01 / Capability is not service pressure
StelTank has in-house hydrostatic test capability for the tank body up to 0.8 MPa, subject to the customer drawing and an agreed test procedure. That statement describes the upper boundary of an available factory operation. It is not a universal working pressure, a design recommendation, a rating for every tank, or evidence that an unspecified tank is suitable for a particular chemical service.
Three numbers that appear near one another in a project file can answer three different questions. The customer's working pressure describes an operating condition. The customer's design pressure belongs to the design basis used with the selected geometry, material, load cases and governing requirements. The hydrostatic test pressure is a temporary verification value established by the applicable design authority and project procedure. Substituting one for another breaks the chain between service duty, design and verification.
A manufacturing quotation should therefore begin with a sentence, not a number: what does the proposed test have to demonstrate, and under which approved requirement? The answer might concern the tank body, a defined welded boundary, an assembled interface set, or another explicitly identified scope. StelTank can review whether that requested operation is practical within its manufacturing setup, but it does not reverse-engineer the customer's process design from the proposed test value.
The same distinction applies after a successful test. A completed hydrostatic check supports only the acceptance statement written into its procedure. It does not establish chemical compatibility, fatigue life, vacuum resistance, thermal performance, seismic adequacy, nozzle-load capacity, transport suitability or long-term corrosion allowance unless those matters were separately designed and verified by the responsible party. A test report should never be used to imply conclusions that the test was not configured to address.
02 / Keep the design basis with the customer
The customer owns the process design, operating conditions, stored medium, required capacity, overall geometry, design pressure, governing requirements and external interfaces. Those inputs define what the equipment must do. They also identify conditions that a manufacturing team cannot infer from a shell drawing alone: filling and emptying cases, liquid density, temperature range, vacuum or venting conditions, external loads, cleaning chemistry, connected piping reactions and site-specific constraints.
StelTank's role starts from that approved definition. The manufacturing review asks whether the geometry can be formed and joined, whether seams and nozzles are accessible, how the tank can be supported during fabrication and testing, which temporary fittings are needed, how the complete assembly is staged, and what inspection evidence can be produced. A DFM comment can request clarification or propose a buildable alternative. It does not transfer ownership of the service basis to the fabricator.
This division of responsibility should be visible in the purchase package. The drawing or referenced specification should state the required test value and its derivation authority, rather than asking the shop to select a value from its equipment limit. It should also state whether the test is required before or after installation of specified nozzles, closures, frames, valves or other agreed components. If a design revision changes the boundary or a connected item, the procedure must be reviewed again instead of being carried forward by file name alone.
Requirements above the approved in-house capability need a separate drawing, procedure and applicable-authorization review before quotation. The correct outcome may be a revised manufacturing sequence, an explicitly qualified external route, a different test stage or a decision that the proposed work is outside scope. None of those possibilities should be represented as an internal capability until the actual project route and responsibility split have been confirmed.
03 / Define the exact test boundary
"Test the tank" is not a complete boundary definition. The procedure needs a marked drawing or equivalent schedule showing every included shell course, head, cone, transition, nozzle neck, flange, manway, permanent closure and temporary closure. It should identify which valves or instruments are installed, removed, isolated or replaced by blanks, and which connections are used for filling, venting, draining and measurement.
Boundary geometry is not an administrative detail. Al-Gahtani and co-authors used finite-element models to compare a proposed local hydrostatic test around cylindrical nozzle-to-vessel junctions with a full test. Their results showed that the selected cap size changed the stress field and that some apparently convenient local boundaries did not reproduce the full-test condition [1]. That paper addresses a specific family of cylindrical geometries; it does not provide a universal local-test rule for chemical tanks. Its useful lesson here is narrower: changing the tested volume or closure geometry can change what the test represents.
The boundary drawing should also distinguish permanent product parts from temporary test hardware. Temporary heads, blinds, gaskets, hoses, manifolds, supports and adapters need their own identification and control. Their presence in a test photograph does not make them part of the delivered configuration. Conversely, a delivered interface that was excluded from the test needs an explicit note so the record cannot be read later as evidence for an untested joint.
Define the test state as carefully as the physical perimeter. State the drawing revision, manufacturing stage, heat-treatment or surface-treatment state if relevant, installed support condition, orientation, and whether the frame or skid participates. If the tank will be tested in an orientation different from service or transport, the customer must confirm that the temporary loading case is acceptable under the governing design basis.
