WP-301 Welding of Zirconium and its Alloys

WP 301 Zirconium alloy welded WEB

Zirconium and its principal alloy zircaloy possess physical properties unmatched by most other metallic materials. The combination of mechanical strength, corrosion resistance and their high temperature stability make them attractive for use in sectors as diverse as biochemical, nuclear, aerospace and petrochemicals.

More specifically, zircalloy is used in the manufacture of pressure vessels and heat exchangers. The alloy has excellent resistance to most organic and inorganic acids, salt solutions, strong alkalis, and some molten salts and these properties makes it suitable for use in pumps where strength coupled with corrosion resistance is mandatory. Zirconium alloys are biocompatible, and therefore can be used for body implants: a Zr-2.5Nb alloy is used in knee and hip implants.

By far the most significant applications however are in nuclear power plant. Zirconium alloys are widely used in the manufacture of fuel rods especially in pressurised water reactors 1.

Figure 1. Zirconium alloy welded with effective inert gas protection showing no discolouration.

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WP-291 Clarification over Tungsten Electrodes for TIG/GTAW Welding

HFT Profile Welding

The tungsten arc welding concept, originally introduced as a practical tool in 1950, is now established as the most versatile technique for producing fusion welds to the highest quality standards.

A temperature of around 4,000ºC is generated in the arc during welding and the role played by the electrode is therefore crucial. It must have a high melting point and it must be non-consumable: tungsten quickly established itself as the most suitable material.

As the knowledge of arc characteristics increased however it became clear that the use of pure tungsten presented some limitations on process development, particularly arc starting, stability and electrode wear.

Early research showed that the addition of thoria resulted in overall improvements in performance and from this work a range of tungsten electrodes containing oxide additions or ‘dopants’ were introduced progressively.

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WP-269 Shielding Gas and Purging Techniques during Welding-Part 4

HFT Weld Arc Large Pipe Purple PHO 05B

Part 4 Eliminating Oxygen from the Purge Gas and the use of Monitoring Equipment

Even using specialised weld purging equipment does not guarantee defect free welds. Control of the oxygen content of the purge gas is crucial to success.

In this final part of the series the significance of maintaining a low level of oxygen in the purge gas is considered. Several factors will determine what oxygen content can be tolerated in order to prevent oxidation, the most crucial being the material being welded. Sensitive alloys such as titanium may require oxygen to be limited to 50 ppm1 whilst some stainless steels will tolerate 150 ppm without noticeable surface discolouration.

The first, and crucial, step and an aspect often overlooked is the need to provide effective sealing around the weld zone. Poor sealing invariably allows air to enter the weld zone and thus defeat the objective of providing a low oxygen environment.

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WP-269 Shielding Gas and Purging Techniques during Welding-Part 3

HFT Weld Arc Orange PHO 08D

Part 3 Welding Enclosures and Trailing Shields

In Parts 1 and 2 the author outlined the problems in selecting the optimum gas for use during weld purging and then analysed the options available to engineers when choosing a purging technique for tube and pipe welding.

This article examines protective enclosures and trailing shields as potential solutions to the need to prevent contamination during welding.

Welding Enclosures

Traditionally, permanent metal enclosures have been used when welding materials that are sensitive to contamination from atmospheric gases. Such enclosures may be evacuated using vacuum pumps or purged with inert gas.

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WP-269 Shielding Gas and Purging Techniques during Welding-Part 2

HFT PHO 02A Industrial Pipelines 123rf

Part 2 Pipe and Tube Weld Purging

In Part 1 Dr Fletcher set out to show many inconsistencies in the approach to weld purging, especially in the choice of gases used.

His conclusions were as follows:

Much more definitive work is now essential if fabricators are able to proceed with confidence in consistently producing welded joints capable of meeting the demanding standards imposed by service conditions. In the meantime the precautionary note from the American Welding Society offers the best advice with a conclusion that the shielding gas needs to be matched to the metal composition.


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WP-269 Shielding Gas and Purging Techniques during Welding- Part 1

HFT Welding Tube Orange PHO 15B

Part 1 The Importance of Gas Control on Weld Quality

Some form of gas protection is necessary during welding of many metals, but in particular stainless steels and titanium alloys, to maintain their physical properties and to prevent reduction in corrosion resistance. Which is the best gas and which is the best technique to use when weld purging are principle questions facing engineers.

Dr Fletcher sets out in this 4 part series, to cover all related topics including gas selection and purging equipment. He has researched published material on the subject of protective gases from a very wide range of sources. Typically this has included steel manufacturer, major users (ref.2), consumables and equipment suppliers (ref.3) independent authorities (ref.4) and many welding engineers (ref.5,6,7).

