Welding processes can weaken metals by imparting residual stresses into a material, leading to a reduction in corrosion resistance properties. Post Weld Heat Treatment (PWHT) is regularly used to retain the strength of a metal when welding certain materials including high strength stainless steel and chromium-molybdenum (chromoly) steel such as P91.
Temperatures during PWHT might reach as high as 760ºC (1,400ºF) for many hours, during which time the insides of the pipes need continuous purging using Pipe Weld Purging Products. Many purging materials cannot withstand these temperatures, nor resist damage during the time at temperature.
HotPurge® Pipe Purging Systems have been designed and developed by Huntingdon Fusion Techniques HFT® for Heat-Treated Chrome and High Strength Stainless Steel Pipe Joints.
Weld Purging is essential when welding tubes and pipes made of reactive metals such as stainless steels, titanium and zirconium.
Usually weld zones are confined with purge dams so that the use of argon purge gas is limited and waiting times are reduced. Homemade dams fabricated from paper, sponge foam, wood etc. all contain water as a liquid or a vapour. Water vapour will outgas into the purge volume during the weld process, forming oxides with the metal being welded and create the imperfections that the dams were intended to stop.
Oxidised welds will lead to rework of some kind and in bad cases cause welds to be rejected and having to be cut out and re-welded. Displacing the oxygen with an inert gas before, during and after welding helps to create welds that are free from oxidation, however the weld purge dams should be made of materials that do not outgas water vapour or any other undesirable gases.
For pipe and tube lines, the most cost-effective solution is to restrict the volume around the joint with an inflatable Tandem Weld Purging System that is available off the shelf and designed especially for the task.
Welders are often faced with challenges where high quality stainless steel, duplex and chrome steel welds are required, but where the use of purge gas is not always possible.
One solution to this problem is the use of Argweld® Weld Backing Tape™ from Huntingdon Fusion Techniques HFT®. This high temperature resistant glass fibre tape supports weld roots and eliminates the creation of slag, while removing contact with air to dramatically reduce the amount of oxidation.
Luke Keane, Technical Sales Manager for HFT® said: “Weld Backing Tape™ is a common material used for manual and automatic welding to achieve higher welding speeds and dramatically reduce the amount of post weld cleaning.
The HFT® glass fibre Weld Backing Tape™ has no true melting point so it works satisfactorily with TIG or MIG welding (GTAW or GMAW) where temperatures can reach up to 6,000ºC. This overcomes the concerns associated with ceramic fibre versions that have a melting point of 1,800ºC,
Sealing, stopping and blocking pipes where oils, hydrocarbons and petrochemicals are present can cause major inconveniences with many normal stoppers not being able to handle such conditions.
The Pipestoppers® Division at Huntingdon Fusion Techniques HFT® manufactures a Range of Inflatable Rubber Plugs for heavy-duty applications where pipes might contain liquids and gases that usual Inflatable Stoppers are not resistant to.
HFT®’s Lightweight Inflatable Rubber Plugs can withstand temperatures from -40°C (-40°F) to 70°C (158°F) and are available in sizes from 2 to 78” (51 to 1,981 mm) with each Plug having a wide degree of flexibility in diameter.
Ron Sewell, Chairman for HFT® said: “Inflatable Rubber Plugs are highly resistant to oils, hydrocarbons and petrochemicals. They are used during new pipeline installation or for carrying out routine maintenance and repairs.”
Often when welding lengths of tubes and pipework fabrications of 20 metres or more, measuring the purge gas might not always easy. Under these conditions, there is a risk of contamination of the gas exiting the weld zone, leaving the welders uncertain about their welds and welding procedure.
Weld Purging Experts Huntingdon Fusion Techniques HFT® have designed and developed the PurgEye® 1000, a localised sensor with long distance cable that displays the oxygen level in the welding zone on a Weld Purge Monitor® screen that might be 10, 50 or even 1,000 metres away from the weld.
The PurgEye® 1000 comprises a stainless steel housing with a sensing head that can be fitted onto any Pipe Weld Purging System or simply left in the welding zone and have the oxygen levels transmitted electronically to a monitor up to 1 km away.
Repairs or modifications on pipes can pose challenges, especially where there is liquid present inside, which may result in the expense and danger of system down time and loss of revenue while the system is drained and refilled.
To dramatically reduce these costs and speed up the repair or replacement enormously, Qwik-Freezer™ is available from the Pipestoppers® Division of Huntingdon Fusion Techniques HFT®.
