A direct comparison of centrifugally cast tubular anodes and die cast tubular anodes

The best way to verify the integrity of the sub-surface structure of a casting is by x-ray. By taking x-ray shots along the length of the casting to ASTM E94 it is possible to view images of the structure. Therefore, generally defining the overall integrity of the casting. X-ray acceptance standards ASTM E186 and ASTM E446 list defects from severity level 1 (an almost perfect casting) down to level 5 (a casting with serious flaws).

 

Many companies are now specifying that anodes should be supplied that pass an x-ray test to level 1, level 2 or level 3 ASTM E186. Although it is not economically viable to carry out an x-ray test on every anode, it is possible to demand that anodes supplied should pass an x-ray criteria level such as level 2 or better and that a percentage of anodes should be tested. An x-ray test might cost approximately $100 per test so it is common for specifications to require 1 in 50 anodes to undergo testing, hence adding $2 to the cost of each anode.

 

What is the significance of defect levels?

By examining the quality of levels 1 to 5 that are displayed by anodes you are able to understand how the theoretical life design of the anode system will be affected.

The table below represents the most up to date summary for assessing the design life against the x-ray level acceptance criteria. Some companies, such as the ENI Group simply state their refusal to accept any anodes that are below level 3 and other companies have based their design life on their own experience and installations.

X-ray Level Design life
Level 1
100%
Level 2
80-100%
Level 3
60-80%
Level 4
20-60%
Level 5
<20%

Level 1

If the x-ray testing determines the casting flaws are level 1 then it is highly unlikely that the life of the anode will be cut short.

Level 2

At level 2 for the acceptance criteria, there are some specific flaws that will influence the overall life of the anode. However, the size and frequency of these flaws are sufficiently small so their existence does not immediately require the need for the casting to be scrapped. The x-ray acceptance criteria should (and does) take in to account both the size, frequency and type of defect present.

Level 3

At acceptance criteria level 3 the casting may not perform correctly. Even though the silicon iron material retains gas porosity, if the anodes are produced to level 3 then there are additional flaws in the manufacturing procedure which are quantifiable and ideally should not be accepted.

Level 4 and 5

This is the same for level 4 and 5 as these flaws are increasing and the design life will be dramatically shortened.

Our testing and results

 

We set out to evaluate the silicon iron castings and the quality and properties for die-cast versus centrifugally-cast anodes through controlled accelerated corrosion tests. These are our key findings.

 

Comparison Results

This x-ray shows a die-cast anode
This x-ray shows our centrifugally-cast anode

In the top x-ray (of the die-cast anode) dark circular shadows depicting sub-surface shrinkage can be seen around the area of the pouring cup, i.e. where the metal has been poured into the anode. These shadows are depicting an area of shrinkage and it is clear from the image that the area around the pouring cup also contains additional fragmented pockets of shrinkage seen as ‘dark patches’ scattered away and around the pouring cup position. In the image, this area has been analysed as a level 3 defect. If an accelerated corrosion test was carried out on the whole anode, then this area would be consumed at a faster rate than the remainder of the anode. Furthermore, these areas around the pouring cup and riser have historically been the source of fissuring and cracking of the anode causing premature failure.

 

Likewise, if a mechanical test bar was machined out of this section of the casting, the results would fall far short of those exhibited by any section of the centrifugally-cast anode. We have retained these pieces for further testing by any interested party, if so desired.

This x-ray shows a die-cast anode

This change in section is an inherent weakness in the design of a die-cast anode because the change in wall thickness means the thicker part of the casting cools more slowly than the narrow section. This slower cooling rate not only causes an inferior grain structure that is almost as poor as sand-cast anodes, but also necessitates an additional riser to help feed the shrinkage that is catalysed from the change in section. The x-ray image of the die-cast anode above shows a serious casting flaw visible as a dark shadow in the connection area and is a real-life sample confirming the difficulties encountered with this design.

 

By comparison, any impurities in a centrifugal casting are thrown to the bore of the casting by application of Stoke’s law and are thus not detrimental to the life of the anode. This is a unique feature of the Centrifugal Casting method and is highly advantageous to the integrity of the casting.

 

It should be noted that the type of defect seen on the x-ray and its position in the casting will further influence the design life. For instance; a linear shrinkage defect in the wall of the casting may well cause a more dramatic reduction in life if it causes the part of the anode to tear along its axial length when in use.

 

Additionally, the centrifugally cast anode utilises a straight-walled anode design that has no change in cross section or thickness at the centre of the anode and no complex arrangement of sand cores (die cast anodes require up to 10 sand cores per anode) which are susceptible to individual discrepancies between every casting, and are an additional expense to the manufacturing process.

 

Jennings Anodes have a manufacturing plant in the UK and a state of the art $2m manufacturing facility at Ningbo in China, where both tubular anodes and solid anodes are made. We have anodes stocked in 2 locations in the USA, utilising purpose-made connectors that have been used in over 1 million anodes over the last 35 years (see g 4 for TA2 and TA5A connectors). We have previously been the only manufacturer exclusively supplying tubular anodes to the Durichlor 51 Anode company. The only tooling that is required to make these connections are 2 torque wrenches (1.2 metres long) that tighten the bolt heads at the end of the connectors, to a pressure of 40lbs (ft/lbs) or 54Nm. These connections can be made in the factory or in the eld.

