Copper Nickel Welding Guide

Introduction

Are you looking for the copper nickel pipe welding procedure?

If so, then you are reading the right guideline about it.

This book will provide a basic overview of the welding process and an insight into copper-nickel alloy welding operations.

Copper-nickel Welding

Chapter 1: What is Copper-nickel Welding?

Copper is a metal; it is orange in color, a great conductor of electricity and very malleable (soft) in its pure form. It is used in many applications and is abundant in the earth’s crust, which makes it easy to mine. Copper’s periodic table is ID is Cu.

Nickel is a transition metal; it is silvery yellow in color, highly resistant to corrosion, strong and weak in its pure form. Nickel is used as an alloy in metal fabrication for its amazing attributes that make combining it with other metals a major contributor to the resistance of the alloy to corrosion. Nickels periodic table ID is Ni.

Copper-nickel alloys are amazing alloys used for sea water application. This means that they are found in many environments where pipes and heat exchangers are required to be submerged underwater.

The Finished Copper Nickel Welding Products

Copper-Nickel alloys have been around for 50 years and were originally used in offshore pipework. Over time their application has been expanded to include parts in sea ships, specifically in condenser/heat exchangers on ships and are used in desalination, power plants and offshore fire water systems, and for the sheathed splash zone protection of oil and gas platform legs.

The manufacturing of Copper-nickel alloys is not a complicated process but does require a high degree of cleanliness in the fabrication process. They are easy to machine, cut and process as well as to weld.

After welding  with copper nickel pipes, copper nickel flanges , copper nickel pipe fittings and other pipe component , it can form a strong copper nickel pipeline used on marine , offshore and other industies.

This book will look at the welding process and provide insights into the different types of welding processes that are used to weld Copper Nickel alloys.

Chapter 2: What Alloys are used?

Marine service uses two grades of Copper-nickel alloys, and these are 90-10, which means that 90% is copper and 10% is nickel, or 70-30, which means there is only 70% copper and 30% nickel.

The main differences between the two alloys are:

• 70-30 is a stronger alloy and has better resistance to seawater flow
• 90-10 is less expensive due to the lower nickel content and provides a good service alloy

Both alloys will contain small parts of iron and manganese, which are added during the alloying process to provide extra strength and resistance to seawater corrosion.

Table 1. Shows the Standards of the two alloys,

ASTM, ISO, and CEN are synonyms for international standards organizations that designate how alloys are identified.

UNS Chemical Composition (%) of 90-10 and 70-30 Alloys for Welding Applications

In Table 2,  we see how the welding alloys require limits to optimize welding strength and performance. The Unified Numbering System is an international standard numbering system that makes all alloys conform to the same specifications. This is important for companies when buying the nickel-alloy products and welding apparatus so that these products possess no deviations from acceptable ranges.

Table 2

Here at ShiHang we provide a comprehensive supply of different alloys, you can view the chemical composition of each one we have in this link.

Typical Mechanical Properties of Annealed Copper-nickel Sheet and Plate

Table 3 shows how copper-nickels are stronger and more resistant to corrosion than just plain copper, but due to the softness of copper are lower in strength than steels. Their ductility (ability to transfer electricity), toughness and malleability are excellent. Copper-nickel alloys do not become brittle when they get cold, and they even retain their mechanical strength at cryogenic (extremely frozen) temperatures. In Table 3,  you can see the difference in their mechanical abilities at room temperature ranges; these will change slightly when the environment is below freezing.

Table 3

Typical Physical Properties of Copper-nickels and Steel

In table 4 you can see a comparison of the properties of the alloy versus plain carbon steel. One of the main characteristics you will notice is that Copper-nickel alloys are not magnetic. Their thermal heat transfer (how heat travels through them) is lower, so when combined with their coefficient of linear expansion, makes them less susceptible to cracking due to changes in temperature and pressure.

Table 4

General Handling

As a rule, cleanliness is mandatory; it is extremely important to ensure that the areas where the manufacturing and welding of Copper-nickel alloys occurs are free of contaminants. are free from contaminants. Contamination will change the chemical structure of the alloy, and this can lead to cracking and porosity, as well as reduce the corrosive resistance of the alloy.

This means that fabrication, as well as welding, should be done in a Copper-nickel environment only, and all materials must be handled with care so that they do not become dirty with oils, liquids and other contaminants that can be applied to the surface through touch.

When welding, grease, and paint must be clear off all surfaces, and all marks and signs from permanent markers, pencils and crayons have to be removed. It is advised you use a stainless-steel brush to clean surfaces properly. Grinding discs should be alloy specific and not interchanged between different metals.