Ron Sewell, Chairman for HFT® said: “Qwik-Freezer™ is quick and easy to use, requires little set-up time and is the only CO2 Pipe Freezing System capable of freezing up to 8” pipe. Even for smaller diameter freezes, Qwik-Freezer™ produces ice plugs that are significantly more reliable and robust, capable of withstanding far more pressure than the smaller freeze plugs that other types of systems will produce.”
Metals that are classed as ‘reactive’ (titanium, zirconium and nickel alloys) are sensitive to oxygen when heated. When welding these metals, the oxygen must be purged from the welding zone, down to as low as 10 parts per million (ppm). Weld Purging in this environment will avoid discolouration of the weld and heat affected zone and limit oxidation that could lead to a loss of metals’ corrosion resistant properties.
Welding in an atmosphere of 40 ppm or less will help to guarantee the greatest weld joint strengths and the highest resistance to corrosion. Therefore monitoring the oxygen content before, during and after welding is crucial.
With restricted budgets in mind, Huntingdon Fusion Techniques HFT® have designed and developed the low cost entry level PurgEye® Nano Weld Purge Monitor®.
Large diameter pipework can cause several challenges, especially when those pipes are manufactured from stainless, duplex and chrome steels, titanium or zirconium. When welding such reactive materials, they need to be purged of oxygen before, during and after welding.
It is not cost effective to completely fill pipework with expensive inert gas, so weld purging experts Huntingdon Fusion Techniques developed QuickPurge® Systems to dramatically reduce the space that needs to be purged.
Ron Sewell, Chairman for HFT® said: “Using QuickPurge® means there is no longer a need to fill complete pipework fabrications with an inert gas. These devices localise the gas purging to a space about 10” (250 mm) either side of the weld to reduce purging time dramatically, making huge savings in both purging time and gas costs.”
Eliminating oxidation and discolouration when welding stainless and duplex steels as well as titanium, zirconium and nickel alloys is crucial in many industries today, because of improving quality control procedures. Welds have to be free from metallurgical defects otherwise they can potentially be rejected, often leading to a significant loss in time and resources.
The quality of welds on tubes, pipes and flat sheet metal can be dramatically improved with the addition of a low cost Weld Trailing Shield®.
Huntingdon Fusion Techniques HFT® have designed and developed Argweld® flat and radiused Trailing Shields® which simply attach onto any TIG/GTAW, PAW/Plasma and MIG/GMAW welding torch, providing an additional inert gas coverage during welding of reactive metals where discolouration or oxidation needs to be eliminated.
The Tungsten Electrode is one of the most important variables involved in TIG welding. Preparing your Tungsten Electrode correctly will help to improve arc starting, arc stability and weld quality.
Tungsten Electrode Grinders are a convenient, safer and more accurate way than other methods of grinding Tungsten Electrodes. Huntingdon Fusion Techniques HFT® now manufacture the TEG-1000 Tungsten Electrode Grinder with a diamond wheel, producing smooth, perfect surface finishes that eliminate arc jumping leading to consistent welds.
Ron Sewell, Chairman for HFT® said: “An incorrectly ground Tungsten Electrode tip may drop into the weld pool and create a tungsten inclusion that could lead to a weld cut-out or reject, either way, leading to additional welding costs and lost time. It can also result in a huge reduction in tip life and changes in arc voltage.”
New power plants are in high demand and several hundred are expected to be built over the next decade. Chromium-molybdenum (chromoly) steel pipe such as P91 is a major construction material for the high pressure piping in these plants and there are particular techniques for welding this pipework to avoid potential catastrophe caused by oxidation.
Pre-heat and post-weld heat-treatment are mandatory and absolutely critical to the service life of the alloy. Chromoly is a low alloy steel and has also been used to produce tubing for bicycle frames and racecar roll cages. It is not as lightweight as aluminium alloys, but has the advantages of high tensile strength and malleability.
To ensure the welds are free from oxidation, which could otherwise lead to a loss of corrosion resistance, they must be welded with an excellent shield of inert gas, both inside and outside the pipe joint.
Weld Purging smaller tubes and pipes of different diameters can be challenging, especially when budgets are tight. Often, Welders are left to create their own homemade purging dams out of unsuitable materials such as foam, paper or cardboard.
Huntingdon Fusion Techniques HFT® have designed and developed clinically clean, white Nylon Weld Purge Plugs™, providing a great barrier for weld purging at a very low cost.
Luke Keane, Technical Sales Manager for HFT® said: “For welding complicated nickel alloy, titanium and stainless steel tubes and pipe joints as well as stubs, elbows and tees, Weld Purge Plugs™ are a perfect product to seal all holes and orifices for quality internal weld purging. They can also be used for weld purging small or odd diameter pipes where conventional inline pipe purging systems may not be practical.”