Share This Post

Share on facebook
Share on linkedin
Share on twitter
Share on email
Share on whatsapp
Share on telegram

Welding Consumables Used for LNG Tanks

By: Dr. Eng. Pablo Ozaeta L.


The 9%Ni steels could be welded using filler metals with similar chemical composition if the appropriate heat-treatment is applied to match the mechanical properties of the base metal. Filler metals having 12% nickel have also been developed, showing good toughness but low ductility. Welds made with this consumable have shown good results in the laboratory test, but have not been accepted for the construction of large vessels.

Fig 1-2: SAW process on horizontal joint

For LNG Tank construction, these solutions are not viable. Therefore, high nickel austenitic consumables are used. Nickel base alloys are chosen due their good strength, good toughness at -196°C and because its thermal expansion coefficient is very close to 9%Ni steel, thereby reducing the thermal stress during tank operation.

1.    Welding Consumables:

For the SAW welding process, there are different types of wires based on NiMo and NiCrMo alloys. In Europe and USA, AWS A5.14 ER-NiCrMo-3 or AWS A5.14 ER- NiCrMo -4 are commonly used.

The AWS A5.14 ER NiCrMo-3 is an Inconel 625 type alloy, which increases its mechanical strength by the formation of secondary solidification constituent. Due to its chemical composition Gamma prime, Delta and Mu secondary solidification constituent, and carbides MC, M6C and M23C6 are stable in the solid phase, but the thermo-mechanical treatment will define the final phases distribution.

Undiluted weld metal tensile tested has an UTS around 760 MPa, yield strength around 510 MPa and elongation around 46%, making it the ideal consumable to be used for this application. But its high hot cracking sensitivity makes it so that many tanks’ constructors reject the idea of using it. However, it should be noted that using the proper flux and right welding parameters, it’s a possible and reliable way to get sound welds with highest mechanical properties.

The AWS A5.14 ER NiCrMo-4 is a Hastalloy C-276 alloy type, which increases its strength by solid solution. Only M6C rich molybdenum carbides and Mu secondary solidification constituent are stable in the solid phase. Undiluted weld metal tensile tested has an UTS around 690 MPa, yield strength over 400 MPa and elongation around 35%, making it an acceptable consumable to be used for this application, especially due to its lower hot crack sensitivity.

Due to that mechanical strength of this alloy system is controlled by solid solution mechanism, dilution with base metal should have an important role on tested strength by cylindrical all weld metal tension test, where the place where the sample was obtained could have an important effect.

This is one of the hypotheses in this dissertation, attempting to compare its effect against other typical welding variables. Using X-ray fluorescence technique, main alloy elements will be determined on each tensile tested sample and will be statistically correlated with other parameter.

More To Explore

Tank Inspection In-Service Condition: The Acoustic Emission (AE)

Petroleum tanks used to store crude oil, aviation fuel, gasoline, diesel and other products above and below ground. Leaking tanks may create significant environmental damage and jeopardize safety. Soil and water contamination can be tremendous and be undetected for years.

Different methods have been developed and applied during the recent decades for non-destructive evaluation of metal and fiber-reinforced plastics (FRP) structures. Among these methods, acoustic emission technology is unique as it not only detects flaws but also is used for on-line, real-time monitoring of structural integrity without interruption of operation, cleaning, or product evacuation.

Read More »

Recommissioning Tanks: What Role Does NDT Play? (Part 2)

The oil and gas industry experienced some major challenges in 2020. With the sudden reduction in fuel consumption, there was a substantial global surplus of crude oil. This unique situation has seen storage facilities reach maximum capacity and even crude tankers being used to store unwanted product.

Retired storage facilities are being targeted for reinstatement, and operators are considering tank construction to increase capacity. With increased storage requirements and potential inspection deferrals, there is also an increased requirement to perform in-service tank inspection to assess critical components within the asset.

This article will do a complete NDT techniques revision that can be applied to the recommissioning tanks.

Read More »