What welding procedures are recommended for eemua 144 234 cuni pipe?

Welding is the make-or-break step for any copper-nickel piping system built to EEMUA 144 and EEMUA 234. The alloy's high thermal conductivity, sensitivity to heat input, and tendency to absorb gases mean that an average steel procedure will not work. This guide walks through the welding procedures that are actually recommended for EEMUA 144 234 Cuni pipe on offshore platforms, in marine & shipbuilding systems, and in seawater cooling loops, and shows how to match each procedure to the pipe you have on site.

The recommendations below are written for project engineers, welding supervisors, and QA inspectors who need a practical procedure they can apply to a real WPS (Welding Procedure Specification) and a real PQR (Procedure Qualification Record). All product and material references are consistent with EZ Steel Industrial's Cuni pipe range.

1. Why EEMUA 144/234 Cuni Pipe Needs Special Welding Procedures

EEMUA 144 covers 90/10 copper-nickel (UNS C70600, CW 352H) tubes and fittings for offshore use, while EEMUA 234 covers 70/30 copper-nickel (UNS C71500, CW 354H) tubes for the same duty. Both standards call out the same root cause of in-service failures: the welding procedure, not the pipe itself.

Three properties drive the procedure:

• High thermal conductivity. Heat leaves the weld pool faster than in carbon steel, so you need higher heat input per unit length to maintain fusion. At the same time, too much heat causes grain growth and distortion.
• Susceptibility to porosity. Hydrogen, oxygen, and sulphur in the arc atmosphere or on the parent metal become gas pockets in the solidifying weld. Pure shielding gas and clean surfaces are non-negotiable.
• Risk of hot cracking and iron contamination. Sulphur and phosphorus over the EEMUA limit, or iron picked up from carbon-steel tools, both attack the joint in service.

A good procedure balances those three risks. The sections below give the recipe.

2. Pre-Welding Preparation: The Procedure That Decides Weld Quality

A EEMUA 144/234 procedure always starts with a documented preparation step, not with striking the arc. The items below should appear in the WPS as mandatory pre-weld checks.

2.1 Material verification

• Confirm the alloy: 90/10 (C70600) or 70/30 (C71500). The two grades are not interchangeable for filler selection.
• Cross-check the heat number on the pipe with the mill test certificate (EN 10204 3.1 or 3.2).
• For 70/30 service, the certificate should show nickel at 29-32% and iron at 0.4-0.7% for seawater resistance.

2.2 Surface cleaning

• Degrease the joint area, at least 25 mm on each side, with acetone or an approved solvent.
• Remove oxide films with a clean, dedicated stainless-steel brush. Carbon-steel brushes are forbidden — they leave iron particles that cause pitting.
• Store filler rods in a dry cabinet; moisture in the flux coating or on the wire is a direct source of porosity.

2.3 Joint fit-up

• For tubes above 2 mm wall thickness, machine a V-groove of 30°-40° with a root face of 1-2 mm.
• Keep the root gap at 1.5-2.5 mm for TIG root passes. Too tight causes lack of fusion; too wide wastes filler and increases distortion.
• Misalignment across the joint should not exceed 10% of the wall thickness; EEMUA 144/234 allows no offset that creates a stress raiser.

If any of the above cannot be met, stop and raise a deviation report. A clean, well-aligned joint is the single biggest predictor of an in-service weld that passes hydrostatic test.

3. Recommended Welding Processes for EEMUA 144/234 Cuni Pipe

EEMUA 144/234 do not mandate a single process, but they do restrict the choice. The four processes below are the ones you will see in qualified WPSs on offshore and shipyard projects.

3.1 TIG (GTAW) — the default for root passes and thin-wall pipe

TIG is the recommended process for root passes, all positions, and pipe wall thickness up to about 4 mm. The non-consumable tungsten electrode gives a stable arc, the operator controls heat input by foot pedal, and the gas coverage protects the weld pool from atmospheric contamination.

• Electrode: 2% thoriated or 2% lanthanated tungsten, 2.4 mm for most tube sizes.
• Shielding gas: argon 99.99% minimum, 12-15 L/min through the torch.
• Backing gas: argon 99.99% at 6-10 L/min on the root side. Oxygen or nitrogen backing is not acceptable.
• Filler: ERCuNi (AWS A5.7) for 90/10, ERCuNi for 70/30 with higher nickel content.
• Interpass temperature: keep below 150 °C; use a contact pyrometer to confirm.

Hold a short arc (1.5-3 mm). Long arcs draw in atmosphere and cause porosity. Use current ramping at start and end to fill the crater.

3.2 MIG (GMAW) — for fill and cap on thicker pipe

MIG is recommended for fill and cap passes on pipe 4 mm and thicker, and for long production runs where deposition rate matters. Use a push-pull torch to feed the soft ERCuNi wire without kinking.

• Wire diameter: 1.0 or 1.2 mm ERCuNi.
• Shielding gas: argon with 1-2% CO2 or argon with 0.5-1% O2. Do not use CO2-rich mixes; they oxidise nickel and create slag.
• Voltage: 20-24 V; wire feed speed: 4-7 m/min, tuned to the actual current.
• Stick-out: 12-18 mm. Longer stick-out lets argon coverage collapse and pulls in oxygen.

MIG on Cuni is more sensitive to wind and draught than on carbon steel. Set up wind shields when working on deck.

3.3 Pulsed MIG and pulse TIG — for critical service and high-alloy welds

When the WPS calls for tight heat input control — for example, on thin-wall condenser tubes or where distortion must be minimised — pulsed MIG and pulse TIG give a stable arc at lower average current. Pulse parameters are typically specified by the machine manufacturer and qualified on a test coupon before production welding.