Argon, as a totally inert gas, is the most commonly used, but nitrogen and hydrogen also offer protection. Helium offers the same protection as argon but is seldom used because of the cost.

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WP-271 Titanium in Motor Sport

31W FlexibleWeldingEnclosuresRacing car recreated using advanced welding technology

With the progressive development of racing cars has come a need to embrace fusion welding as an essential part of the manufacturing process.

Whilst dramatic improvements in engine design have made a significant contribution to track performance, reduction in weight and aerodynamic refinements have also been important. Safety conventions need to be continuously revised to protect drivers in the event of accidents.

Welding has played an increasingly important role during production of body parts. Reduction in weight has been achieved by using slender suspension and steering components and replacing steel with lower density titanium.

Fabrication of titanium alloys however requires skills orders of magnitude greater than steel: they are difficult to form and challenging to weld.

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WP-207 Single Ended Purge Dams

03W-InflatableWeldPurgeDamsUpdate 2017 - revision 3


It took a long time for engineers to recognise that the use of inert gas purging during the welding of tubes and pipes could not only improve overall weld quality but could save both time and money.

Purging using designs based on advanced technology offers dramatic reductions in weld defects, significant savings on welding time and elimination of post weld cleaning operations. All this simply by effectively protecting the rear and the topside weld beads from contamination, and especially oxidation, using inert gas coverage. 

Purge systems have evolved rapidly during the last decade as advances in materials and control equipment have been incorporated.

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WP-205 Help with Nickel Alloy Welding

HFT-PHO-02A-Industrial-Pipelines-123rfAlloys based on nickel are used widely in industry sectors such as petrochemical, aerospace and power generation where resistance to chemicals and mechanical strength at high temperatures is required. The Nimonic and Monel alloys are the most common proprietary metals, but the total range is extensive, covering nickel contents from 30% to 99%.

Applied with care, all the conventional welding processes can be used to weld nickel and its alloys1,2 and the basic technical aspects have been understood for many years. It is however essential to ensure that contamination does not occur—the nickel alloys are particularly susceptible to cracking and porosity if the welding environment is not properly controlled.

Machining or vigorous stainless steel wire brushing followed by thorough degreasing with a suitable solvent is necessary prior to welding, with the welding taking place within about eight hours to reduce the risk of contamination.

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WP-201 Advances in Weld Purge Gas Oxygen Monitoring Technology

52W-PurgEye100-IP65-WeldPurgeMonitorThe importance of gas purging when welding stainless steels has long been recognised, particularly in the more sensitive sectors such as petrochemical, pharmaceutical, cryogenics, food and drink and semiconductor. The presence of oxygen causes, at best, an unsightly appearance but, more significantly, oxide deposits on the joints can become detached and lead to serious product contamination 1,2 3,4.

Recent research undertaken by technologists at Huntingdon Fusion Techniques, HFT® has revealed some startling evidence. Whilst existing Weld Purge Monitors® can be applied confidently to take measurements close to the welding source i.e. within one metre, they have been shown to have shortcomings beyond this distance.

Recognising the need for more precise remote monitoring, HFT® has developed a unique purge gas measuring instrument with which accurate and rapid observations can be made up to one kilometre from the weld. For quality control purposes the instruments can be integrated into a recording and data processing system.

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WP-197 Additive Layer Manufacturing (ALM)

Welding makes major impact on 3D printing technology.

Additive Manufacturing WAAM 3D PrtintingSince 3D printing was introduced there have been a number of developments, but the more recent use of fusion welding as a deposition source has opened up wide ranging possibilities in manufacturing.

The process is one in which metal is deposited layer-by-layer to form a three dimensional shape (Fig 1). Various melting techniques have been used to achieve this aim including electron beams and lasers but one being actively pursued currently is Wire and Arc Additive Manufacture (WAAM) using a GTAW (TIG) power source. 

Fig 1.
Titanium alloy airframe wing spar created using robot control of GTAW.


Driving Forces Behind the Development of WAAM

The primary driving force behind the development is the potential to make huge savings in materials and therefore costs.


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WP-73 Advanced Freezing Technology Finds Applications in Maintenance

Characteristics of Measuring Weld Purge Results from a Distance.

34W Accu Freeze Pipe Freezing SystemsPipework users across the entire industrial spectrum occasionally face the problem of having to repair or replace pipe sections or change in-line components such as valves and instrumentation.

The conventional approach to these problems involves isolating and emptying the appropriate section. This might necessitate draining a large volume of product and could also cause serious interruption to production.

An attractive and economical solution is to freeze the pipe contents upstream of the repair or component replacement zone.

Alternatively, freeze both sides of the repair site and simply drain the material between the freezes.  

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