Pressure vessels operate in environments where margins for error are extremely small. Designed to contain gases or liquids at pressures far beyond ambient conditions, they rely on both material integrity and fabrication quality to maintain structural integrity and containment throughout their service life. The ASME Boiler and Pressure Vessel Code provides the framework that governs the reliability of pressure vessels but real-world performance is defined during welding. Steels such as ASME SA516 and ASME SA285 are widely used for pressure vessel construction, each selected for specific service demands. Both ASME SA516 and ASME SA285 react differently to welding, requiring welding practices that reflect their respective strength levels, toughness requirements, and susceptibility to heat input and hydrogen.
ASME SA516
ASME SA516 is a fine-grain, fully killed carbon steel developed for pressure vessel service where strength, toughness, and resistance to brittle fracture are essential to long-term pressure vessel performance. It is intended for moderate to lower operating temperature applications, where resistance to brittle fracture is a key design requirement. Supplied in four strength grades, Grade 55, Grade 60, Grade 65, and Grade 70, ASME SA516 allows designers to select the appropriate strength level to suit vessel thickness, pressure requirements, and overall design constraints, while maintaining consistent mechanical properties. The steel is applied to industrial boilers, chemical reactors, and pressure vessels across oil, gas, and petrochemical facilities, as well as storage vessels for compressed gases and other low-temperature pressure applications like liquefied petroleum gas vessels and refrigerated process equipment.
Welding Best Practices for ASME SA516 Pressure Vessels
Heat Input Control
Successful welding of ASME SA516 pressure vessels starts with well-regulated heat input control. Moderate, stable welding parameters should be used throughout, avoiding high amperage and wide weave beads that introduce unnecessary heat. Consistent interpass temperatures are equally important, particularly when welding thicker plate sections, as cumulative overheating can reduce toughness in the heat-affected zone.
Preheating Practice
Preheating should be applied where ASME SA516 plate thickness, restraint, or Carbon Equivalent indicate an increased cracking risk. The objective is uniform heat across the ASME SA516 pressure vessel joint area, rather than localised warming at the weld line. Maintaining preheat between welding passes helps control cooling rates and supports more predictable weld metal behaviour during solidification.
Consumable Handling
When welding ASME SA516 pressure vessels, controlling hydrogen is vital to protect toughness and prevent hydrogen-assisted cracking in pressure retaining joints. For this reason, low-hydrogen consumables such as E7018 electrodes should be standard practice for ASME SA516 welding. These consumables must be handled carefully by storing them in heated ovens and issuing them in a controlled manner to limit moisture exposure during fabrication. Any electrodes showing signs of contamination should be removed from service. Moreover, filler metals should be selected to match the specified ASME SA516 grade, ensuring consistent strength and mechanical properties across the welded joint.
Post-Weld Heat Treatment
Post-weld heat treatment (PWHT) should be planned and applied in line with code requirements, plate thickness, and service conditions for ASME SA516 pressure vessels, rather than treated as an automated step. When required, PWHT must be carried out using controlled heating and cooling rates to avoid introducing new thermal stresses. Properly applied, it relieves residual welding stresses and tempers hardened regions in the heat-affected zone, improving fracture resistance and supporting reliable long-term pressure vessel service.
ASME SA285
ASME SA285 is a carbon steel plate used for fusion-welded pressure vessels operating at low to intermediate pressure levels. Compared with ASME SA516, it offers lower tensile strength but higher ductility and formability, which simplifies rolling and forming during fabrication. Its lower carbon content also contributes to good weldability and predictable behaviour during welding. Supplied in Grades A, B, and C according to strength requirements, ASME SA285 is found in stationary storage tanks, low-pressure boiler components, and general industrial pressure vessels operating under stable service conditions.
Welding Best Practices for ASME SA285 Pressure Vessels
Surface Preparation
Good welding practice for ASME SA285 pressure vessels begins with thorough surface preparation. Mill scale, rust, oil, and other contaminants should be removed from joint areas before welding starts. Clean joint faces promote proper fusion and reduce the likelihood of inclusions or lack-of-fusion defects in pressure-retaining welds.
Weldability Control
ASME SA285 benefits from lower carbon content, which improves weldability and reduces the risk of brittle microstructures forming during cooling. In most cases, preheating is not required. However, thicker plates or highly restrained joints should still be assessed carefully, as controlled preheat can help manage cooling rates and minimise residual stress.
Electrode Selection
When welding ASME SA285 pressure vessels, filler metals should be selected to match the mechanical properties of the base material rather than exceeding them. For many pressure vessel applications, E6010 electrodes are used for root passes to achieve reliable penetration, followed by E7018 electrodes for fill and cap passes. This approach supports consistent strength and sound weld profiles.
Joint and Edge Preparation
Proper joint preparation is critical for achieving full penetration in ASME SA285 pressure vessels. Bevel designs such as V-groove or U-groove should be chosen based on plate thickness and joint configuration. Moreover, accurate fit-up and controlled root gaps help ensure welds meet inspection and certification requirements.
Procedure Control
Although ASME SA285 pressure vessel steel has lower strength than higher-grade alternatives, welding procedures should still be qualified and carefully controlled. Managing welding sequence, heat input, and join restraint helps limit distortion and residual stress, particularly in large-diameter pressure vessels and storage tanks where dimensional accuracy is vital.
Ensuring Quality with Masteel UK
Masteel UK is a specialist supplier of ASME-certified pressure vessel plate, providing fully traceable ASME SA516 and ASME SA285 materials in line with international fabrication standards. By working with engineers and fabricators early in the project lifecycle, we ensure material selection aligns with welding requirements, code compliance, and long-term service conditions. For support in selecting the right pressure vessel steel, contact our team now.