04 / Plan fill, vent, support and safety
A hydrostatic test is a controlled manufacturing operation, not simply a gauge connected to a filled shell. The procedure should identify the test liquid, its cleanliness or compatibility constraints, the fill point, all high-point vents, the drain route, exclusion controls, communication method and the people authorized to start, pause and release the operation. These details are project-specific; this article is a handoff guide, not a substitute test instruction.
The liquid mass belongs in the temporary load review. Simpson's peer-reviewed comparison of hydrostatic and pneumatic pipeline testing emphasizes that test-fluid selection has to consider the risk of the entire operation, including the mass of liquid on supports and the energy associated with the pressurized fluid [2]. The paper concerns pipelines rather than fabricated tanks, so it cannot select a medium or support arrangement for a StelTank project. It does support asking who has checked the complete temporary setup instead of treating water as consequence-free.
Venting is another boundary question. The agreed fill sequence should provide a way to displace air from the specified high points and should state how operators confirm the required condition before pressure is increased. Because trapped gas changes the energy profile of the test system, the accepted procedure must address it within the project risk assessment [2]. StelTank should not invent a venting rule when the geometry or customer's governing requirement is unknown.
Supports must be reviewed in the actual test orientation. Permanent legs or a frame may be part of the accepted condition, or temporary saddles and restraints may be needed for manufacturing access. The drawing package should show where load can be introduced without damaging finished surfaces or obstructing inspection. Any temporary restraint that affects deformation or access should appear on the test sketch and be removed only through a controlled release step.
Preparation also includes cleanliness, visible access and leakage management. Welds and interfaces that must be observed cannot be hidden by packing, insulation, uncontrolled coating, standing water or temporary equipment. The customer should define any required water quality, post-test draining, drying, preservation and disposal constraints for the actual medium and material system. StelTank reviews how those requirements fit the manufacturing route; it does not select process-cleanliness criteria on the customer's behalf.
05 / Agree the procedure and acceptance
The test procedure should be approved before the operation begins. At minimum, it needs the governing drawing and revision, responsible parties, exact boundary, liquid, test orientation, fill and vent sequence, pressure stages, stabilization or hold requirements, inspection points, permitted adjustments, stop conditions, depressurization, drain and restoration steps. The responsible design authority supplies or approves the values and acceptance rules; StelTank checks whether the sequence can be executed safely and repeatably in the agreed manufacturing scope.
Pressure instrumentation needs more than a readable display. Record the instrument identity, usable range, calibration status, connection location and the source of the acceptance reading. If multiple indicators are required, the procedure should state which one governs and how disagreement is handled. ISO 10012 specifies requirements for measurement processes and measuring equipment when that standard is contractually invoked [3]. Referencing it here does not assert that it governs every project or that StelTank holds a particular certification.
If the customer requires results from a laboratory operating to ISO/IEC 17025, the required activity and current scope must be confirmed with the selected laboratory; the standard addresses competence, impartiality and consistent operation of testing and calibration laboratories [4]. A calibration sticker, a laboratory name or a general accreditation statement is not enough to prove that a particular requested service falls within scope. The purchase requirement should say what evidence must accompany the instrument or result.
Acceptance language should separate observation from disposition. "No visible leakage at the identified pressure during the stated inspection period" is a different record from "accepted for service." The first can be an observed test result under a defined procedure. The second depends on the customer's design basis, governing requirements and approval authority. The test sheet should name the person or organization authorized to make the final disposition.
Do not improvise a response to a leak, unstable reading, unexpected deformation, damaged temporary fitting or interrupted test. The procedure should define stop, depressurization, investigation, repair approval, repeat-test and record-retention routes before production pressure creates a schedule conflict. A repeat test needs a new traceable entry; overwriting the first result erases information needed to understand the final condition.
