INTRODUCTION TO WELDING

PROCESSES FOR REFRIGERANT

PIPING AND VESSELS

Douglas Reindl, Ph.D., P.E.

Professor & Director

University of Wisconsin-Madison

Industrial Refrigeration Consortium

Welding basics

• Joining of two or more materials by

coalescence

• Most processes involve significant heat addition

• Shielding – protection of the weld puddle

• Essential to prevent unwanted reactions (oxidation) between

weld puddle and ambient

• Provided by vaporizing a flux or externally supplied gas

• Must remain present until puddle solidifies

Welding Processes - SMAW

• Shielded Metal Arc Welding (stick)

• Uses a consumable flux-coated electrode

• Typically DC current, electrode is positive

• Shielding gas is created by melting flux

• Widely used in pipe fabrication (carbon steel)

Excerpted from Welding tips and tricks

Excerpted from Welding tips and tricks

SMAW

• Advantages

• Versatile welding process

• No external shielding gas

required

• Moderate production rates

• Low equipment cost

• Allows welding in any

position

• Disadvantages

• Dirty process

• Susceptible to slag

inclusion in weld

• Relatively slow production

process

• Frequent starts and stops

• High filler material waste (electrode stubs)

Welding Processes – GTAW

• Gas Tungsten Arc Welding (TIG)

• Non-consumable tungsten electrode to sustain arc (DCEN)

• Welds with and without filler (filler fed by hand)

• Separately supplied shielding gas (Ar, He, and mixes)

• Produces a clean weld

• In refrigerant piping, it can be used for root pass

Excerpted from Welding tips and tricks

GTAW – example of electrode selection

GTAW

• Advantages

• Welds more metals and

metal alloys than any

other process

• High quality and

precision

• Minimal HAZ

• Aesthetic welds

• No sparks or spatter

• No flux or slag

• Disadvantages

• Cannot weld

uncontrolled ambient

conditions

• Requires backing gas if

internal cleanliness is

required

• Low production rates

due to slow process

• Generally requires

higher operator skill

Welding Processes – GMAW & FCAW

• Gas Metal Arc Welding (MIG) / Flux Cored Arc Welding

• Wire-fed electrode creates arc in a short-circuit to metal [MIG] (polarity is important - DCEP for solid wire & DCEN for hollow core wire)

• Hollow wire-fed electrode filled with flux [FCAW]

• Separately supplied shielding gas (CO2 and mixes) [GMAW]

• Commonly used in production shops (e.g. metal fab, structural,

pressure vessels [FCAW])

GMAW

• Advantages

• Hi production rate

• Less spatter than SMAW

• No flux or slag (FCAW will

have slag)

• One of the easiest

processes to learn

• Can be used in all

positions

• Disadvantages

• Cannot weld

uncontrolled ambient

conditions

• More difficult in using for

out of position welding

GMAW

Source: Lincoln Electric

Excerpted from Welding tips and tricks

Welding Processes – SAW

• Submerged Arc Welding

• Wire-fed electrode creates arc in a short-circuit to metal

• Granular flux applied over arc creates shielding gas

• Typically limited to flat position fillet and groove welds

• Commonly used in production shops (e.g. pressure vessels)

SAW being used for vessel fabrication

SAW – horizontal position only

Operator console

Display showing depositing of granular

flux ahead of the continuous fed electrode

Product of SAW pass

SAW

• Advantages

• Hi production rate

• Capable of very high

amperage

• Can accommodate

welding thick sections

• High quality welds with

minimum operator skill

• Disadvantages

• Can only be used in flat or

horizontal positions only

• Practical only in a shop

environment

• Weld pool itself is under

pool of granular flux

Filler materials

• General care and handling

• Moisture is a big enemy

• Keep them clean and dry!

• Avoid contact with grease, oil, and debris

• E7018 must be kept in a rod oven or hot box to

avoid weld porosity

SMAW Electrodes – AWS A5.1

SMAW Electrodes

• Two common electrodes used

for pipe are E6010 & E7018

• E6010

• Typically used for root pass

• Cellulose-based coating

• E7018

• Typically used for fill and cover passes

• Low hydrogen rod

• Kept in a rod oven to avoid moisture infiltrating the rod

coating which can lead to weld porosity

Source: Lincoln Electric

GTAW electrodes – AWS5.18

• Carbon steel to carbon steel

• ER70S-3

• Carbon steel to stainless steel

• ER309 or ER309L filler

• Generally pick filler yield strength

to match the higher strength mtl.

E R X X S - X

Electrode

Min tensile

strength ksi

Solid wire

Chemical

composition

LET’S TEST YOUR

KNOWLEDGE!

The following questions are intended to apply to the fabrication of

refrigerant piping for industrial ammonia refrigeration systems.

Test your welding IQ

1. It is permissible to commence pipe welding

with metal temperatures at or below 32F.

True or False?

Q #1 is False

527.3.1 General. No welding shall be done if the

weld area is wet or exposed to high wind or at a

metal temperature below 32°F (0°C).

Test your welding IQ

2. It is permissible for an apprentice to tack

sections of pipe together as long as a

certified welder performs the root pass.

True or False?

Q #2 is False

527.3.2 (b) Tack welds shall be made by a

qualified welder or shall be removed. Tack

welds that are not removed shall be made with a

filler metal that is the same or equivalent to the

electrode to be used for the first pass. Tack welds

that have cracked shall be removed. …

Test your welding IQ

3. The use of backing rings for pipe is not required but when used, the backing rings can be either ferrous (metallic) or nonferrous/nonmetallic.

True or False?

Q #3 is True

527.1.2 The use of backing rings is not mandatory

but; however, when used, they shall conform to the

following requirements

a. Ferrous rings shall be made from material of

good weldable quality, and the sulfur content

shall not exceed 0.05%. Preferable material is

same chemical composition as the parts being

joined.

b. Backing rings made of nonferrous or nonmetallic

materials may be used provided they have no

effect on the weld or the contained fluid.

Satisfactory use shall be demonstrated by

qualification of the weld procedure.

Test your welding IQ

4. The code requires that socket welds have

the pipe fully inserted to the base of the

receiving socket before welding.

True or False?

Q #4 is False

Test your welding IQ

5. The required examination for welds in

accordance with ASME B31.5 is visual.

True or False?

Q #5 is True

536.4.1 Visual Examination Prior to operation, visual examination is required in accordance with this paragraph for all refrigerant and secondary coolant piping.

Visual examination is the observation of whatever portions of components, joints, and other piping elements that are exposed to such observation either before, during, or after manufacture, fabrication, assembly, erection, inspection, or testing. This examination may include verification of the applicable requirements for materials, components, dimensions, joint preparation, alignment, welding or joining, mechanical joints, supports, assembly, and erection.

Test your welding IQ

6. Seal welding of threaded joints is

permitted as long as the external threads

are completely covered by the weld.

True or False?

Q #6 is True

527.3.1 Seal Welds. Where seal welding of

threaded joints is performed, external threads shall

be entirely covered by the seal weld. Seal welding

shall be done by qualified welders.

How did you do?