Understanding PWHT for Vessels, Storage Tanks, and Spiral Tanks
Post Weld Heat Treatment (PWHT) is a critical process in the fabrication of pressure vessels, storage tanks, and spiral tanks to relieve residual stresses, enhance mechanical properties, and improve metallurgical stability. These structures often operate under high pressure, extreme temperatures, and corrosive environments, making PWHT essential for long-term performance and safety.
PWHT Tech India specializes in providing ASME-compliant PWHT solutions, ensuring that your tanks and vessels meet industry standards for durability and operational efficiency.
ASME Standards for PWHT in Tanks and Vessels
The American Society of Mechanical Engineers (ASME) outlines strict requirements for PWHT based on material type, thickness, and operational conditions. The most relevant standards include:
ASME Section VIII, Division 1 & 2 – Governs the construction and PWHT requirements of pressure vessels.
ASME B31.3 – Specifies heat treatment for piping systems, often associated with tanks and vessels.
ASME Section IX – Covers welding and heat treatment procedures.
ASME B31.1 – Specifies heat treatment for power plant and industrial piping, often linked to storage tank networks.
These standards dictate the temperature range, soaking time, heating/cooling rates, and cooling methods necessary to achieve structural integrity and compliance.
Recommended PWHT Processes for Tanks and Vessels
PWHT Tech India provides various heat treatment methods tailored to vessels, storage tanks, and spiral tanks, ensuring compliance with ASME standards:
1. Furnace PWHT
Ideal for small to medium-sized vessels and tanks.
Performed in large industrial furnaces with controlled temperature cycles.
Ensures uniform heat distribution and precise process control.
2. Localized PWHT (Resistance Heating)
Applied to specific welded areas of large tanks and vessels.
Uses ceramic pad heaters or electrical resistance blankets for controlled heating.
Suitable for field-based PWHT where entire furnace heating is not feasible.
3. Induction Heating PWHT
Uses electromagnetic induction for quick and efficient heating.
Offers precise temperature control, reducing the risk of overheating or thermal distortion.
Commonly used for large storage tanks and spiral tanks that cannot be moved to a furnace.
4. Oil & Gas Firing Method for PWHT
Used for oversized vessels and large storage tanks where electrical methods are not practical.
Oil-firing and gas-firing systems generate the necessary heat for stress relieving and annealing.
PWHT Tech India’s Fire Wave System ensures uniform heat distribution, optimized fuel efficiency, and controlled temperature profiles.
The Role of Oil & Gas Firing in PWHT Processes
For large-scale industrial heat treatment, oil and gas firing methods offer a reliable solution:
Oil-Fired PWHT
Uses high-efficiency burners to generate uniform heat.
Suitable for field applications where electrical power is limited.
Provides deep penetration heat treatment for thick-walled tanks and vessels.
Gas-Fired PWHT
Utilizes natural gas or propane as the heat source.
Ensures clean combustion, reducing contamination risks.
Ideal for remote oil and gas installations requiring on-site PWHT.
PWHT Tech India’s Fire Wave System is engineered to provide precise temperature control, fuel efficiency, and compliance with ASME, API, and other global industry standards.
How PWHT Tech India Supports Your PWHT Needs
At PWHT Tech India, we provide end-to-end PWHT services for vessels, storage tanks, and spiral tanks, ensuring structural integrity, compliance, and longevity. Our expertise includes:
Custom-designed furnaces for large vessels and tanks.
On-site and field PWHT solutions using resistance, induction, and gas/oil-fired methods.
ASME-compliant heat treatment procedures tailored to specific material and design requirements.
Quality assurance and documentation to meet industry regulations and certification requirements.
Deep Dive into PWHT for Vessels, Storage Tanks, and Spiral Tanks
Post Weld Heat Treatment (PWHT) is a critical process in the fabrication and maintenance of large industrial structures, especially in sectors like oil & gas, petrochemicals, power plants, and heavy engineering. Vessels, storage tanks, and spiral tanks are designed to withstand high pressures, extreme temperatures, and corrosive environments, making proper heat treatment essential for long-term durability and safety.
PWHT Tech India offers a comprehensive range of PWHT solutions tailored to industry standards such as ASME, API, and AWS, ensuring that our clients receive high-quality, compliant, and cost-effective heat treatment services.
The Importance of PWHT in Tanks and Vessels
1. Why is PWHT Necessary?
Welding introduces residual stresses and microstructural changes in metals, which can lead to:
Stress corrosion cracking (SCC) – Especially in pressure vessels and storage tanks handling chemicals or high-pressure fluids.
