[huntingdon_fusion]

High quality welds in pipes and tubes can only be assured if the weld underbead is protected from oxidation. The various techniques available through which protection can be given is referred to as purging.

The Pre-Purge Process

A pre-purge is used to displace air present in the pipework system or dam volume. Numerous factors control the pre-purge time such as pipe diameter, purge volume and maximum permitted oxygen level. A common misconception is that increasing the purge flow rate will reduce the purge time. This is falacious. Increase in flow rate increases turbulence and results in unwanted mixing of purge gas and air and can actually extend the purge time. As a general rule the pre-purge flow rate and time should allow for about five volume changes in the pipe system or dam volume but a typical gas flow rate will be in the region of 20 l/min.

Weld joints that require a root gap or which exhibit bad end matching, both of which characteristics provide an unwanted leak path for the purge gas, can be sealed by taping.

Oxygen and moisture levels in the purge gas should be checked using appropriate equipment. Whilst 0.1% residual oxygen is a suitable working level for materials such as some stainless steels, the level needs to be lower than 0.01% when welding the more sensitive alloys based on titanium and other reactive metals. Recent research indicates that levels for welds in the pharmaceutical, dairy and semiconductor industries need to be below 0.001%.

The Weld Purge Process

Once the quality of the gas in the dammed volume has reached the required level, gas flow can be reduced to about 5 l/min for the welding operation. On a more practical level it should just be possible to feel the gas flow from the exit point. Excessive flow can cause the internal pressure in the pipe to rise and create concavity in the weld root geometry and in more extreme cases can cause complete ejection of the molten weld pool.

On joints which are not fully sealed to restrict leakage a higher flow rate will be necessary to avoid contamination. Towards the end of the weld run however, as the joint becomes permanently sealed, the gas flow rate will need to be reduced to avoid over-pressurisation.

Weld Purge Techniques

There are six principle methods available for pipe purging.

Screwed up paper
Open Pipe Operation
Soluble Discs
Expandable Plugs
Flexible Discs
Inflatable Systems

Generally the simple and low-cost solutions may well serve to offer limited protection but they are far from being totally reliable.

It's hard to believe that the use of screwed-up newspaper, plastic foam or cardboard discs to block the pipe on each side of the joint and rely on this as an effective seal is still considered by some to be adequate. Even if they don't burst into flames during the welding cycle the problem of removal after completion of the joint is rarely considered.

For small diameter tubes, say up to 10 mm, the use of continuous inert gas flow without seals is not uncommon. Air is replaced by incoming inert gas. However it overlooks the possibility of turbulence and thus entrapment of oxygen. Continuous gas flow can also be costly.

Expandable pipe plugs can be very effective and cheap. These are widely used for pipe pressure testing and volume production means that cost is low.

The sealing area is large and the time involved in preparation is relatively small. Plugs are available covering diameters up to 1000 mm and whilst the smaller plugs are available with nylon bodies, aluminium and steel are used above 150mm. The larger and therefore heavier versions may thus be difficult to insert and remove if the joint line is more than 500 mm from the access point.

Soluble barriers cut to pipe size and glued to the internal diameter provide some degree of protection and the discs can be removed by flushing with water after use. The bond to the pipe is prone to leakage however and the time and skill involved in preparation can be considerable.

These are suitable for low volume weld production where time is not of the essence and access to joints is readily available. Paper and engineering plastic versions are available but paper versions may not be suitable for site work because of their fragility. Time, dexterity and patience are required during application and the film can only be inserted as far away from the pipe access as an engineer can reach.

Flexible ‘floppy’ discs connected by a flexible tube are available. They can be deployed quickly and removal after welding is easy since the assembly can be withdrawn past the weld. Reliability is suspect however because disc to pipe sealing depends upon a very small contact area. Some have a semi-rigid connecting tube and this may be unsuitable where the system needs to be used either side of a sharp pipe bend.

http://huntingdonfusion.com/index.php/e ... -and-pipes

[Coldman]

I gotta buy it. Where do I send the money?

[Braehill]

A link in your signature line would have been a better approach. This isn't an ad board, it's a community of welders and fabricators sharing ideas and offering each other help. If you want to promote products without offering any other input to the group please take it somewhere else.

If in fact you have something other than your own commercial interest in mind that you can contribute, feel free to use the introduction thread and tell us a little about yourself. You'll find us very cordial when we don't feel like we're dealing with a snake oil salesman.

Len

[LtBadd]

A link in your signature line would have been a better approach. This isn't an ad board, it's a community of welders and fabricators sharing ideas and offering each other help. If you want to promote products without offering any other input to the group please take it somewhere else.

If in fact you have something other than your own commercial interest in mind that you can contribute, feel free to use the introduction thread and tell us a little about yourself. You'll find us very cordial when we don't feel like we're dealing with a snake oil salesman.