All pipe openings have to be protected to prevent any contaminants entering them or covering a surface area before welding.

At ShiHang we provide the cleanest and most sterile environment for all your products.

To form an easy copper nickel pipe line , some component as below are need:

• copper nickel pipe
• copper nickel flanges ( seven main type of copper nickel flanges – composite weld neck flanges , composite slip on flanges , weld neck flanges , slip on neck flanges , socket weld flanges , threaded flanges and blind flanges )
• copper nickel butt weld pipe fittings ( elbow , tee , reducer , saddles , end cap)

They form an easy copper nickel pipe system after welding.

Chapter 3: Introduction to the different Welding types

Copper-nickel alloys are easy to weld. Due to the alloys, simple metallic structure welders do not need to pre-heat surfaces or provide any post-welding treatments. The only basic requirement is to assure that all surfaces to be welded are clean from contaminants.

Welders must be proficient in the process that is being applied. This means that your welders must be certified, have experience and can perform all the necessary pre-welding requirements. In all instances, a welding procedure specification (WPS) should be prepared for all procedures.  This will assure you that you are conforming to the insurance and inspection bodies that regulate and certify welders.

The most popular form of Copper-nickel welding is tungsten inert gas (TIG), which is also known as the gas-shielded tungsten-arc (GTAW) process. Let’s take a look at the four types of welding and the brazing process.

• Tack Welding

No matter which method of welding you choose, you need to tack your surfaces since Copper-nickel alloys tend to distort. This means that you need a fixture to limit the movement of the surfaces to be welded. These fixtures are called tack welds, they are like spot welds of material, and they need to be positioned to create a uniform gap between the surfaces being welded together.

The position of a tack is around half the spacing used in conventional welding. Once tacks are in place, the surfaces need to be cleaned with a steel wire brush, and all contaminants need to be wiped away.

• Preparation for Welding

The wire used in Copper-nickel welding is around 3mm thick for optimum performance and has a square butt preparation. Do not perform autogenous welding, this will result in porous weld joints, due to the structure of the alloy that contains no deoxidizers.

If you decide to weld with a thicker rod, then you will need to bevel a V into the surface, this bevel will be around 70°. Copper-nickel alloys are not as fluid as carbon steel, so you need a wider angle for movement, add to this the need to manipulate the molten material with the copper nickel welding electrodes to assure ample fusion with the side walls.

Copper-nickel welding is best performed vertical-down, this makes the process easier and allows a larger deposition of material along the weld. While large or complex jobs might require differing positions, sub-assemblies should favor a down-hand welding position.

Due to the nature of the alloy, you don’t need to pre-heat the surfaces. The only time you would heat up a surface is to assure it is completely dry. You need to maintain the interpass temperature below 150°C to assure no micro fissuring.

Always store your materials and jobs in a clean area. Make sure all are dry if necessary heat up all surfaces and consumables to dry them out before use. Do not allow anyone to touch the surfaces with their bare hands since oils on the skin can react with the surface. Make sure you check the weld join area’s very well before starting to weld. The optimum area that should be clean is 10mm wide on either side of the weld join area.

• Manual Metal Arc (MMA or SMAW)

SMAW Welding

Shielded metal arc welding (SMAW) is also known as manual metal arc welding (MMA) in a manual arc weld that uses a consumable electrode with a flux.  It can be electrode positive, negative, and use alternating current.

Most rods exposed to moisture cannot be recovered.

Electrodes are usually smaller than their carbon steel counterparts, and welders need to take this into account when considering weaving. Manipulating the electrode for weaving should not be more than three times the width of the electrode.

Don’t use a long arc; this will reduce the quality of the weld resulting in porosity as a result of the weld reacting with the atmosphere.

• Gas-shielded tungsten arc (TIG or GTAW)

Gas-shielded tungsten arc (TIG)

Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) is arc welding that uses a non-consumable tungsten electrode to produce the weld.

The main difference between TIG and MMA is in the versatility of separating the arc from the filler metal. This allows for better flexibility and is an advantage for complex shape welding. This includes joints and or when inserting root runs into thicker joints is required. TIG is the preferred welding process for thin-walled pipes.

Here are some key considerations when using TIG:

• Use a backing gas, such as Argon when performing a pipe weld root run
• argon is the preferred shielding gas
• Use a short arc, which will enable the shielding gas to protect the weld pool.

TIG (GTAW) welding 90-10 Copper-nickel assembly. Note baffle for backing gas supply at root run stage

• Gas-shielded Metal Arc (MIG or GMAW)

We will not go into too much detail here since this process is capex intense and is not really used much in Copper-nickel processing. In general, the difference between MIG and TIG is in the machinery used to perform the action, and the atomization of the solid wire electrode process. Again, since this system is not used widely, we will not discuss it here.