Brittle fracture – Caused by high residual stresses, particularly in thick-walled vessels.
Hydrogen-induced cracking (HIC) – Common in oil & gas applications, where hydrogen diffusion can weaken the material.
Distortion and warping – Large storage tanks and spiral tanks can experience shape deformation if not properly heat-treated.
PWHT eliminates these issues by reducing residual stresses, refining grain structure, and enhancing toughness, thereby improving the overall integrity of the vessel or tank.
ASME Guidelines for PWHT in Vessels and Tanks
The ASME Boiler and Pressure Vessel Code (BPVC) Section VIII and ASME B31.3 Process Piping Code define the following PWHT parameters:
Temperature Range – Typically between 600°C and 750°C (1100°F–1380°F), depending on material and thickness.
Soaking Time – Minimum of 1 hour per inch of thickness, ensuring uniform stress relief.
Controlled Heating and Cooling – Maximum heating/cooling rates to prevent material cracking or structural damage.
Documentation and Quality Assurance – Strict requirements for process validation, temperature monitoring, and compliance reporting.
PWHT Tech India ensures full compliance with ASME, API, and client-specific specifications, delivering certified, high-precision heat treatment.
PWHT Methods for Vessels, Storage Tanks, and Spiral Tanks
1. Furnace PWHT
Used for small to medium-sized pressure vessels and tanks.
Performed in a controlled atmosphere, ensuring even heating and precise thermal control.
Ideal for batch processing of multiple components in a single cycle.
2. Localized PWHT (Resistance Heating)
Used for large tanks, pipelines, and site-installed vessels where full furnace heating is impractical.
Ceramic pad heaters or resistance blankets are applied to welded joints for targeted stress relief.
Monitored with thermocouples and digital controllers to ensure precise temperature control.
3. Induction Heating PWHT
Utilizes electromagnetic induction to heat specific areas quickly and efficiently.
Reduces cycle time while maintaining consistent heat distribution.
Ideal for on-site PWHT of large vessels and spiral tanks.
4. Oil & Gas Firing PWHT (Fire Wave System)
Used for large-scale heat treatment in oil refineries, petrochemical plants, and offshore projects.
Oil-fired and gas-fired burners generate the required temperature with efficient heat transfer and minimal fuel waste.
PWHT Tech India’s Fire Wave System ensures uniform heating, controlled temperature gradients, and compliance with ASME standards.
How Oil & Gas Firing PWHT Works
1. Oil-Fired PWHT
Uses high-efficiency burners that run on diesel, heavy fuel oil (HFO), or other industrial oils.
Ideal for remote sites where electricity is limited or costly.
Provides deep penetration heating, ensuring stress relief for thick-walled storage tanks and pressure vessels.
2. Gas-Fired PWHT
Uses natural gas or propane as the heat source.
Produces clean combustion with low emissions, making it an environmentally friendly option.
Common in oil refineries, LNG plants, and offshore applications.
Both methods are cost-effective alternatives to electric furnaces for on-site PWHT of large industrial structures.
PWHT Tech India’s Expertise in Large-Scale Heat Treatment
At PWHT Tech India, we provide end-to-end PWHT services, ensuring high-quality heat treatment for tanks, vessels, and industrial equipment. Our capabilities include:
✔ Custom-built oversized furnaces for large vessels and tanks.
✔ On-site PWHT solutions using resistance, induction, and gas/oil-fired methods.
✔ ASME-certified heat treatment procedures tailored to specific materials and applications.
✔ Comprehensive QA/QC documentation to meet global regulatory standards.
✔ 24/7 technical support and mobile PWHT units for field projects.
With our state-of-the-art FireWave System, we deliver high-precision, cost-effective, and compliant PWHT solutions that maximize safety, reliability, and performance.
Conclusion
Ensuring the proper PWHT of vessels, storage tanks, and spiral tanks is crucial for safety, performance, and regulatory compliance. With PWHT Tech India’s expertise and advanced FireWave oil & gas firing systems, we deliver reliable and cost-effective heat treatment solutions that meet ASME standards and industry expectations.
Contact PWHT Tech India today to discuss how we can support your PWHT requirements with our cutting-edge solutions!
Final Thoughts :
PWHT is an essential process in the fabrication and maintenance of vessels, storage tanks, and spiral tanks, ensuring long-term structural integrity and compliance with ASME standards. Whether you require furnace-based, resistance heating, induction, or oil/gas-fired PWHT, PWHT Tech India is your trusted partner in delivering world-class heat treatment solutions.
For expert consultation and services, contact PWHT Tech India today!