When Are Deaerators Required in Pressure Systems?

Deaerators are required in steam boiler systems and hot-water heating applications when dissolved oxygen and carbon dioxide must be removed from feedwater to prevent corrosion, pitting, and premature equipment failure. They are mandated by system design standards, boiler codes, and plant operating requirements, and the deaerator pressure vessel must be built to ASME Section VIII when operating above defined pressure thresholds.

Key Takeaways

• Deaerators are required in high-pressure steam systems, continuous makeup water applications, power generation plants, and process facilities where dissolved oxygen corrosion risk is significant.
• The ASME Boiler and Pressure Vessel Code (BPVC) Section VIII governs deaerator storage vessel fabrication. Fabricators must hold the ASME U Stamp to manufacture code-compliant vessels.
• HEI Standards govern deaerator performance specifications including oxygen removal efficiency and venting capacity.
• Signs a system needs a deaerator include persistent corrosion, high feedwater oxygen readings above 7 parts per billion, and significant makeup water volume being added continuously.
• Deaerators are sized based on boiler feedwater flow rate, condensate return percentage, and steam load requirements.
• Choosing an ASME U Stamp and NBBI R Stamp certified fabricator ensures the deaerator pressure vessel is code-compliant, insurable, and documented for National Board registration.

What Is a Deaerator and What Does It Do?

A deaerator is a pressure vessel designed to remove dissolved gases, primarily oxygen and carbon dioxide, from boiler feedwater before that water enters the boiler. Dissolved oxygen is the leading cause of corrosion and pitting in boiler tubes, feedwater lines, and heat exchangers. Carbon dioxide forms carbonic acid in condensate return systems, accelerating pipe degradation.

How a Deaerator Removes Dissolved Oxygen

Deaerators work by heating the feedwater to the saturation temperature of the steam being injected, which drives dissolved gases out of solution. The gases are then vented continuously to atmosphere through a vent condenser. The result is feedwater with dissolved oxygen reduced to below seven parts per billion (ppb), the industry standard threshold for corrosion control in most steam systems.

Tray-Type vs. Spray-Type Deaerators

Tray-type deaerators cascade feedwater over multiple stainless steel trays through a steam environment, increasing the surface area exposed to the stripping action. Spray-type deaerators atomize feedwater into fine droplets before mixing with steam, achieving rapid heating and degassing in a single deaerator pressure vessel. Both types are typically rated for pressures between 5 psig and 15 psig, though higher-pressure versions serve large utility and industrial applications. See Red River’s pressure vessel fabrication scope for how deaerator storage vessels are fabricated across both design types.

When Are Deaerators Legally or Operationally Required?

Deaerators are not mandated by a single federal law, but they become required under a combination of technical necessity, code compliance, and engineering specification in several defined scenarios.

High-Pressure Steam Boiler Systems

ASME BPVC Section I governs power boilers, and most engineering standards for systems operating above 15 psig steam pressure treat deaeration as a design requirement rather than an option. At these pressures, dissolved oxygen causes accelerated corrosion that is not manageable through chemical treatment alone. System designers and mechanical engineers routinely specify deaerators as mandatory components in power generation plants, industrial process facilities, and large commercial heating systems.

Continuous Feedwater Supply Systems

Any boiler system with continuous makeup water requirements, drawing fresh water regularly rather than operating on a closed loop, requires deaeration. Fresh water carries significantly more dissolved oxygen than recirculated condensate. Without a deaerator, chemical oxygen scavengers such as sodium sulfite or hydrazine become inadequate as the sole corrosion control method at scale.

Utility and Combined Heat and Power Applications

Power generation facilities and combined heat and power (CHP) plants operating at elevated steam pressures and temperatures always include deaerators in the system design. ASME and the Heat Exchange Institute (HEI) both publish standards that guide deaerator sizing and performance in these applications. These standards function as design mandates in any facility with a licensed boiler operator and a formal inspection regime.