 

We have 3 XRF chemical analysis machines (in both the UK and China) and our pricing reflects the significant disparity between production costs when comparing foundry production costs in China to those in North America. 

 

You can download the full report of this testing here.

Project: CCell coral reef solution

We’re proud to have been part of an innovative solution to the destruction of coral reefs, working with technology company CCell on its wave-powered coral reef creation.


Why protect coral reefs?

 

Coral reefs form a unique ecosystem that play an important role in protecting coastlines from storms and erosion. According to CCell, more than 70% of the world’s coastlines are being eroded – and it’s thought that the destruction of coral reefs is a major contributor.

Not only that, coral reefs are an essential part of local economies, providing tourism opportunities and jobs. An estimated half a billion people worldwide depend on reefs as a source of income, food and coastal protection.

Sadly, the impact of things like climate change, overfishing and pollution has had serious consequences for coral reefs. The majority of the world’s reefs have already been lost, and it’s estimated that there will be just 10% left by 2040. 

 

The CCell Solution

 

CCell has designed a unique solution to regenerate coral reefs. Using Jennings Anodes components, steel structures form an artificial reef that mimics the force of waves on natural reefs and eventually results in a living reef.

 

The steel structure is placed on the seabed alongside wave paddles that harness renewable electricity from the waves. Power is then distributed across the reef and drives a process that extracts the natural minerals from seawater to create limestone rock around the frames. The structure then provides an ideal base for divers to seed with corals, providing a barrier for the coastline while also re-building a healthy ecosystem. 

How do sacrificial anodes work?

Galvanic anodes, or sacrificial anodes, are used in galvanic cathodic protection systems to extend the life of the steel structure they are protecting. This guide explains what they are, how they work and the different types available.

 

What are sacrificial anodes?

 

Galvanic anodes (also commonly known as sacrificial anodes) are highly active metals that are used within cathodic protection systems. They effectively prevent or dramatically slow down the oxidation reaction or degradation of the parent steel material most commonly seen as rust.  

 

Galvanic anodes are created from a metal alloy with a more negative electrochemical potential than the metal it will be used to protect. This is why they are often known as sacrificial anodes, as the anode metal is “sacrificed” and so the anodes corrode or are consumed instead of the parent metal.

 

How do sacrificial anodes work?

 

Galvanic or sacrificial anodes work because they have a stronger or more negative electrochemical potential than the potential of the metal that they are protecting.

These sacrificial anodes are then said to behave anodically while the parent metal structure is said to behave as a cathode as the anode is slowly consumed through time while the metal structure remains protected. 

 

With the flow of electrons in one direction, the current will flow between the cathode and anode in the opposite direction. 

 

Types of sacrificial anodes

 

There are a variety of different types of galvanic anodes available, suitable for a range of applications. We manufacture four main types of sacrificial anode in three main alloys that have been specifically developed for use in different environments: magnesium anodes, aluminium anodes, water box anodes and zinc anodes.

 

Magnesium Anodes

type of sacrificial anodes

Magnesium anodes are highly electronegative, making them a good option for supplying electrons to more electro-positive steel structures such as pipelines, towers, pilings and bridges. Historically, they have been the most popular anode choice for on-land protection of oil, gas and water pipelines.

 

There are two main grades of magnesium that have different purities and slightly varying electrochemical outputs. The purer grade of magnesium is more problematic to cast and manufacture and ideally requires noble-gas shrouding and other practices to ensure the anode is free from any inclusion, slag, pitting or any other casting defect.

 

More than one million of our magnesium anodes have been installed onto structures across the USA and Canada, and we continue to offer the highest quality anodes available.

 

Aluminium

type of sacrificial anodes 

Aluminium anodes have a slightly lower voltage rate than their magnesium counterparts, but their slower consumption rate makes them ideally suited for seawater and freshwater applications, such as seawater-based vessels, mechanical equipment, marine engineering and harbour facilities, seawater pipelines, ship hulls, ballast tanks, drilling platforms, and wind turbine foundations.

 

Aluminium anodes also benefit from being very lightweight, with a higher capacity than zinc and a relatively low cost per pound. This means they typically have a longer lifespan so are a popular choice for most off-shore applications.

 

As aluminium is not considered a pollutant, they are less harmful to the aqueous environment than other options which makes them well suited for use in seawater, as well as brackish and fresh water.

 

Water Box

 

Available in both magnesium and aluminium types (depending on application), water box anodes are an important component in the protection of almost any enclosed water tank or pressurised vessel. 

Such tanks, including all domestic hot water tanks, a prone to accelerated corrosion within the steel tank and require relatively small anodes to slow down the internal corrosion. 

 

These anodes are often extruded cylinders of either aluminium or magnesium, and are commonly inserted into the tank via a threaded end-cap.

 

Zinc Ribbon

Zinc ribbon anodes offer a flexible, simple, cost-effective and low-maintenance solution to corrosion control.

