists pressure and transfers separating force into its fasteners or restraint. If the pump stands beside the casing, the hose becomes another pressure-retaining component, but the casing and seals see substantially the same test pressure.
| Observation | Possible cause | Decision check |
|---|---|---|
| Direct connection is described as a compressor assembly | The pump and casing are being treated as one machine | Identify whether each temporary closure was designed primarily for pressure retention |
| Adding a hose changes the proposed directive | The hose makes the external pressure boundary visually obvious | Draw the boundary for both arrangements and compare functions, not distance |
| The casing is called an external pressure vessel during testing | Its temporary test function is being substituted for its intended operating function | Record separately the casing's intended service and the test fixture's intended service |
| The complete system is called machinery | Machine identity is being extended to all accessories | List which pressure hazards are specifically covered elsewhere and which remain machinery hazards |
Connection method can still affect the result when it changes what is supplied as a unit, who places that unit into service, or which components form the declared assembly. Those commercial and conformity boundaries must appear on the drawing; physical proximity alone is not a technical classification rule.
Which approach should govern this project?
Use component-by-component classification followed by an assembly assessment. It handles both supported interpretations without making pump location the sole test. Begin with the compressor casing's intended function, apply the cited machinery exclusion test to the casing and pump individually, and then examine the temporary equipment whose primary task is retaining, measuring, conveying, or limiting pressure.
Treat the reported Category I, Module A result as a classification input that requires confirmation, not as a property created by direct or remote mounting. Recalculate the category from the actual boundary data required by the applicable PED classification tables. Obtain the casing volume and applicable fluid classification from the manufacturer, because pressure alone does not reproduce that categorization.
The machinery assessment and PED assessment are not necessarily all-or-nothing alternatives. A machine can contain components or hazards addressed by another directive. The technical file should state which directive governs each hazard and why, preventing both duplicate treatment and an unassigned pressure hazard.
How should the scope decision be documented?
- Draw the complete wetted path from the pump outlet through the connector or hose, casing, closures, gauge branch, and overpressure device.
- Mark the maximum intended test pressure as 13.95 bar and record the approximately one-hour hold period. Identify whether the pump remains connected and capable of adding pressure during the hold.
- List every pressure-retaining item and its weakest allowable pressure. Read ratings from the component marking, certificate, drawing, or datasheet rather than inferring them from pump capability.
- State the intended function of each item. Distinguish normal compressor operation from temporary hydrostatic testing.
- Apply the wording of the cited machinery exclusion to the casing and pump: document which loads primarily determine dimensions, material selection, and manufacturing rules, and whether pressure is a significant design factor.
- Assess the closures, hose or tubing, manifold, gauge connection, and protective device separately. Their test function may differ from that of the compressor casing.
- Verify the correct numbering and wording of the PED exclusion and the interaction with
2006/42/ECin the editions used for the project. - Confirm the reported
Category I, Module Aclassification using the final pressure boundary, volume, fluid information, and supply configuration. - Send one consolidated question set to the manufacturer: pump arrangement, connection drawing, casing volume, test acceptance criterion, allowable casing pressure, permitted closure loads, required gauge characteristics, protective-device requirements, and responsibility for the assembled test installation.
- Record the final scope determination and its rationale in the design report before releasing closure calculations or procurement specifications.
How is the completed installation verified?
Verification must follow the same boundary used for classification. Check component identities and ratings against the drawing, confirm that the pressure-limiting device protects the lowest-rated part, and confirm that the gauge can resolve the test and protective settings required by the approved procedure.
Remove trapped air as the approved filling procedure requires. Water is far less compressible than gas; an air pocket increases stored energy and makes a closure failure more violent. Restrain hoses and removable closures against the actual separating-force path, and keep personnel outside the potential release trajectory during pressurization.
A one-hour pressure indication is not, by itself, a complete leak decision. Isolate or define pump operation during the hold, record starting and ending pressure, observe visible leakage, and account for temperature-related pressure movement under the approved acceptance criteria. The final test record must identify the casing, fixture configuration, calibrated instrument used, achieved pressure, hold duration, observations, and acceptance decision.
FAQ
What happens if the pump is mounted directly on the seal?
The pressure path becomes shorter, but the seal and closure still retain 13.95 bar. Classify their function and the supplied assembly boundary; do not use direct mounting alone as the PED exclusion test.
What happens if the pump connects through a hose?
The hose and its end connections join the wetted pressure boundary and need documented ratings and restraint. The added hose does not, by itself, decide whether the compressor casing is excluded.
What happens if the test rig is used only four times?
The planned four tests are design-cycle and exposure inputs, not a reduction in the pressure force. Document them, but classify and protect every pressure-retaining component for the intended 13.95 bar test.
What happens if the casing qualifies for the machinery exclusion?
Assess the temporary closures, hose or tubing, gauge branch, and overpressure protection separately. Their primary purpose may be pressure retention or pressure control even when the compressor casing is excluded.
How do I verify the final PED classification?
Confirm the applicable directive wording, pressure boundary, casing volume, fluid information, component functions, and supply configuration, then repeat the category assessment. Complete the final verification by matching every installed component and protective setting to the approved boundary drawing and recorded scope decision.