Copper nickel flanges weld with copper nickel concentric reducer

• Brazing

Brazing is not welding; it is the application of a filler metal through direct melt onto a surface. Basically, you hold a brazing torch in one hand, a copper nickel brazing rods of metal in the other and the heat from the torch melts the wire onto the surface you want to connect. Since the filler metals is a lower temperature material than the two surfaces it is connecting, the surfaces are not affected by the process, and the metal acts as an adhesive, rather than becoming part of the surface itself. Brazing requires extreme cleanliness. The types of filler metal used in brazing include:

• Copper
• Copper-silver
• Brass
• Gold-silver
• Silver
• Nickel alloy

Brazing also has a number of different approaches, these include:

• Torch Brazing
• Dip Brazing
• Furnace Brazing
• Infrared brazing
• Salt-bath brazing
• Induction Brazing
• Exothermal brazing
• Resistance brazing

However, in our article here we are only referring to standard torch brazing.

• TIG Welding vs. Brazing

You might ask why to prefer brazing over welding or vice versa, well here are the reasons for choosing either one of the processes.

• Assembly Size
• When you have a large assembly, TIG is preferred. This is because brazing requires heat transfer over a wider area and that can impact the performance of brazing with large assemblies.
• Metal Thickness
• Brazing is a preferred choice for thinner metals. TIG comes into consideration when the thickness of the metal is half an inch or thicker.
• Joint Shape
• Linear joints are better suited to brazing while fusing spot joints are more suitable for TIG.
• Material Types
• It is always preferred to use brazing when trying to connect two different materials. Welding can be more expensive and also more complex.
• Appearance
• Welding can often give irregular beads, so brazing is used if you want a better and smoother result.

Chapter 4: What are Welding Consumables

There are a number of consumable products being used in Copper-nickel welding, and they include flux-coated electrodes and bare wires. These items are made to specifications that meet international standards. These specifications include a number of different compositions, which are shown in Table 5.

Table 5 – Welding Consumables Specifications

AWS – American Welding Society, Bs – British Standards Institution

Copper Nickel Welding Rods

In most cases the consumables are made to the same specifications of the target alloys. However, there are differences in the level of corrosion resistance with alloys in the 90-10 range. Due to the poorer quality of resistance in 90-10, it is best to use 70-30 consumables copper nickel welding rod. As seen in Table 5, additional elements are added to the consumables to make them better conductors for welding, brazing and provide better resistance after being applied.

Normally , the dimension of copper nickel welding rods is according to the copper nickel pipe specifications. The common size of tig copper nickel welding rods is 2.0mm, 2.4mm, 2.5mm and 3.2mm.

When welding different metals together, such as steel to Copper-nickel the consumable will have 65% nickel content. This is used to assure a higher iron dilution from the steel during welding and prevents cracking.

Most of the consumables contain small parts of titanium which are added to enable reaction with the nitrogen and oxygen-rich atmosphere. Porosity after welding is usually due to an excessively long arc during welding., bad surface cleaning, moisture on the weld during the preparation, or when using unclean or wet electrodes.

Chapter 5: A Look at Post-Weld Treatment

One of the major advantages of Copper-nickel welding is that there is no need for post-welding heat treatment of the surfaces. The welder or finisher needs to clean off any spatter from the surfaces, as well as remove all slag from the joints. Slag accumulates during the manual metal arc processes. The best way to clean slag is either with a stainless steel brush or with a rotating flap wheel.

When finishing a weld joint, it is best to reverse the electrode direction to remelt the start points or the crater which is found at the end of the run. Between runs, the welder must remove all slag, and other contaminants by brushing the surface with a stainless steel brush.

• 5.1. The Welding Inspection Process

All weld joints should be inspected by eye for any defects; these include non-conforming weld contours, cracks, undercut, lack of fusion and penetration.

The next inspection must be done with a liquid dye penetrant that can help detect any surface defects and porosity.

The third and more critical inspection will use radiography for parts that would be sent into deep waters and are considered to be extremely vulnerable, and/or critical.

• 5.2. Understanding Bend Tests

A bend test is a process in which a weld is stressed to prove its quality. A weld is either a strip of metal that has been “glued” to another strip of metal using a similar or identical material; this is brazing. Or, a weld is when two surfaces have been fused together with heat and an identical material, this is arc welding. A bend test is when two strips of metal are fused or glued together and then bent along the weld to see if the weld remains intact. The test also shows whether the heat affected zone (HAZ) retains the metals base mechanical properties.

There are two bend tests, and these are performed by a quality inspector.