 

As little to no maintenance is required, zinc ribbon anodes are a good choice for unattended or hard to reach applications, and are often used in underground situations where the anode can be positioned very close or next to the structure it is protecting. More recently, zinc ribbon anodes are also used in the control of AC mitigation. 

 

Comprising an extended ribbon containing a steel wire core, the zinc ribbon anode offers more than 95% current efficiency, making them a highly reliable option. Our zinc ribbon anodes are tested to temperatures as low as 45 degrees below freezing, as well as temperatures that ensure they can operate effectively in the hottest Saudi Arabian deserts. 

Made in Britain: MMO anodes manufactured on site

We are delighted to announced that we are now manufacturing Mixed Metal Oxide Anodes (MMOs) at our specialist UK foundry, following a long-standing tradition of producing high quality anodes in the UK for more than 50 years.

 

Previously manufactured in China, adding the MMO production to the UK allows us greater control over our production flexibility helps us ensure we continue to offer our customers the reliability they have come to expect from Jennings Anodes.

 

What are MMO anodes?

 

MMO anodes provide a stable and durable solution for Impressed Current Cathodic Protection (ICCP) systems. They consist of a titanium base that is coated in a specially formulated mix of iridium tantalum and iridium ruthenium. This coating can be amended to suit different environments or current outputs. The consumption rate of the coating can be extremely slow so that the anodes can be designed to last 30, 40 or 50 years.

 

mmo anodes

Originally developed for the electrolytic production of chlorine and hypochlorites, the exceptional stability of MMO coated titanium anodes means they are now commonplace in cathodic protection applications.

 

Light and easy to install, they are specially formulated to withstand the simultaneous effects of oxygen and chlorine. MMOs are an ideal solution in dilute sea water or fresh water containing low chloride levels. They are also highly durable in acidic media and therefore often used in deep underground applications.

 

Our foundry

 

Operated by a team of experienced engineers, our foundry has the capacity to produce items of up to five meters long and 7000kg in weight – capabilities unrivalled by most foundries. We have more than 400 people working in our foundries and have been making anodes for more than 50 years. 

 

We have supplied castings and anodes to the likes of GE, Tesla, Siemens, Shell, BP, Saudi Aramco, Exxon and many other industry leaders.

 

At Jennings Anodes, we pride ourselves on manufacturing our products to the strictest quality, traceability and international standards.

 

Our casting process ensures optimum anode performance and lifespan. We employ rigorous internal testing standards, in addition to third party testing, to guarantee a high-quality product.  

 

Wherever feasible, each anode is stamped with a unique serial and cast number for quality tracking and after-sales service, ensuring any issues can be easily identified and resolved.

 

How do impressed current protection anodes work?

Impressed current protection anodes are widely recognised as a superior alternative to sacrificial anode systems in solving corrosion problems. In this guide we explain what they are, how they work and the different types available.

 

What are impressed current cathodic protection anodes?

 

Impressed Current Protection Anodes, or Impressed Current Cathodic Protection (ICCP) systems, are a method of corrosion protection that uses a source of electricity to apply an electric current to the anodes that are then used to protect a steel structure, such as a pipeline or steel tower.

 

These systems are generally seen as beneficial for larger structures, or where sacrificial anodes cannot economically deliver sufficient current protection to provide the required cathodic protection output.

 

Impressed anodes are widely seen as a more sophisticated and long-term solution to a corrosion problem. The impressed current system enables the current or driving output to be accurately controlled or varied and it gives the corrosion engineer greater flexibility than a sacrificial anode system.

 

How do impressed current cathodic protection anodes work?

 

Impressed current anodes use and require a source of electricity to “power” the anodes and thus set up the same type of cell that is seen with sacrificial anodes where electrons flow from the anode, through the electrolyte (often the soil) and to the cathode (often the pipeline). 

 

These anodes can be made of various materials, including cast iron, mixed metal oxide (MMO), or graphite. The anode itself can come in many shapes and sizes, such as rods, tubes, wires, plates or even in mesh form.

 

The anode is installed within the electrolyte around the structure to be protected and connected to the positive output, while the structure is connected to the negative terminal.

 

Types of impressed current protection anodes

 

We offer two types of impressed anodes: Mixed Metal Oxide (MMO) and Silicon Iron.

 

MMO

 

mmo linear impressed current cathodic protection anodes

Mixed Metal Oxide anodes (MMO), or dimensionally stable anodes, consist of a rare earth oxide coated onto a titanium substrate. They provide a highly effective corrosion prevention system for various applications and environments, including seawater, brackish water, fresh water, with or without carbon backfill, and also in concrete.

 

Due to the high stability and low consumption rate of the MMO coating, this type of anode has a much longer lifespan than alternative solutions and provides excellent chemical resistance, especially in acidic conditions.

 

Silicon Iron

 

silicon iron impressed current cathodic protection anodes

Silicon Iron anodes, available in both tubular and stick varieties, are a proven cathodic protection solution commonly used in fresh water, seawater, and deep grounded applications.

 

They are a popular choice for cathodic protection systems due to their low specific resistance, suitability for a variety of applications, proven low consumption rate and dependability.