The causes and solutions for the generation of transverse cracks in welds

What causes transverse cracking? How can it be solved? I believe I have some methods to minimise transverse cracking. And it is a very inexpensive method. Please see my analysis and explanation below.

What causes "transverse cracking"? Many people have investigated and researched, but have not been able to find out the real cause and a complete solution.

Based on the results of my research over the years in China and abroad, I have found that transverse cracking is mainly caused by two welding methods, submerged arc welding (SAW) and gas shielded flux cored welding (CO2+FCAW), especially CO2 gas shielded flux cored welding.

I believe that the causes are not single factors, but at least two or more causes of safety accidents, such as someone jumping from a height because the ground is sloping unevenly, and as a result, they break their back. If the ground is flat it's fine to jump, and conversely the person doesn't jump down even if there is a knife on the ground it's fine! This means that it took at least two factors to cause a safety accident.

I think it is most appropriate to use the word cancer as a metaphor for transverse cracks. When our ancestors created the word cancer, they told us that the word for cancer is a disease in itself, and that it is the result of three mouthfuls of toxins piling up to form cancer.

Transverse cracks are rare in our regular welding, for example: porosity, slag, unfused, biting edges, etc. are common, as if we often have a bit of cold and flu and diarrhoea; occasionally there are longitudinal cracks and cold cracks on the edge of the weld toe, also like we accidentally break hands and feet in sports, which is also easy to understand and prevent, while cancer is rare, but when you see it it is already It is too late to see it, it is a death sentence and it is almost hopeless. Transverse cracks are also like cancer cells that spread and metastasise, and the more you repair them the more they crack, following the air bubbles and blossoming all over the place.


We also have three ports when welding this is.


1. base material;
2. welding material;
3. welding process.

Base material

High strength steel with high carbon content is more prone to transverse cracking than low carbon steel, TMCP material due to its unique production process, resulting in it being a more sensitive material, the base material contains other non-metallic impurities, large thickness, with sandwich, surface corrosion and rust, etc.

Welding materials

Submerged arc welding and flux cored welding both have in common that there is a flux powder (flux), they are in the process of manufacturing, a variety of ingredients used in the purity of the lack of impurities or itself with impurities, will affect the performance of the weld. Welding consumables industry competition is fierce, in order to maintain profits to switch to other cheap formulas or use the purity of materials (cutting corners), which will reduce the welding performance or called crack resistance. If some welding consumables factory does not pay attention to each production link, in the process of production and inventory on the moisture, wait until the user is too late to use.

Submerged arc welding in the welding process to recover no melting flux powder, will be absorbed back into the hopper together with other impurities, especially in the continuous production of spiral welded seam, in the mechanical strength of the pipe roll at the same time a large number of steel plate surface oxide (oxide skin) off with other sand and dust powder slag and other mixed in the medicament and then re-enter the weld pool, resulting in pollution, and then meet the medicament moisture, the base material preheating and insulation is insufficient When the time, will also produce transverse cracks.

The quality of flux cored wire varies from brand to brand, and improper storage and use of the wire is also a source of transverse cracking in the weld. The first is that the wire is manufactured in two types of packaging - plain and vacuum packed. If the wire is stored in a controlled environment indoors in plain packaging and used up within a short time as required by the manufacturer, it is fine. If the wire is improperly stored in plain packaging, inadequately protected in transit, or improperly handled by an intermediate distributor, the wire becomes damp and is used in a natural environment without any protective measures, allowing the wire to become further damp and otherwise contaminated, which can also cause transverse cracks.

Whether in plain packaging or vacuum packaging, manufacturers require users to use the wire within 24 hours of opening, and to store it in a dry box when not in use during a break. If welding outdoors where there is rain, snow, dew or sea breeze, the wire must be covered with a protective cover with waterproofing properties to be used, and must not be used again more than 24 hours after opening, whether with or without a protective cover or in a dry box. This is something that no one seems to know in China. We do not use protective covers indoors or outdoors, we let the wind and the rain blow, we have no concept of time and no concept of difference between indoors and outdoors. In fact, even indoors, in spring and winter, in cold and damp climates, it is very humid indoors and we are able to use a 15kg roll of welding wire for more than 24 hours, 48 hours or even "year round".

Please see below the "StorageConditionsandUsagewire" from a foreign brand of wire manufacturer to the user:

StorageConditionsandUsagewithFCWS Flux Cored Wire Storage and Use Precautions

1. Packingofwires

Eachwirespoolshallbecoveredwithapolyethylenefilmandfurtherpackagedinthecorrugatedboxforprotectionduringtransportationorstorage.


2.Recommendedablestorageconditionfornon-openedwiresincorrugatedboxes


2.1Wiresshouldbestoredinawarehousefreeofrain,snow,ordewetc.


2.2Theyshouldnotbeputonfloordirectlybutonawoodenpallet.

2.3Itisdesirablethattheyarestoredinaplaceoflesshumidity

3Countermeasuresaboutopen-packedwires

3.1Itisnotnecessarytoredrythem.Ifredrying,theplasticspoolmightbetransformedbyheat.

3.2Whenweldedattheplacesufferedfromrain,snow,dewandseabreezeetc.,thewirefeedershouldbeprotectedbywaterproofcover.

3.3Itisdesirablethattheyareusedinaplaceoflesshumidity.

3.4Spool-openedwiresshouldbeusedwithin24hours,iftheyareleftafterworking,theyshouldbestoredunderdryconditions.

Inthiscase,thesurfaceofeachwireshouldbecoveredwithapolyethylenefilmorsheetforprotection.