A longitudinal bend test is performed on the test specimen. This test is extracted in the longitudinal direction of the sample piece. The longitudinal tensile test is the preferred tensile test performed on Copper-nickel alloy welds

The less popular transverse tensile test is performed to measure transverse tensile strength, yield strength, proof stress, elongation, and reduction of area. The transverse tensile strength is very important mechanical property in pipes and Hoop’s stress calculation.

• 5.3. Matched Mechanical Properties

Bend tests are used to test the mechanical properties of the two pieces welded together. In some instances, the strength of the weld can outmatch the strength of the objects welded together. This issue arises when the welding material is not less than, or identical to the base material characteristics.

What most tests look for is the base metal being stronger than the weld, but not by too much. The weld should match the mechanical properties of the base metal very closely. In many cases, this is not an issue, but with deep sea welds, and objects that are put under extreme stresses due to pressure, and heat or cold, the weld should not be significantly different. Otherwise, they will crack.

Since copper-nickel welding usually uses a different weld metal to the base metal, such as 70-30 with 90-10, then longitudinal testing is mandatory.

Chapter6:Checklist for Copper-nickel Welding

Copper-nickel welding requires conformity to standards and high cleanliness; it is important to assure this at all times. Here is a basic checklist performed for all welding processes.

• Only source your base materials (copper-nickel alloys) from a reputable supplier that meets international standards.
• Assure that your coordination and plant site maintain the highest levels of cleanliness to assure a complete supply chain and production process clean environment.
• It is advisable to use 70-30 copper-nickel consumables for all welds including 90-10 and 70-30 copper nickel
• When welding steel to copper-nickel, use 65% nickel-copper consumables.
• Make sure you do not exceed maximum stress limits for the alloys.
• Try to avoid stress concentrators raisers such as sharp-angled bends in pipe systems
• Do not use polluted water or other contaminated sources of water during the welding process.
• If an extra safeguard is required, add ferrous sulfate.
• Where high resistance to biofouling is required, electrically insulate copper-nickels from less noble alloys.

Conclusions

Copper-nickel alloys or cupronickel has been known to man for over a thousand years. It was originally known as white copper to the Chinese as far back as the third century BCE. The alloy is white even though it has a high content of copper. The 70-30 alloy was widely used before the 1950’s, however with the accumulated years of its use, and the scientific method used in the modern ear, a 90-10 alloy was found to be better suited for seawater purposes.

Copper-nickel alloys are welded today in much the same way they welded 50 years ago. Fluxes and machinery have advanced in technological diversity, but the alloy and its applications remain the same.

As with every different alloy and metal, welders have to undergo training to be effective in working with this alloy. Due to its abundance of oil rig platform cladding as well as underwater piping, hyperbaric welding is commonly used as a form of welding deep underwater. Understanding the nature of the metal in every environment is an important factor in successful welding, and great welders can be found working in the most bizarre locations.

Sources

• Copper-nickel Alloys: Properties and Applications. NiDI/CDA Publication TN 30. 1982
• 90-10 Copper-nickel. CDA Publication No 118. 1997
• 90/10 and 70/30 Alloys Technical Data. CDA Publication TN 31. 1982
• Guidelines for the Use of Copper Alloys in Seawater. A Tuthill. Nickel Institute Publication 12003
• The Application of Copper-nickel Alloys in Marine Systems. Technical report (compendium) available from CDA Inc
• The Corrosion of Copper and its Alloys: A Practical Guide for Engineers. Roger Francis. NACE International. 2010
• Copper Alloys for Marine Environments. CDA Publication No 206. 2012
• Joining Copper-nickel Alloys. R E CDA Inc Seminar Technical Report 7044-1919. The Application of Copper-nickel Alloys in Marine Systems. 1992
• Brazed Copper-nickel Piping Systems. CDA Inc Application Data Sheet 701/5
• Welding Copper-nickel Clad Steel. CDA Inc Application Data Sheet
• Copper Advantage: Guide to Working with Copper and Copper Alloys.
• Copper Development Association Inc Publication. 2010.
• Welding Technical Aspects of welding copper-nickel alloys, G. Van Dyck, J. C. Thornby and H. de Vries, Rev. Soudure Lastijdschrift, 1976, No. 3, pp. 133 – 140 and pp. 157 168
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• Welding Solid & Clad copper-nickel alloy plate, M. Prager, L. K. Keay & E. W. Thiele, 60th AWS Annual Meeting, Detroit, April 1979, Welding Journal, May 77, Sept. 78 & July 79 (CDA Inc. USA Technical Report)
• Welding Products for Copper-nickel Alloys, Henry Wiggin & Co Ltd. 1979.