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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WP-63 Remote Weld Purge Monitoring

Characteristics of Measuring Weld Purge Results from a Distance.

03W-PurgEye500-WeldPurgeMonitorCircumstances occasionally arise, particularly during on-site welding of pipelines, when it becomes necessary to measure purge gas oxygen content using instrumentation located some distance from the joint.

The accepted method of monitoring is to extract gas down a tube and take measurements at the exit of this exhaust tube.

Whilst this technique yields good results when the tube length is short, if below one metre, readings become inconsistent and unreliable once the sampling distance exceeds this.

In order to establish the reasons for this variation in readings Huntingdon Fusion Techniques, HFT® has initiated laboratory research but based on commercially available equipment.


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WP-59 Flexible Welding Enclosures®

Flexible Welding Enclosures® and Their Comparisons with Metal Chambers and Glove Boxes.

04W-FlexibleWeldingEnclosuresMany of the metallic materials in common use now are prone to contamination when in contact with atmospheric gases, such as oxygen, nitrogen and hydrogen.

This is particularly the case when this contact occurs at the high temperatures prevailing in fusion welding.

Control of contamination can be effected in the majority of cases by shielding the local welding area with a protective inert gas such as argon, as in GTAW ( TIG welding ) or by introducing a protective slag as in MMAW ( stick electrode welding ). 

With many metallic materials however, including some titanium and nickel alloys, more stringent precautions are necessary and to ensure satisfactory weld quality the entire joining process needs to be undertaken inside a vessel from which all potential contaminating products have been removed.


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WP-52 Gas Purging Optimises Root Welds

Results in Quality Pipe Welds

04W-PurgEliteWeldPurgeSystemsIn circumstances where welds have to be designed to withstand stress in service, special consideration needs to be given to their metallurgy and profiles.

The mechanical properties of welds, particularly their fatigue properties, can be influenced significantly by their shape and composition. In particular, at the weld root, a positive reinforcement combined with smooth transition from weld to base metal is a pre-requisite to achieve optimum mechanical strength.

Good Practice

Joints of high quality between cylindrical sections such as tubes and pipes can only be made by ensuring that atmospheric gases are eliminated, and positive, smooth weld reinforcement is provided.

The presence of oxygen, and to a lesser extent nitrogen around the molten weld can lead to wide ranging defects. Discoloration is unsightly and in some instances might reflect metallurgical imbalance, especially with some stainless steels.

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WP-51 Freezer Solutions to Pipe Repairs and Alterations

Freezing your Pipes

02C Qwik FreezePipework 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.

 Isolating and Exposing Sections for Attention can be Very Expensive

  • Pipelines need to be emptied of contents be they solid, liquid or gaseous
  • The contents need to be disposed of or stored
  • Systems need to be re-filled following any work
  • Production needs to be interrupted

An attractive and economical solution is to freeze the pipe either side of the repair or replacement zone. Only the volume between freezing points requires emptying. Two solutions are available, the first covering pipe diameters from 9 – 200 mm (3/8" – 8") and the second up to 300 mm (12").

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