Simple Weld Testing of Custom made Car and Motorcycle Parts

At Flash Customs we use a variety of weld testing methods to determine the  quality of weld as required on a custom made item.

We manufacture custom made 1 off items such as Fuel, oil and water tanks, water pipework, radiators, inter-coolers, modify cast aluminium and steel sumps, cam and rocker covers, oil, fuel, water take off stubs etc.

Many of the above need to be “leak tested” in some format. This can include a pressure and or weld test procedure to ensure that no leaks are present. No one wants a nice new shiny alloy fuel tank fitted to their pride and joy that they have spent many hours building or modifying only to find once filled with fuel a puddle appears on the floor under the vehicle!    – dangerous and expensive.

Having completed more than 1200 tanks, radiators, inter-coolers, sumps etc we have only ever had 1 tank with a small pin hole that got through our testing. (a pretty low percentage I think you`ll agree).

To give you an example of a testing method I will explain the process we went though when testing a recently chopped and modified cast aluminium sump.

For this Job we used a Non Destructive Testing Method Called ” Dye Penetrant Testing”

Chopped Sump before welding back together

Above picture showing chopped sump ready for infill plates and welding back up.

Sump after welding

Image above – Once welding was completely finished, testing to check for leaks could commence.


Initially a quick clean over with some scotch brite to remove any oxide and a visual inspection of all the welds gave a good idea of the integrity of the welds and potential areas for any leaks could be identified.


Once the welds have had any surface oxides removed we can spray a coat of  “cleaner” onto the tested areas, this can be wiped off with a soft cloth leaving a grease / oil / fingerprint free surface for the Dye to be painted or sprayed onto.


Dye now usually comes in a spray can, NOTE – ensure whilst using testing products like this you ensure good ventilation as the fumes can be dangerous and overwhelming if not. A very thin coat of dye needs to be evenly applied to the surface of the weld and left to soak in for a few minutes.


The image above shows dye that has been left for a few minutes and is now ready to wipe off the welded area with a clean lint free rag. Wiping the excess off the surface should only leave dye residue hiding in surface defects, pin holes, cracks etc.


Once dye residue has been wiped off with a rag, it is now important to wipe over the surface again with a lint free rag that has had “cleaner” sprayed on it. We do not “soak” the rag otherwise this may “wash out” any dye sitting in surface defects, thus rendering the test inaccurate. The idea of wiping off any excess with a rag sprayed with cleaner (not soaked) is that it will remove any thin coating of dye on the surface that may be left, this will then allow a much clearer test.


Now we have a clean weld area again we can complete the test by spraying “developer” evenly across the test area.

This will leave us with a thin coat of “chalky” material on the surface of the test area, this will soak up any dye that is hidden from view in any surface defects and show up as a red line or dot in the developer. Any such areas where dye can be seen to be drawn out of surface defects and shown in the developer are a cause for concern which will need further investigation. The image shown above shows a nice clean “dye” free “developed” test. As does the image below.

You may well ask then what would it look like if there where to be any defects visible, the image below shows a small pin hole in the crater of the weld (immediately in the middle of the picture). This may need further investigation as a small pin hole in the crater of a weld could be the source of a “stress fracture” as it may be slightly weaker than the surrounding area of weld.

Just to verify or prove that a pin hole is indeed going to be an issue, on a job like this oil sump we would look to fill with a mixture of waste oil and thinners, leave for an hour and then see if any “staining shows through around the suspect area.

The image above shows a suspect area shown up by “dye penetrant” testing, after which the sump has been filled with an oil / thinner solution. You can clearly see an area of staining where the liquid has soaked through the defect that obviously was not just a “surface” defect but indeed went through the thickness of the sump wall.

Below shows the repaired defect ready for testing again.

The weld was cut back with a grinder and re-welded to ensure a full repair. The complete test procedure would then be carried out on this area as a double check that the repair had been successful.

Just to show my point above you can see where the dye has not been “cleaned” fully from the internal sump plug thread. Once “developer” had been sprayed on the surface the dye had been drawn out of the threads and starts showing on the bottom edge of where the thread breaks out to the surface.

DYE PENETRANT testing is an ideal way of “non destructive” testing welded items and as a general rule of thumb gives a good guide to weld quality. It could be presumed that if there were surface defects showing in the weld then defects may also be present under the surface where the eye cannot see!

A further point to consider is that typically an oil sump like this will expand as the hot oil warms the aluminium and this could exaggerate any potential defects and cause a leak that may not be present or show whilst the sump is “cold”.

In industry there are of course many other methods of NON DESTRUCTIVE testing such as , magnetic particle, fluorescent particle, ultrasonic and xray to name but a few. Obviously these tests all get more complicated, incur added  cost and many need to be carried out by specifically trained staff.

Of course the easiest and cheapest Non Destructive test is “visual” – simply looking over the weld and scrutinising it for any potential suspect areas.



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For all your Custom Car & Motorcycle Parts Manufacture and Welding / Repairs
Don`t forget to email or call us for all your custom made 1 off bespoke items.
Thanks for reading our blog – we hope this has been of use to you.
Recommended sites
FLASH CUSTOMS – Specialist Custom Car & Motorcycle Parts
Automotive LED Lights – Car & Motorcycle LED Lighting Solutions
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Time to get the TIG Welder revved up, alloy fuel tank for rotrax to assemble & weld

Get up and running again this weekend, a nicely cut and pressed alloy tank for a ROTRAX Kit Car is calling.

Area above that we have free to fill with an aluminium fabricated fuel tank, size, shape, capacity, design, filler, pick up and breather position to consider as well as stages of manufacture. This is gonna be a wide, flat tank to sit up inside the chassis and care to add a sump in a position to miss the diff at max suspension compression is required.

Keep an eye on our blog for pictures of build.

See videos of the build –


For all your Custom Car & Motorcycle Parts Manufacture and Welding / Repairs
Don`t forget to email or call us for all your custom made 1 off bespoke items.
Thanks for reading our blog – we hope this has been of use to you.
Recommended sites
FLASH CUSTOMS – Specialist Custom Car & Motorcycle Parts
Automotive LED Lights – Car & Motorcycle LED Lighting Solutions
Loaded Wallet – Discount and cash back offers
Cash Back – Cash Back & Money Saving offers