| Control point | Customer or design authority confirms | StelTank manufacturing review | Record retained |
|---|---|---|---|
| Service basis | Operating cases, medium, design pressure and governing requirements | Questions affecting fabrication and temporary test setup | Approved input revision |
| Test definition | Required pressure, duration, acceptance and disposition authority | Practical sequence, access and equipment range | Approved procedure |
| Boundary | Included product interfaces and permitted exclusions | Blinds, fill, vent, drain, supports and temporary hardware | Marked boundary drawing |
| Measurement | Required accuracy, traceability and reporting basis | Instrument location, identification and readable range | Instrument and calibration references |
| Release | Who accepts, rejects or approves further action | Drain, dry, restore, protect and hand off | Signed result and disposition |
06 / Build an auditable test record
A useful record allows a later reviewer to reconstruct what was tested without relying on memory. Identify the customer project, part or assembly, drawing revision, serial or batch identity if assigned, date, location, procedure revision, boundary, test orientation, liquid, instruments, operators, witnesses and approvers. Attach the marked boundary and any approved deviation rather than expecting a generic certificate title to carry that information.
Record the required stages and actual observations in the format agreed before the test. Photographs can help show setup and visible condition, but they do not replace instrument data, identities or signatures. Any image must be tied to the same product and revision, and sensitive drawing content should be controlled under the project's confidentiality route. The representative images on this page are illustrative and are not test evidence for a customer tank.
Nonconformities and interruptions belong in the same traceability chain. State what occurred, when the system was depressurized, what investigation or repair was authorized, which revision governed the action, and whether a complete repeat was required. The final report should make the sequence visible instead of presenting only the last successful observation.
Closeout matters because water remaining after a test may conflict with the customer's delivery or process requirements. The customer should specify draining, drying, cleanliness, preservation and protection expectations. StelTank can plan access and manufacturing steps around those instructions. It cannot infer a chemically acceptable residual condition without the customer's medium and service knowledge.
Before filling, hold a documented readiness review against the actual tank and current procedure. Confirm product identity and revision, installed and excluded interfaces, closure identification, support condition, vent and drain access, instrument identity, calibration evidence, inspection visibility, communication roles and the approved stop route. Record unresolved items and close them through the named authority instead of treating the checklist as permission to improvise. The completed readiness record does not replace the test procedure; it shows that the procedure, hardware and product state were reconciled at the point of execution.
07 / Send a complete test inquiry
For a feasibility review, send the latest controlled drawing, the customer-owned service basis, the requested test procedure or governing reference, and a clear interface list. Mark the test boundary and delivery condition. Identify whether the requirement applies to the tank body alone or to an agreed assembly stage, and distinguish permanent product items from temporary test hardware.
Also state the evidence expected at handoff: marked drawing, instrument list, calibration references, pressure and time record, inspection observations, photographs, witness signatures, deviation log or another contractually defined package. If an independent witness or laboratory is required, identify the requested scope before quotation. An NDA can be agreed before detailed drawings are exchanged.
The manufacturing response should then list assumptions, exclusions and open decisions. A credible answer may confirm that the proposed operation fits the available setup, request a geometry or access change, recommend a different manufacturing stage, or flag the requirement for separate authorization review. It should never turn the facility limit into a product rating or treat an unapproved procedure as settled.
- Latest drawing and model revision, with the controlling document identified.
- Customer-defined medium, operating conditions, capacity, geometry, design pressure, governing requirements and interfaces.
- Required hydrostatic test value and the authority or specification from which it comes.
- Marked test boundary, exclusions, temporary closures, orientation, supports, fill, vent and drain points.
- Acceptance, witness, measurement, record, drying, preservation and release requirements.
- Named owners for clarification, procedure approval, nonconformity disposition and final acceptance.
References
The journal papers below support only the bounded technical statements cited in the text. They do not define the design or test pressure for a customer tank. The official standards are normative only when the applicable contract, customer requirement or approved procedure invokes them in the relevant scope and edition.
- H. Al-Gahtani, A. Khathlan, M. Sunar and M. Naffa'a, "Local Hydrostatic Pressure Test for Cylindrical Vessels," Journal of Pressure Vessel Technology, 139(1), published online 2016. https://doi.org/10.1115/1.4033533
- D. A. Simpson, "Comparative Risks of Hydrostatic and Pneumatic Pipeline Testing," Journal of Pressure Vessel Technology, 142(5), 2020. https://doi.org/10.1115/1.4046981
- ISO 10012:2003, Measurement management systems — Requirements for measurement processes and measuring equipment. Official ISO record
- ISO/IEC 17025:2017, General requirements for the competence of testing and calibration laboratories. Official ISO record