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Jul 10, 2020

Choosing Filler Metals to Weld ASTM A516 Gr 70 Pressure Vessels

In pressure vessel fabrication, ASTM A516 Grade 70 carbon steel plate (A516 Gr 70) is the predominant material for several reasons.

-It offers strength and toughness at low service temperatures.
-It provides appealing weldability.
-It is readily available commercially.

The material is typically produced in thicknesses ranging from 1/4 inch to 1-1/2 inches. Anythickness above 1-1/2 inch requires the material be normalized to ensure its toughness during use.

Environmental shot of large pressure vessel on a trailer
Photo credit: Doug Pillow - Owner/CEO of CDP Sales,
Porter TX

Despite A516 Gr 70 being relatively easy to weld, welding operators must be ASME-certified to weld pressure vessels, and it’s critical to have the right filler metal to meet the material’s mechanical properties. That can be a challenge since pressure vessel designs are subject to strict temperature requirements. The filler metal must produce welds that meet specific impact toughness at low temperatures.

In addition, filler metals must meet the chemical properties outlined by ASME Boiler and Pressure Vessel Code, Section IX.

So how do pressure vessel fabricators make the right filler metal choice? By answering a few key questions.

1. What is the tensile strength and yield strength of the material? A516 Gr 70 has tensile strengths ranging from 70 to 90 ksi, so the filler metals for root, fill and cap passes need to offer compatible mechanical properties.

2. What are the Charpy V-notch (CVN) requirements at a particular temperature (Fahrenheit)?Typically, A516 Gr 70 plate requires a filler metal that can offer an average impact toughness greater than 20 ft-lb at -20 degrees Fahrenheit or greater than 20 ft-lb at -50 degrees Fahrenheit.

3. Will the weld be placed in service in the as-welded condition or stress relieved?
Stress relieving for A516 Gr 70 is approximately 1,150 degrees Fahrenheit, with the plate usually being held at that temperature for one hour per inch of material thickness. If this process is necessary, the chosen filler metal must be formulated for stress relieving and the welds it produces able to withstand these high temperatures.

4. Is it necessary to qualify procedures based on individual lots of filler metals?
If this is required, pressure vessel fabricators should maintain close communication with their filler metal manufacturer to ensure reasonable lead times and ample inventory for the project.

5. Are actual certificates or certificates of conformance needed for the filler metal?
Actual certificates or Certified Material Test Reports (CMTR) provide the actual mechanical properties of the filler metal based on lot testing. If these are needed, pressure vessel fabricators should select a filler metal that holds that certificate and meets their toughness requirements or provide lead times to the manufacturer to complete the appropriate testing. Certificates of conformance are generally available on a filler metal manufacturer’s website.

Welding processes and filler metals
Pressure vessel fabricators can weld A516 Gr 70 with several processes and filler metal types, depending on the design and the required mechanical properties. For example:

-Solid and metal-cored wires: American Welding Society (AWS) ER70S-6 wires can be used for the root pass with an AWS E70C-6M H4 metal-cored wire for the fill and cap passes.

-Gas-shielded flux-cored wires (FCAW-G): An AWS E71T-12MJ H4 wire and other T-12 wires are options for pressure vessel fabrication. These wires offer good impact toughness and lower levels of manganese.

Submerged arc welding can be used for the fill and cap passes. Appropriate filler metals and fluxes vary depending on the job’s mechanical property needs.

As with any application, it is critical that pressure vessel fabricators follow the filler metal manufacturer’s recommendations for amperage, voltage and travel speed for the chosen wire diameter to gain the best results.

For more information about filler metals for pressure vessel welding, contact the Hobart applications department at 800-532-2618.