Process Plants With High-Temperature Feedwater Requirements

In oil and gas, chemical processing, and refining applications, feedwater entering process boilers or heat recovery steam generators (HRSGs) must meet strict dissolved gas specifications. Plant engineering standards and equipment manufacturer requirements specify deaeration at the design stage. In this context, the deaerator pressure vessel is a contractual and technical requirement, not a recommendation. Red River’s prefabrication services cover deaerator storage vessels built to stamped engineering drawings for integration into existing feedwater systems.

Insurance, Warranty, and OEM Mandates

Many boiler manufacturers void warranties if a deaerator is not installed when the system design requires one. Industrial insurance providers underwriting boiler and pressure vessel coverage may require deaeration as a loss-prevention measure in high-pressure steam applications. The combination of OEM requirements and insurance conditions makes deaeration effectively mandatory for large systems even when no single code provision explicitly compels it.

What Standards Govern Deaerator Design and Fabrication?

Because deaerators operate under pressure and handle high-temperature feedwater, they fall under the jurisdiction of the ASME Boiler and Pressure Vessel Code.

ASME BPVC Section VIII and Section I

ASME BPVC Section VIII, Division 1 covers pressure vessels, including the deaerator storage tank, which is typically a horizontal deaerator pressure vessel operating at the deaerator’s working pressure. ASME BPVC Section I applies to power boilers and informs the feedwater quality specifications that make deaeration necessary.

HEI Standards for Deaerators

HEI Standards for Deaerators are published by the Heat Exchange Institute and cover venting capacity, oxygen removal efficiency, and materials for spray and tray-type deaerators. These standards define the performance specifications that a code-compliant deaerator must meet in industrial service.

ASME U Stamp Fabrication Requirement

Fabricators producing deaerator storage vessels for systems operating above the ASME exemption thresholds, generally above 15 psig and above six inches in diameter, must hold an ASME U Stamp certification. This means the fabricator is authorized by ASME to manufacture pressure vessels in compliance with BPVC Section VIII and is subject to third-party inspection by an ASME Authorized Inspector. Vessels must be registered with the National Board of Boiler and Pressure Vessel Inspectors after fabrication.

Red River holds active ASME U Stamp (U4) and NBBI R Stamp certifications, both verifiable directly with the issuing bodies. Every deaerator pressure vessel Red River fabricates is inspected by an ASME Authorized Inspector and delivered with full material test reports (MTRs) and quality control documentation. See Red River’s capabilities for how documentation and ASME certification are managed across deaerator vessel scopes.

What Are the Signs a System Needs a Deaerator?

Not every steam system includes a deaerator from initial commissioning. Engineers and plant operators sometimes identify the need during operation.

Operational Indicators

Common signs that a deaerator is required include recurring pitting or corrosion in boiler tubes, feedlines, or heat exchanger surfaces despite chemical treatment, high oxygen readings above 7 ppb in feedwater quality testing, elevated iron or copper content in feedwater indicating corrosion product carryover, and significant continuous makeup water volume indicating low condensate return and high dissolved-oxygen-rich fresh water input.

When Chemical Treatment Is No Longer Sufficient

Boiler manufacturer recommendations following a warranty review, and insurance underwriter requirements following a loss event or risk assessment, are additional indicators. Chemical oxygen scavenging can supplement deaeration but cannot replace it in systems where corrosion risk is significant and continuous.

How Does Deaerator Sizing Work?

Deaerators are sized based on the maximum feedwater flow rate the system requires, expressed in pounds per hour or gallons per minute. The deaerator storage capacity is typically sized to provide five to ten minutes of boiler feedwater storage at full load.

Sizing Inputs for a Deaerator Pressure Vessel

Key sizing inputs include boiler horsepower (BHP) or maximum steam output, condensate return percentage (higher return reduces makeup water and oxygen load), feedwater temperature entering the deaerator, required discharge temperature and pressure, and makeup water quality (municipal, well, or treated water each carry different dissolved gas loads). A mechanical engineer or system designer specifies these parameters. When the storage vessel is fabricated as an ASME pressure vessel, which is required for most industrial applications, the fabricator works from stamped engineering drawings reviewed by an ASME Authorized Inspector. See Red River’s modular skid packages for how deaerator vessels are integrated into complete feedwater system assemblies.

