Ask Cougartron | Weld cleaning | Thursday, 15 March 2018

It’s been four months since we launched Ask Cougartron – our new Q/A feature for all of your questions about weld cleaning and surface finishing.

We received a lot of valuable feedback and we would like to thank you for your support.

This time we are talking about neutralization – a topic that is often overlooked within the overall weld cleaning process.

The question we received is related to acid residues that appear on the metal surface after weld cleaning when the neutralization process is not done properly (or at all).

Your question: Why are white acid marks appearing even after the surface was neutralized?

To adequately explain the problem, we must first analyze why neutralization is needed after electrochemical weld cleaning. Then, we’ll provide an overview of the correct and the wrong way to neutralize (stainless steel) welds and surfaces.

What is neutralization and why is it necessary after electrolytic weld cleaning?

Electrolytic weld cleaning is done by using phosphorus-based acids which, with the help of electricity, eliminate impurities from stainless steel and other metal surfaces after welding.

Weld cleaning acids/liquids are mild but often result in recognizable white acid marks appearing on the metal surface – in the absence of proper neutralization.

white acid stains

However, the white acid residue is only a visible symptom of the real problem – increased concentration of the acidic substance on the metal surface. This value is most often measured through the pH scale (0-14) with 7 being the neutral point.

white stains on stainless steel

There are several important reasons for restoring the acid-neutral state of metal surfaces and welds after the weld cleaning process:

  • Cosmetic appearance – white acid marks cover the metal surface making it messy and unappealing which is especially important when talking about metals that are known for their attractive appearance (e.g. stainless steel).
  • Legal regulations – In a lot of situations, regulations require that any surface in direct contact with food or water must be acid free. This also applies to other materials and goods that are susceptible to acidity.

The benefits of the process are numerous but how are stainless steel welds neutralized properly? We discuss the wrong and the right way below.

Neutralization – the wrong way

Neutralization requires the use of specialized neutralizing fluids which are commonly applied to the surface with the help of a sprayer. However, plenty of industrial professionals apply the neutralizer immediately after the weld is cleaned with a brush.

So, the process looks something like this:

  1. Cleaning the weld with a brush and acid/liquid
  2. Application of the neutralizing fluid
  3. Wiping the surface with a cloth

When neutralization is done in this manner, there is a possibility that acid will not be completely removed. The amount of neutralizer applied must surpass the amount of acid present on the surface in order for the process to be successful.

Instead, we recommend a faster and a more cost-effective method to neutralize stainless steel welds and surfaces.

Neutralization – the right way

The essentials of the process remain the same – the only change concerns the timing of the application of the neutralizing fluid.

NOTE: If you work with brushed stainless steel, we recommend using our N5 neutralizing fluid with a specially tailored formula for such surfaces. Our CGT-N1 liquid will not provide an effective neutralizing effect when used on brushed stainless steel.

The correct neutralization process should thus consist of the following stages:

Step 1: Cleaning the weld with a brush and acid/liquid

The weld cleaning brush is used for applying the cleaning liquid to the metal piece and conducting the necessary amount of electricity for successful weld cleaning.

Step 2: Wiping away the excess acid with a cloth

It is advisable to wipe away the excess acid from the surface immediately after weld cleaning so there is less area to neutralize afterwards.

Step 3: Application of the neutralizing fluid

Neutralizing fluids are commonly applied to the surface with the help of a spraying bottle. In this way, the liquid can be evenly distributed over a metal piece.

Step 4: Wipe the surface dry with a new and clean cloth

The surface is wiped with a new cloth since the previous one has acid on it and should not be used again after neutralization.

TIP: Our CGT-N1 neutralizer will create bubbles on the surface while it’s reacting with the weld cleaning acid. The bubbles will stop to form once the process is done and this is when it is safe to wipe dry the surface.

proper neutralization

If you have any concerns and doubts regarding the process, you can always contact us for a free advice. We are happy to help!
Tel: +45 43 20 19 00