3.4 When to avoid other processes

• Shielded metal arc welding (SMAW / stick) is generally not recommended for EEMUA 144/234 pipe. The rutile or basic coatings on standard electrodes introduce hydrogen and slag, both of which are difficult to remove from a Cuni weld pool.
• Oxy-fuel welding and brazing are not acceptable for pressure-retaining pipework in offshore service. They are sometimes used for non-critical trim, but never for the pressure boundary.

If the project specification demands a process outside this list, qualify it through a separate PQR — do not assume it transfers from carbon-steel procedures.

4. Filler Metal and Shielding Gas Selection

Filler and gas choice is the most common place where site teams get the procedure wrong. Use the table below as the starting point for your WPS.

A few rules that are easy to forget in the workshop:

• Keep filler metals in original packaging until use. Re-bake or discard rods that show surface oxidation.
• ｒｅｐｌａｃｅ shielding-gas cylinders when pressure drops below 20 bar; low-pressure flow is unstable and lets in air.
• For root-pass back purge, use a separate argon line with a flow meter, not the torch gas split.

When the pipe transitions to a different alloy — for example, where a Cuni line meets a B167 Ni-Cr-Fe alloy tube in a power-plant feedwater system — the filler and heat input must be qualified for the dissimilar joint, not just the parent alloys.

5. Welding Parameters and Heat Input Control

Heat input is the single most important number to record on every Cuni weld. EEMUA 144/234 do not give a single maximum value, but industry practice is to stay within 1.0-1.5 kJ/mm for TIG root passes and 1.5-2.5 kJ/mm for fill and cap.

Heat input is calculated as:

Heat input (kJ/mm) = (Voltage × Current × 60) / (Travel speed × 1000)

Worked example for a TIG root pass on a 3 mm wall 90/10 tube:

• Current: 90 A
• Voltage: 12 V
• Travel speed: 80 mm/min
• Heat input: (12 × 90 × 60) / (80 × 1000) = 0.81 kJ/mm — within the recommended range for a root pass.

Always record actual current, voltage, travel speed, and interpass temperature on the weld log. If the welder deviates, the QA team has data to assess the joint instead of guessing.

6. Post-Weld Treatment and Quality Control

A Cuni weld is not finished when the arc stops. The post-weld sequence below should be in the WPS and on the inspection and test plan (ITP).

6.1 Cleaning and pickling

• Brush the weld with a stainless-steel brush to remove the dark oxide film.
• Pickle with 10% nitric acid solution, then rinse thoroughly with deionised water. Residual acid will attack the joint in service.

6.2 Non-destructive testing

• Visual inspection (VT): 100% of welds, before and after pickling.
• Dye penetrant test (PT): on root and cap surfaces of all butt welds. EEMUA accepts PT as the primary surface method.
• Radiographic test (RT): on a project-defined sample, typically 10-20% of butt welds. RT catches internal porosity and lack of fusion.
• Ultrasonic test (UT): where access for RT is limited or for welds above 6 mm wall. UT is also used to map wall thickness during service.

6.3 Hydrostatic test

Pressure-test the completed system at 1.5 times the design pressure (or as the project specification requires) for at least 30 minutes. Use clean freshwater; chloride-rich seawater in a hydrostatic test can mask leaks and damage the Cuni surface.

6.4 Documentation

• Weld log with heat-input data.
• NDT reports with film or digital records.
• Welder qualification certificates (e.g., EN 9606-4 or ASME Section IX).
• WPS and PQR traceability numbers.

When the welded line is connected to flanged equipment, the bolted joints must be torqued to the WPS value using a calibrated wrench — and the gasket must be the type specified for Cuni service, typically compressed graphite or PTFE. See the pipe fittings and pipe flanges ranges for compatible components.

7. Common Problems and How the Procedure Prevents Them

Three defects show up most often on Cuni welds. Each one is preventable with the right procedure.

7.1 Porosity

Cause: contaminated surface, impure shielding gas, moisture in the filler. Procedure response: enforce cleaning, ｒｅｐｌａｃｅ gas cylinders below 20 bar, store filler dry, and run a porosity test on the procedure qualification plate before production.

7.2 Hot cracking

Cause: high heat input combined with sulphur or phosphorus over the EEMUA limit. Procedure response: cap heat input, verify chemistry on the MTR, and preheat thick sections to 100-150 °C when wall thickness exceeds 8 mm.

7.3 Lack of fusion

Cause: travel speed too high or arc too long. Procedure response: set realistic travel-speed limits, monitor arc length visually, and require a backing gas on every root pass.

8. Quick Procedure Checklist for Site Use

Before the welder strikes the arc, the supervisor should be able to tick every box below. If any box is unchecked, do not start welding.

• Pipe alloy, heat number, and MTR confirmed.
• Filler metal, gas, and electrode all in date and in spec.
• Joint cleaned, oxide removed, fit-up within tolerance.
• WPS and PQR available at the work station.
• Welder qualification valid for the process, material group, and position.
• Backing-gas line set up and flow checked.
• Pyrometer or temperature-indicating crayons available for interpass control.
• Stainless-steel brush and pickling solution on site.

Following this checklist, combined with the procedures above, gives a EEMUA 144/234 weld that will pass NDT on the first attempt and stay leak-free for the design life of the system — whether it is carrying seawater across a ship’s engine room, feedwater through a petrochemical facility, or coolant through a heat-exchanger bundle built from B466 copper-nickel tube.