Pipe and Tubular Welding for Marine Outfitting Applications

Pipe and Tubular Welding for Marine Outfitting Applications

Pipe welding is one of the most demanding skills in marine fabrication. Aboard ships, pipe systems carry fuel, seawater, freshwater, hydraulic fluid, and exhaust. A failed weld can flood a compartment, start a fire, or disable propulsion. For that reason, pipe welds in marine outfitting are held to strict workmanship and testing standards — including visual inspection and mechanical bend testing against codes such as AWS D1.1 and ABS/USCG requirements.

Why Pipe Position Matters

Unlike plate welding, a pipe coupon presents a continuously changing weld angle as you travel around the joint. Two test positions are covered in this lab:

• 2G (horizontal-fixed): The pipe axis is vertical. The weld groove runs horizontally around the pipe. You weld in the horizontal position throughout — the pipe does not rotate.
• 5G (horizontal-fixed, rolled and vertical): The pipe axis is horizontal and the pipe is fixed. As you travel around the joint, you pass through flat (12 o'clock), vertical (3 and 9 o'clock), and overhead (6 o'clock) positions in one continuous weld. This is the most challenging common pipe test position.

Mastering both positions is essential for marine outfitters because pipe is installed in every orientation inside a hull.

Electrode Selection: E6010 Root, E7018 Fill and Cap

E6010 is a cellulosic, fast-freeze electrode that runs on DC electrode-positive (DCEP). Its slag freezes quickly, which lets you maintain a keyhole at the root and achieve full penetration on open-root pipe joints even in vertical and overhead orientations. It produces a thin, easily chipped slag.

E7018 is a low-hydrogen, iron-powder electrode that also runs on DCEP. It produces a smoother, stronger bead with a dense slag and is used for fill and cap passes. Because it is low-hydrogen, E7018 must be stored in a rod oven (typically maintained around 250–300 °F per manufacturer guidance) and used promptly after removal to prevent moisture pickup, which can cause hydrogen-induced cracking.

Never use E7018 for the root pass on an open-root pipe joint — its heavy slag and slower freeze make keyhole control very difficult.

The Keyhole Root Pass Technique

The keyhole is a small, controlled opening that forms at the leading edge of the weld puddle as the root faces melt back. It confirms that fusion is occurring through the full root face thickness. To maintain a keyhole with E6010:

1. Hold a tight arc — approximately equal to the electrode diameter.

2. Use a slight whip-and-pause or steady push technique depending on position.

3. Watch for a consistent oval keyhole about 1/8 inch wide at the front of the puddle.

4. Travel speed and arc length control keyhole size. Too slow = burnthrough; too fast = incomplete penetration.

The instructor will demonstrate this on a 5G coupon before students attempt root passes independently. You must have your root pass visually approved before adding fill passes.

Interpass Temperature Control

Heat accumulates in pipe as weld passes are deposited. If the interpass temperature — the temperature of the base metal just ahead of the weld — is too high, mechanical properties can degrade. For carbon steel pipe with E7018, a maximum interpass temperature of 400 °F (204 °C) is a widely recognized limit in structural welding; always follow the applicable procedure specification (WPS) if one is in use.

Measure interpass temperature with a contact thermometer (also called a contact pyrometer or digital thermocouple probe) on the pipe surface near the joint, not on the weld bead itself. Record every reading in your lab log before beginning each pass. The instructor will sign off your log to verify compliance.

Visual Inspection Criteria

Before bend testing, every coupon must pass visual inspection. Key AWS D1.1 visual acceptance criteria for welds include:

• No cracks of any kind
• Complete fusion along the weld toes and between passes
• No crater cracks at stops and starts
• Undercut no greater than 1/32 inch (shallow and gradual)
• Weld profile must not have excessive convexity or concavity
• No porosity clusters or piping porosity exceeding allowable limits

Use a fillet/profile gauge to check weld reinforcement and profile. Clean the coupon thoroughly by chipping and wire-brushing before inspection.

Guided-Bend Test

The guided-bend test is the standard mechanical qualification test for pipe welds. The coupon is sectioned, the faces are ground smooth, and specimens are bent in a fixture designed to wrap the weld around a specific-diameter plunger (die). Two types of specimens are bent:

• Root bend: Weld root faces outward (tensile stress on the root)
• Face bend: Weld face faces outward (tensile stress on the cap)

Acceptance criterion: No single crack or open discontinuity exceeding 1/8 inch (3 mm) measured in any direction on the convex surface after bending. Cracks at the edges of the specimen that originate in the base metal are typically disregarded.

Photograph both bent specimens and document pass or fail in your lab log with measurements of any indications found.

Safety in the Pipe Welding Lab

• PPE required at all times: welding helmet (appropriate shade lens for amperage used), leather gloves, leather jacket or FR sleeves, leather boots, safety glasses under the helmet.
• Ventilation: SMAW on carbon steel produces iron oxide fume and manganese. Use local exhaust ventilation (LEV) at the weld point. Never weld in a confined space without an air-monitoring and confined-space entry permit.
• Angle grinder safety: Wear a face shield over safety glasses. Inspect grinding wheels before mounting. Secure the pipe firmly before grinding.
• Band saw / pipe cutter safety: Follow the shop's lockout/tagout (LOTO) procedure when changing blades or clearing jams. Keep hands clear of the blade path.
• Hot metal: Freshly welded pipe reaches temperatures that cause instant severe burns. Use tongs or insulated gloves when handling coupons. Mark hot metal with soapstone and call "hot" aloud.
• Rod oven: Do not block or defeat the oven thermostat. E7018 kept out of the oven for extended periods must be re-dried per manufacturer instructions before use.
• Eye protection during chipping: Flying slag can cause serious eye injury. Keep your helmet down or wear safety glasses when chipping near others.