Welding Guidelines CuNi

8/12/2019 Welding Guidelines CuNi

http://slidepdf.com/reader/full/welding-guidelines-cuni 1/8

W E L D I N G

G U I D E L I N E S

of

CuNi90/10



Joining:

Metallurgically is solid-solution alloy with no deleterious second phases and experience no

phase transformation during heating and cooling.

Elements such as lead, which may occur as impurities both in the parent alloy and in welding

consumables, are controlled to very low levels so that cracking caused by the presence of

these elements is eliminated. It is also essential that the surfaces adjacent to the joint must be

clean and free from oxide.

Substances such as oil, grease and paint, which may contain sulphur and other deleterious

compounds, must be removed before joining takes place.

To remove oxide and other contaminants, an area approximately min. 10 mm wide on each

side of the joint should be prepared by scratch-brushing with a clean, stainless steel brush

used only for copper alloy. This is followed by degreasing with a non-toxic non flammable

solvent.

No pre-heat is required, but the material must be free from moisture. In cold or humid

conditions, it should be warmed to about 25°C. Interpass temperature should be controlled anshould not exceed 120°C.

The main welding technique is TIG ( Tungsten Inert Gas) for CuNi90/10.

Welding:

Tack welds should be kept to a minimum and as short as possible. Tack welds should be

deposited in the opposite direction to the subsequent weld run and each tack must be

thoroughly cleaned before welding commences. If there is any danger that porosity or cracks

are present in a tack weld, the tack weld must be removed before welding over the area. Use

as many tackwelds as you need, but limit their quantity as down as possible.TIG is preferred for metal thicknesses up to an including 6 mm. TIG welding may also be

used for the root runs in thicker material, the fill-up runs being deposited by the manual metal

arc process.

For CuNi90/10 direct current and a negative electrode is required. The welding power

equipment should work with down slope and high-frequency initiation (pulsed current). The

tungsten electrode have to be sharpened and to stand out of the nozzle for app. 5-10 mm. The

shielded gas is 99,99% pure argon which is also used as the back purging gas (counter gas).

The root pass and first filler pass should be carried out with counter gas. For all further passes

no counter gas is required.

Nitrogen must not be used as it reacts with the deposited metal, giving a porous layer on thesurface of the under-bead.

Weld soundness is dependent to large extent on good gas coverage and arc length. To ensure

good gas coverage it is necessary to protect the weld from all draughts, which would

otherwise disturb the argon shield. After opening of the counter gas valves wait for a few

minutes until the Argon has been replaced by the normal air. The torch has to be held with an

angle of approx. 75° to the surface of the piece to be welded.

The arc should be kept as short as possible. (A rough rule: the distance between electrode and

seam should be the same as the electrode diameter. The electrode should always be held

slightly inclined in the direction of the weld). During the welding process the torch should not

be made to oscillate (drawing line beads). Interruptions during the welding should be kept to a

minimum to limit the danger of pore formation in the endcraters. During the welding processthe welding wire has to be moved in a "Droping"-movement. A stringer bead technique is



used. Runs must be as long as possible to minimise the number of end craters where porosity

is a danger. The protective gas should be allowed to flow for a short period over the deposited

weld metal at the end of each run, to prevent oxidation. In order to avoid oxiditing of the

welding wire, never leave the torch in front of the nozzle.

The use of a crater-filling (down slope) device is recommended to avoid pores and cracks in

the end crater. If such a device is not available, the finish of the weld run should be tapered

and the arc broken at the side of the weld pool.

If the electrode is accidentally withdrawn from the argon while still hot, the highly oxidised

point must be removed completely and reground to shape before welding is restarted.

In the case of an interruption of the weld process oxidised wire ends should be cut off and the

weld seam must be cleaned of oxidation residues.

Pipe welding raises the problem of having to weld in all positions. This contributes to the

choice for welding CuNi90/10.

The root penetration must be 100% without excessive penetration, as any protrusion might

cause turbulence of fluid in service.When TIG welding is used, the bore of the pipe must be purged with argon to prevent

oxidation of the root bead. Removable dams may be used to give economical argon usage, by

restricting the volume of gas necessary. Alternatively, backing inserts may be used, but these

are only acceptable if they can be completely removed from the pipe after welding.

Welding Parameter for welding of CuNi90/10 pipes with additional material CuNi70/30

Wall

Thickness

Diameter of Electrode

mm

Diameter of Welding

Rod mm

Current

Amp

Algon

L/min.

mm Root Interpass/

Top

Root Interpass/

Top

Root Interpass

/Top1,5 1,6 - 1,6 - 55-65 - 6

2,0 1,6 - 2,0 - 60-80 - 7

2,5 1,6 1,6 1,6 2,4 90-100 80-90 7

3,0 1,6 1,6 1,6 3,2 115-130 105-125 8

4,0-5,0 1,6 2,4 1,6 3,2 160-180 150-170 8

Weld Preparation

S< 3mm: square joint

S ≥ 3,0 mm to S ≤ 5,0 mm

α

a s

a = 0 - 1 mm α = 35° - 40°











Welding equipment

Documents

Welding Guidelines CuNi