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06 May 2022

Coated fasteners for heavy industrial use are usually coated for a very good purpose. This is due to the harsh environment in which these nuts and bolts are required to perform. They are often used underwater, underground, or regularly exposed to water in various industrial sectors such as oil and gas, construction, and utilities. When it comes to coating performance, a common misconception in the industry is that the thicker the better. This is far from being true as when the coating thickness is relatively high - this can cause assembly problems, particularly for screwed fasteners with internal drive. A thicker coating may improve its corrosion resistance capabilities, but the excessive layer would stress the fastener, leading to cracking and delamination and will influence the fastener lifetime, appearance, and performance.

Example of corroded Fastener Figure 1 - Example of corroded Fastener
Ref: https://us.sfs.com/learn-more/fine-thread-vs-coarse-thread-screw



The fastener coating and thickness consideration matrix selection can be a complex task. Several factors influence which fastener coating is best for a certain application:

  • - Nature of the Application
  • - Environmental Variables
  • - Structure Material Composition
  • - Expected Stresses

When determining the most effective approach for preventing thread corrosion in fasteners, all technical parameters must be taken into account.

In addition, adhering to thickness helps eliminate waste as only the required material weight is utilized when designing the fasteners, potentially saving tens of thousands of dollars in product costs and ensuring the products are designed with minimum material quantity/weight. Hence it is crucial for the development and manufacturing of the fasteners to find the right balance between coating material and thickness for optimum product outcome. Extensive testing helps manufacturers find that balance, these tests include:

  1. Salt Spray Test – Basic Test
  2. Kesternich Test – Acid Rain Test
  3. UV Test
  4. Humidity Test

SALT SPRAY TEST

Salt spray testing is a technique for determining the corrosion resistance of coatings and materials used in the production of items such as fasteners. An accelerated corrosive impact is performed during salt spray testing to better estimate how effectively the coating protects the metal.


The most common application of salt spray testing is to make rapid comparisons between expected and actual corrosion resistance. In practice, there is only a weak link between the coating's test duration and its actual predicted life. This is because corrosion is influenced by many external causes and is not a straightforward process. As a result, the most effective use of salt spray testing is on samples to determine a pass-or-fail grade and compare it to expectations. This is usually done as part of a quality control procedure or to see how effective a certain production process is.


Salt spray testing is quick, repeatable, and reasonably inexpensive, salt spray testing has long been the standardized corrosion test method. Salt spray tests are carried out in a sealed chamber. A spray nozzle is used to apply a saltwater solution to a sample. A corrosive experiment is simulated with this intense saltwater fog. The appearance of oxides is examined over a length of time, which is based on the corrosion resistance of a product. The longer it takes for the oxides to emerge, the more resistant the product is. For certain coatings, testing can take anything from 24 to 1,000 hours or more.


KESTERNICH TEST

In critical environments, the salt spray test cannot be the only test used to determine corrosion. As a result, we advocate performing further testing to ensure that the chosen surface treatment is appropriate for the location in which the product will be utilized. The sulfur dioxide test (SO2 test, commonly known as the 'Kesternich' test) is a useful laboratory supplement. The test aims to simulate acid rain conditions by subjecting test specimens to a sulfur dioxide atmosphere as well as condensing moisture for the purpose of evaluating rust/corrosion characteristics.


The test is usually completed in a 24-hour cycle which is divided into two parts:
First, Warm-Up Section 1: 8 hours at 40±3 °C (relative humidity 100%).
Followed by Cooling Section 2: 16 hours at 18 to 28 °C (max. relative humidity 75 %).


The samples are placed above the water level and a predetermined volume of distilled or deionized water is poured into the test chamber's floor pan. The chamber's entrance or hood is firmly closed and hermetically sealed for safety reasons. A set volume of Sulphur dioxide, usually either 1 L (0.33%) or 2 L (0.66%), is then delivered into the chamber.


UV TEST

In Ultraviolet (UV) testing, the test is performed at ambient temperatures, the purpose of testing is to observe how a material would react to long-term sunlight exposure. Where the source of irradiation is a UV lamp that emits wavelength, where the strength of the wavelength is specific to the fastener’s actual application and exposure requirements. After every 24 hours exposure the samples are inspected and any degradation of coating due to long term exposure to UV radiation is investigated. Fluorescent UV testing devices intend to accelerate and reproduce the weathering effects that occur when materials are exposed outdoors in actual use. Giving a real indicator to the product performance over its expected lifetime.

HUMIDITY TEST

A humidity test is a corrosion analysis technique that helps determine corrosion rates in materials. This test exposes the material to a variety of environmental conditions and corrosive agents in order to investigate the influence of corrosion on diverse industrial materials. Humidity and fog are regulated specifically for corrosion study in a humidity test. From electrodeposited paints or coatings to copper tube systems, this is employed for a wide range of products. Humidity tests are commonly used to determine the corrosivity of materials or the effects of substances such as residual pollutants.


The cyclic humidity test is a variation of the test that is used to simulate excessive heat and humidity exposure. A dependable feedback controller and humidity sensor are required in the test cabinet.


Various things can be explored using this test, including parameter shift failures, mechanical failures, coating degradation, and other elements that are all vital in sustaining operation quality.


BOTTOM LINE

Inadequate coating thickness would result in reduced cohesive strength, brittleness where protection is needed the most, and the fastener would be exposed to corrosion. When anti-corrosion coating is applied to the optimum thickness, the coating's protective characteristics are optimized, resulting in a highly durable surface. That is why we focus on reducing corrosion risks to our customers by applying the detailed testing measure and acceptance criterion for our products. We provide a comprehensive choice of unique anti-corrosion fasteners at Engineering Edge that are proven to operate in corrosive environments for various industries.


At Engineering Edge, we guarantee that each fastener undergoes extensive research and testing. Each fastener passes the most detailed quality checks to exceed your expectations and perform for a minimum number of years before becoming structurally unreliable due to premature corrosion. We offer a variety of products such as:

  • - Premium retail fastener of choice by builder's mart - TAPPERMAN® which offers various display and packaging solutions for building material retailers.
  • - DYNO® Fasteners, Quality compliant structural fasteners for peace of mind.
  • - Innovation filled anti-corrosion fasteners for hostile environments - CORROSHIELD®. Years of research has allowed us to accurately design various coating options using different technology to cater to a wide range of hostile environment.
  • - EN 10204 Compliant (Optional) applicable to all screw ranges - TAPPERMAN®, DYNO®, CORROSHIELD®.

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