SAFETY VALVE ENGINEERING
Sizing starts with the relieving case—not the existing valve size.
HHSV converts a defined relieving load and service condition into a calculated discharge area, selectable valve configuration and reviewable technical quotation using the project-specified API 520 or ISO 4126 route.
ENGINEERING OUTPUT
Calculated. Selected. Documented.
01
Relieving case
Client or process engineer defines the credible scenario and required load.
02
Sizing basis
Fluid properties, pressures, temperature and backpressure are verified.
03
Valve selection
Required area is matched to a suitable product, orifice and configuration.
04
Technical quote
Calculation, datasheet, drawing, compliance status and scope are submitted.
REQUIRED INPUTS
Six data groups establish the minimum sizing basis.
Incomplete data can be marked unknown, but no final valve size should be inferred from a nameplate, line size or set pressure alone.
01
Medium and phase
Fluid name, composition and whether the relieving condition is gas, vapor, steam, liquid or two-phase.
02
Required capacity
Mass or volumetric relieving rate, unit, basis conditions and the governing relief scenario.
03
Pressure data
Operating pressure, MAWP when applicable, set pressure, allowable overpressure and relieving pressure.
04
Temperature
Operating and relieving temperature, including any low-temperature or high-temperature design condition.
05
Backpressure
Superimposed and built-up backpressure, whether constant or variable, and the outlet-system basis.
06
Connection and scope
Inlet/outlet size, rating, facing, material, standard, certification, quantity and inspection requirements.
SIZING DATA TABLE
What to provide and why it changes the result.
Units, pressure reference and basis conditions must be stated; avoid unlabeled spreadsheet values.
FIELD
MINIMUM INPUT
USE IN REVIEW
Relieving load
Value + unit + calculation owner
Sets the required capacity; not derived from valve size
Fluid / phase
Composition and state at relief
Selects the applicable sizing method and fluid properties
Operating pressure
Normal and maximum expected
Checks margin below set pressure and operating stability
Set / relieving pressure
Gauge basis and allowable overpressure
Establishes the pressure used in the capacity calculation
Relieving temperature
Temperature at the valve inlet
Affects properties, materials and correction factors
Backpressure
Superimposed + built-up; constant or variable
Influences configuration and correction method
Connections / code
Size, class, facing and project standard
Controls physical selection and approval scope
Required documents
Calculation, drawing, certificates, ITP/MDR
Defines the technical quotation and delivery boundary
ENGINEERING WORKFLOW
Six steps from relief case to technical quotation.
Desktop uses a native six-column grid. Tablet changes to three columns and mobile to one without changing the sequence.
01
Define case
Confirm the credible relief scenario and required relieving load
02
Verify fluid
Establish phase, composition and properties at relieving conditions
03
Set pressures
Confirm set pressure, overpressure and total backpressure basis
04
Calculate area
Apply the project-specified API 520 or ISO 4126 method
05
Select valve
Choose an orifice, model, material and backpressure configuration
06
Submit quote
Issue calculation, datasheet, drawing, deviations and delivery scope
CALCULATION ROUTE
Use the project standard as the calculation basis—not as interchangeable wording.
HHSV confirms the standard, edition, scope and any owner-specific rules during technical review.
SIZING AND SELECTION
API 520 route
Used when the project specification requires API sizing and selection. The calculation basis, fluid case, coefficients, backpressure treatment and selected valve data are stated in the submittal.
API 520 is not a generic certification statement; the supplied product’s actual certification and nameplate scope are checked separately.
SAFETY DEVICES
ISO 4126 route
Used when ISO 4126 is the specified design and calculation framework. The relevant part, fluid case and product configuration are confirmed before final selection.
A valve designed or calculated to an ISO method is not automatically certified for every ISO 4126 product category or application.
SELECTION REVIEW
The calculated area is only one selection input.
ENGINEERING CHECKS
Before the model and orifice are fixed.
The selected certified orifice or effective discharge area must meet or exceed the calculated requirement, but configuration and operating behavior still require engineering review.
- Gas, vapor, steam, liquid or two-phase condition
- Compressibility, viscosity and other applicable fluid corrections
- Constant or variable superimposed backpressure
- Built-up backpressure and outlet-line assumptions
- Operating margin below set pressure and risk of simmer or chatter
- Material, temperature, corrosion and certification constraints
TECHNICAL QUOTATION
A review package, not a price-only response.
The exact document set depends on enquiry maturity and customer requirements.
01
Sizing basis
Service data, relief case, assumptions, units and applicable calculation route
02
Calculation sheet
Required discharge area, selected orifice and relevant correction basis
03
Valve datasheet
Model, configuration, size, rating, materials, set pressure and temperature
04
GA drawing
Dimensions, connections, weights and installation interfaces where available
05
Compliance package
Certificate matrix, designed/tested/certified status and deviations
06
Commercial boundary
Price, Incoterm, inspection, documents, delivery schedule and exclusions
START WITH AVAILABLE DATA
An RFQ, datasheet or nameplate photo is enough to begin clarification.
STOP AND CLARIFY
Do not finalize the selection when the relief basis is uncertain.
- Required relieving rate is missing or has no calculation owner
- Pressure values mix gauge and absolute references
- Fluid phase or composition at relief is uncertain
- Backpressure is unknown, variable or based on an unreviewed outlet line
- Two-phase flow is possible but no approved method is specified
- Certification requested does not match the selected model or nameplate scope