The welding process is one of the most important causes. The welding process is a set of process procedures and their technical provisions including: welding methods, preparation processing before welding, assembly, welding materials, welding equipment, welding sequence, welding operations, welding process parameters and post-welding treatment.

3.1 In the welding process from the bevel prefabricated, grinding, grouping, bevel angle clearance, surface treatment, workpiece preheating, insulation, slow cooling after welding to remove hydrogen and so on;

3.2 Whether the welding process is operated strictly according to the welding process already done;

3.3 Whether the welder holds the appropriate qualification;

3.4 Whether the welding environment is windproof, rainproof, snowproof, dew-proof, moisture-proof, and light-permeable lighting appropriate safe and reliable;

3.5 Whether the surface of the weld is clear of oil, water and rust;

3.6 Whether excessive use of carbon arc gas planer, open bevels, root cleaning, multiple reworking without removing its carbide and welding, gas planer compressed air is removed from the water? ;

3.7 improper maintenance of the welding machine and welding gun, can not play the proper welding performance;

3.8 welding process on the wire does not take due protection and use more than the time limit or the use of moisture contaminated wire;

3.9 submerged arc welding agent using different brands of welding wire, the agent is not fully dried, the agent in the recovery process will be steel oxide (oxide skin), other impurities, welding slag, sand and dust powder, etc. together with the absorption, again into the welding caused;


3.10 The internal stress of the workpiece combination is too large, there is no control over the welding deformation, the resulting constraint stress is too large beyond the tensile stress that the weld can withstand;


3.11 NDT inspection is too high requirements and me reworking back to cause more defects;


3.12 A weld with a large number of passes is also a cause of transverse cracking due to the accumulation of impurities in the weld;



3.13 The shape and order of the weld arrangement will also affect the constraint force (internal stress) within the weld; of course, there are other improper things in the welding process I will not name them here.


Summary

Although the causes of transverse cracking are many, but I personally think the main reason in the flux cored wire, the parent material aspects of the problem is less, because we use the marine steel structure are ordinary low carbon low alloy steel, welding process is also mature and commonly used, our main focus on the flux cored wire monitoring aspects.


I have 10 'Code of Practice' suggestions for the use of welding wire

1. Vacuum pack whenever possible;

2. Use small 5kg packs (or at height, in open spaces, in cramped conditions, etc.);

3. Cover the wire with a waterproof cover when welding in open areas;

4. Store in a dry box during breaks or when not welding for more than 1 hour;


5. Do not use the product for more than 24 hours after opening;

6. Do not use if rust or discolouration is seen when unpacking;

7. Do not use the wire when it is wet with rain or other pollution;

8. Stop using the same batch of wire when there are transverse cracks until the cause is found.

9. If possible, we can monitor the production, stock and transport of the wire in the same way as we inspect the steel material in the steel plant.

10. Take a return claim and no longer use the penalty system to choose a good quality and reputation of the welding material factory.

In the 80's and 90's there was no domestic ability to produce flux cored wire, I used to design CO2 gas shielded flux cored welding lines for two Japanese companies in Hong Kong, using all foreign flux cored wire. 24 hours of continuous work, for years and years and in the open field, I just used oil drums to cover the weld seam for welding, thousands of components whether spring, summer, autumn and winter never saw transverse cracks.

Now that foreign brands have entered domestic production and some domestic manufacturers are able to produce flux cored wire, the question arises. I recently visited one of the most famous international welding wire factories in China and they did this by acquiring a Taiwanese owned welding wire factory that had set up a factory in China and then hung the foreign brand with Taiwanese machinery and domestic people to manage and produce it. The production equipment is not advanced, coupled with a similar attitude to work in everything, so I saw that in early spring in March in the south of the Yangtze River, the sky was cloudy and raining, hazy and misty and very humid, the first warm weather was particularly chilly and cold, even I felt chilly in my down coat. The workshop door was open and the production was carried out in an uncontrolled temperature and humidity environment, which in itself made it possible for the wire to be damp.

Many people think that flux cored wire is sealed, but it is not, it is made of thin steel plate involved in the flux powder, no matter how tightly it is rolled into a tube, it will also inhale moisture, just like we do penetration detection principle of capillary infiltration, the centre of dry flux powder is very easy to inhale the moisture. What's even more annoying is that it can't be dried again with high temperatures like a manual electrode.


Many years ago I once saw a notice on the door panel of the construction workshop to punish the welder, it was about a welder who did not connect the power cord of the insulation cylinder in time because it was loose, so that the QC personnel found the result to be fined RMB 100 yuan, think about our migrant workers years ago how many 100 yuan can be paid? How harsh is this!

Why is it so harsh? Because we all know that low hydrogen welding rods can cause delayed cracking if they get wet, a consensus that has long been formed in the days when welding rods were used. But now many of us do not know that flux-cored wire is more demanding than electrodes, especially some welding masters blindly believe that flux-cored is the universal wire, only to see its efficiency without seeing its most dangerous side. I believe that flux cored wire should be more strictly managed than electrodes, and now all of us involved in the construction should know that flux cored wire should be protected from moisture like electrodes, forming a consensus to jointly regulate flux cored wire. By applying the electrode management approach to flux-cored wire, I believe that transverse cracking will immediately be greatly reduced.


Five key control areas to ensure quality welds


1. a safe and comfortable working environment for welding

2. applicable welding process protocols and standardised work.


3. high quality welding materials.

4. high performance and stability of welding equipment.


5. the operational skills and experience of excellent welders.
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