Why Does the Fabricator Matter for Deaerator Vessels?

The deaerator storage vessel operates continuously under heat and pressure, feeding one of the most critical pieces of equipment in a facility. Fabrication quality directly affects system reliability, safety, and service life.

ASME U Stamp as the Baseline Requirement

A fabricator holding the ASME U Stamp is authorized to manufacture the deaerator pressure vessel to the code standard required by law, insurance, and OEM specifications. Non-certified fabricators cannot legally stamp a pressure vessel for ASME applications, and vessels produced without the stamp cannot be registered with the NBBI. Learn more about Red River’s history and certifications at Red River’s about page.

What Red River Delivers on Every Deaerator Vessel

Red River has fabricated ASME-certified pressure vessels from Gillette, Wyoming, since 2003. Every deaerator pressure vessel leaves the facility with a U Stamp data report, full MTR documentation, and an ASME Authorized Inspector approval.

What This Means When Specifying a Deaerator

Deaerators are required by a combination of code, OEM mandates, and operational necessity rather than by a single blanket rule. The conditions that trigger the requirement, including operating pressure, makeup water volume, and dissolved oxygen targets, determine both the deaerator design and the fabrication standard the storage vessel must meet.

Getting the specification right at the design stage, including ASME Section VIII compliance, HEI performance standards, and correct storage sizing, avoids the corrosion damage, warranty voidance, and regulatory complications that follow from a system without adequate feedwater deaeration.

Discuss Your Deaerator Vessel Requirements With Red River

Red River fabricates ASME-certified deaerator storage vessels for boiler feedwater and process applications across oil and gas, power generation, and industrial sectors from Gillette, Wyoming, since 2003. Red River holds active ASME U Stamp and NBBI R Stamp certifications and is an American Welding Society (AWS) member. Request a quote or call 1-307-257-5332 to discuss your deaerator vessel design pressure, storage sizing, and fabrication scope.

Frequently Asked Questions

1. What Dissolved Oxygen Level Requires a Deaerator?

Industry standards require dissolved oxygen in boiler feedwater to be reduced to seven parts per billion (ppb) or below. In most high-pressure steam systems, this level can only be reliably achieved through mechanical deaeration, as chemical treatment alone is insufficient at scale.

2. Do Low-Pressure Steam Systems Require a Deaerator?

Low-pressure systems below 15 psig may not require a deaerator by code, but they may still benefit from one. Systems with high makeup water volume, persistent corrosion issues, or manufacturer requirements should be evaluated by a mechanical engineer to determine whether deaeration is warranted regardless of operating pressure.

3. Does a Deaerator Need to Be ASME-Certified?

The deaerator storage vessel, the horizontal deaerator pressure vessel that holds degassed feedwater, must be fabricated to ASME BPVC Section VIII by a U Stamp certified fabricator when it operates above the code exemption thresholds. The deaerator head or heating section may have additional code requirements depending on design and operating pressure.

4. How Long Do Deaerators Last?

A properly fabricated and maintained deaerator storage vessel can operate for 30 years or more. Service life depends on water quality, operating pressure and temperature cycles, and the quality of the original fabrication. Documented corrosion of the vessel itself is usually traced to water quality issues within the deaerator or improper commissioning.

• 5. Can Red River Fabricate Deaerator Storage Vessels?

Yes. Red River fabricates ASME Section VIII deaerator pressure vessels for boiler feedwater systems. Every vessel is built under Red River’s ASME U Stamp (U4) certification, inspected by an ASME Authorized Inspector, and delivered with full MTR and quality control documentation. Request a quote or call 1-307-257-5332 to discuss your project.