Len

Just about anytime I see an article in a trade publication on purging its always Huntingdon and their products, haven't ever used them so can't make any comments on the quality of the product

[Superiorwelding]

huntingdon_fusion,
Welcome to the forum. I appreciate the informative copy and paste article and I know you can add to purging conversations but as was already mentioned we do not allow members here to solely promote their products. I encourage you to participate in discussions in your area of expertise and you can suggest a product or two along the line, especially if it is the correct solution to a given problem, but outright advertising is not allowed. We respectfully ask you honor the moderators wishes and the forum rules.
-Jonathan

[huntingdon_fusion]

huntingdon_fusion,
Welcome to the forum. I appreciate the informative copy and paste article and I know you can add to purging conversations but as was already mentioned we do not allow members here to solely promote their products. I encourage you to participate in discussions in your area of expertise and you can suggest a product or two along the line, especially if it is the correct solution to a given problem, but outright advertising is not allowed. We respectfully ask you honor the moderators wishes and the forum rules.
-Jonathan

A link in your signature line would have been a better approach. This isn't an ad board, it's a community of welders and fabricators sharing ideas and offering each other help. If you want to promote products without offering any other input to the group please take it somewhere else.

If in fact you have something other than your own commercial interest in mind that you can contribute, feel free to use the introduction thread and tell us a little about yourself. You'll find us very cordial when we don't feel like we're dealing with a snake oil salesman.

Len

Hi Jonathan and Len, thank you for the information. I have edited my post to ensure there is none of our product information on there. Ideally I would like to stimulate a discussion about purging as it is not readily discussed on these forums, to include methods of use, most effective ways to purge etc.

Best wishes
HFT

[Superiorwelding]

HFT,
Thank you for that. I look forward to the discussion as I get into purging different items and want to get into the purge chamber market as well.
-Jonathan

[Oscar]

Purging not discussed in a tig welding forum? When isn't it discussed

[Braehill]

HFT,
We do on occasion get into discussions about different methods of back purging, especially in our Tig welding threads. Your contributions to the discussion are as welcome as any other member here and we look forward to hearing from people with real life knowledge on any subject. What we don't like, as was stated, to be sold to.

We're a little more personal than most forums so if you can contribute in the future please include your first name, it seems friendlier. We didn't get off the our best foot.

Len

[huntingdon_fusion]

We are in the process of creating Heat Tint Recognition Charts For Titanium and Stainless Steel Welding.

They will be available soon with 18 images of colouration reference.

Would any of you be interested in pre-ordering a free copy?

[Rick_H]

We are in the process of creating Heat Tint Recognition Charts For Titanium and Stainless Steel Welding.

They will be available soon with 18 images of colouration reference.

Would any of you be interested in pre-ordering a free copy?

Sure....

[big gear head]

Could you explain to me what this chart is for and how to use it? I haven't heard of this before. I would probably be interested if it was useful to me.

[weldin mike 27]

A picture of a stainless weld, with the colours on it, and an explanation of what the different colours mean. IE rainbow = 400° blue 300° grey/black 600• or something like that

[LtBadd]

We are in the process of creating Heat Tint Recognition Charts For Titanium and Stainless Steel Welding.

They will be available soon with 18 images of colouration reference.

Would any of you be interested in pre-ordering a free copy?

Ron I am also interested, PM sent

[big gear head]

How is this useful? Is there an application for it?

[LtBadd]

How is this useful? Is there an application for it?

Well without seeing the chart and what it reveals, I'll say that getting good gas coverage is always a concern to obtaining the best weld. the more you know the better you can apply the knowledge in your trade, and I'm all for knowing more. Bottom line is let's see if we can learn something here...

[zank]

How is this useful? Is there an application for it?

It helps with QC. The charts provide example pictures of what is acceptable and rejectable for titanium and stainless. The different colors you see represent different amounts of contamination in the weld and HAZ. You can compare the weld with the welds in the pictures and determine if the piece is acceptable or not.

[dirtmidget33]

It is prolly similar to this Miller one. Miller one might not be as detailed as one he is offering. Sure his is a card format to carry in field for inspectors or welders. Obviously silver is great this chart let's you know what might be acceptable or be able to get by with and what needs to be junked.

Titanium-poster.jpg (40.42 KiB) Viewed 1333 times

Link where this is at on Miller site
http://www.millerwelds.com/resources/ar ... um-welding

[Rick_H]

AWS D18 is for sanitary applications, I think it's d18.2 has a heat tint chart for inside of tubing as far as acceptance. If the purge and fit up is correct, basically no color is present.

Even using a jumbo cup I still have color welding 316L tubing for sanitary apps, but once pickled and polished they are mirror like and near non existent. I don't stress as much on the outside color anymore as long as I know I'm not overheating. Very hard to get a strw color all the way around a 1.5" tube, 100% penetration

[big gear head]

OK, I weld a lot of 304 and 316, and some titanium, so sign me up for one.

[LtBadd]

AWS D18 is for sanitary applications, I think it's d18.2 has a heat tint chart for inside of tubing as far as acceptance. If the purge and fit up is correct, basically no color is present.

Even using a jumbo cup I still have color welding 316L tubing for sanitary apps, but once pickled and polished they are mirror like and near non existent. I don't stress as much on the outside color anymore as long as I know I'm not overheating. Very hard to get a strw color all the way around a 1.5" tube, 100% penetration

Rick, nice looking welds, do you use a rotator?

[Rick_H]

Thank you very much

Nope all by hand in just about any postion and I've learned to be quite the contortionist....lol

[huntingdon_fusion]

The Heat Tint Recognition Chart show different images of weld discolouration in order to gage the acceptability of colour in the heat affected zone. The Charts apply to titanium and stainless steel.

Anyone who would like a copy of the Charts, please inbox me with your name, company and postal address.

Thanks