HTO conventional safety relief valve and HTB balanced-bellows safety relief valve

Set Pressure and Protected Equipment

Establish the required set pressure using the applicable design basis and the allowable pressure limits of the protected equipment.

• Protected vessel, pipeline or process equipment
• Design pressure and applicable pressure limits
• Required set pressure and pressure units
• Applicable code, project specification and governing requirements

Required Capacity and Overpressure Scenario

Valve sizing must be based on the governing relief case rather than normal operating conditions alone.

• Credible cause of overpressure
• Required relieving rate or engineering sizing calculation
• Fluid composition and relevant physical properties
• Relieving pressure and temperature

Backpressure Evaluation

Establish the pressure conditions at the valve outlet before deciding whether a conventional or balanced-bellows arrangement is suitable.

• Superimposed backpressure at the discharge connection
• Built-up backpressure during relief
• Discharge header pressure variation
• Outlet piping and discharge-system configuration

Process Compatibility

Materials and internal configuration must be compatible with the process medium and the specified operating and relieving conditions.

• Fluid phase and corrosive or erosive characteristics
• Normal and relieving temperatures
• Body, trim, sealing and connection material requirements
• For HTB evaluation, bellows compatibility and service limitations

Connections and Installation

Confirm the mechanical interfaces and installation constraints before finalizing the valve specification.

• Inlet and outlet connection type and size
• Required pressure class or rating
• Available installation space and orientation
• Inlet pressure loss and discharge piping considerations

Compliance and Verification

The final selection must be checked against the applicable project requirements and supported by the required technical documentation.

• Applicable design code and jurisdictional requirements
• Certified capacity and sizing documentation, where required
• Material and inspection documentation
• Manufacturer data sheet, drawings and maintenance requirements

Pressure Vessels and Process Equipment

Pressure vessels and process equipment may require overpressure protection where blocked outlets, control failures or other credible process deviations can cause pressure to rise beyond the permitted limit.

• Process vessels and pressurized equipment
• Process skids and packaged equipment
• Equipment exposed to multiple pressure sources
• Installations requiring a defined relief discharge route

Oil, Gas and Petrochemical Facilities

Process units in oil, gas and petrochemical facilities can experience overpressure due to equipment isolation, pressure-control failure, thermal effects or abnormal operating conditions.

• Process and utility equipment
• Pressurized vessels and associated systems
• Equipment connected to common discharge headers
• Applications where backpressure must be assessed

Thermal and Utility Systems

Pressurized liquid and gas systems within industrial utility installations require assessment of credible pressure-rise scenarios, including thermal expansion where liquid can become trapped between isolation points.

• Pressurized utility circuits
• Thermal fluid and liquid service, where suitable
• Isolated sections exposed to temperature changes
• Equipment with defined maximum allowable pressure

Chemical and Specialty Process Plants

Chemical service requires careful evaluation of fluid properties, temperature, corrosion mechanisms, sealing materials and the consequences of relief discharge.

• Pressurized process equipment
• Service involving corrosive or chemically active media
• Systems with specific material compatibility requirements
• Applications requiring a reviewed discharge arrangement

Industrial Manufacturing and Plant Utilities

Manufacturing facilities use pressurized systems for process operations and plant utilities. Relief protection must be evaluated against the equipment design basis and the consequences of a pressure excursion.

• Pressurized process and service equipment
• Industrial utility systems
• Equipment with pressure-reducing or control devices
• Systems requiring defined inspection and maintenance access

Installations with Backpressure Constraints

Where relief valves discharge into a common header or a pressurized collection system, outlet pressure conditions become an important part of valve selection.

• Common discharge headers
• Discharge systems with variable pressure
• Installations where built-up backpressure must be calculated
• Applications requiring evaluation of a balanced-bellows design

Scenario A — Conventional Relief Arrangement

A protected item of equipment requires overpressure protection, and the discharge-system conditions are compatible with the verified operating limits of a conventional valve.

Engineering review: Confirm the relief case, required capacity, set pressure, outlet conditions and the manufacturer’s allowable limits before specifying an HTO valve.

Scenario B — Backpressure Requires Further Evaluation

A valve discharges into a header where superimposed or built-up backpressure may influence valve operation.

Engineering review: Quantify the backpressure conditions and evaluate whether an HTB balanced-bellows configuration is suitable for the service.

Scenario C — Trapped Liquid Exposed to Heating

Liquid trapped between closed isolation points can expand as its temperature rises, potentially creating excessive pressure in the isolated section.

Engineering review: Determine whether dedicated thermal relief protection is required and verify that the selected valve is suitable for the liquid service and required relieving duty.

New Valve Applications

For a new installation, provide the process design basis and required relief conditions so the valve configuration and sizing can be evaluated against the application.

• Protected equipment and process service
• Set pressure and design pressure
• Required relieving capacity or sizing calculation
• Operating and relieving temperatures
• Inlet and outlet connection requirements

Conventional vs Balanced-Bellows

Where discharge backpressure may affect valve performance, the pressure conditions should be established before selecting between HTO and HTB designs.

• Superimposed backpressure
• Estimated or calculated built-up backpressure
• Common discharge header conditions
• Process medium and bellows compatibility, where applicable
• Manufacturer-confirmed design limitations

Existing Valve Assessment

For replacement or technical review, existing equipment data can help establish the current configuration and identify information that requires verification.

• Existing valve nameplate and model information
• Manufacturer data sheet and drawings
• Set pressure and rated capacity, where documented
• Known operating or maintenance issues
• Changes to process conditions or discharge piping

Process Data

• Fluid name, composition and phase
• Normal operating pressure and temperature
• Required set pressure
• Required relieving pressure and temperature
• Governing overpressure scenario
• Required capacity or available sizing calculation

Mechanical Data

• Inlet and outlet sizes and connection types
• Required pressure class or rating
• Body and trim material requirements, if specified
• Installation constraints and orientation
• Applicable project specifications and design code

Discharge-System Data

• Discharge to atmosphere or closed system
• Superimposed backpressure, if known
• Built-up backpressure, if calculated
• Discharge header operating conditions
• Relevant inlet and outlet piping information