Weld purging with water-soluble paper saves shops money.

By Leslie Gordon, associate editor

Once the operator has folded 90° lips in the circles cut out of water-soluble paper, he inserts the dam into each pipe with the lips toward the weld.

For pipes less than 4 in. in diameter, the operator pushes a wad of paper several inches down into each section to be joined.

For pipes greater than 4 in. in diameter, he cuts the paper into a circle with a diameter a few inches larger than the pipe I.D.

The operator traces or impresses the pipe inner diameter on the paper and folds on this line to form a 90° lip. He then inserts the dam into the pipe with the lip towards the weld prep.

The operator peels the tape from its backing and tapes the dam in place.

Dissolvo reports its water-soluble paper makes for efficient, low-cost purge dams in GTAW or TIG pipe and tube-welding applications.

Dissolvo's starter kit contains sheets of the company's water-soluble paper, a roll of adhesive-backed tape used to secure the paper during use, and detailed instructions.

Shops face several options in selecting a purge dam material that best handles their GTAW or TIG pipe and tube-welding applications. One simple technology, which has been around for years, is water-soluble paper. This technology doesn't harm the environment, is easy-to-use, and saves shops money.

Weld purging is used in welding stainless steel and other high-value alloy pipes and tubes in applications involving nuclear power plants, fabrication jobs, chemical plants, paper mills, and pipelines. In this process, an inert gas, typically argon, removes, or purges, the air (oxygen) around the weld area. This ensures high-quality welds and guards against defects such as discoloration, brittleness, and cracking.

To avoid excessive gas use, an efficient purging process involves the operator first blocking a small area inside the pipes containing the weld joint. He does this with mechanical devices or membranes called purge dams. The inert gas is then pumped into the blocked-off area through a hypodermic tube inserted through the weld joint.

Pumped throughout the welding process, the gas maintains a positive pressure, pushing the oxygen out through a small hole in the purge dam. After the operator finishes welding, he removes the dam.

Neil Marshall, general manager of Dissolvo LLC, Croydon, Pa., explains with the company's water-soluble paper, weld purging is a straightforward process. For pipes with diameters less than 4 in., the operator makes purge dams by simply pushing small wads of the paper into the end of each pipe to be joined.

For larger pipes, the operator cuts out circles having a diameter a few inches larger than the pipe I.D. (For example, with a 6-in. diameter pipe, the operator would cut two 8-in.-diameter paper circles.)

The operator lightly presses each paper circle onto a pipe end to make a circular impression on the paper. He then folds along this line to form a 90° lip, creating the paper dam.

He inserts a dam into each pipe with the lips towards the weld, using Dissolvo tape to hold the dams in place. (For pipes larger than 28-in. in diameter, the operator splices together two or more sheets of paper with the tape.)

Controlling pressure inside the dammed area, necessary for a good weld, is also an easy matter. The operator merely punches a small hole or holes in the paper with a handy object such as a pencil. Or he can just leave a slight gap between the two pipe ends.

After welding is completed, flushing the pipe with water dissolves the paper away. Flushing is typically done when the pipes are tested for weld integrity.

Inefficient purging processes
Marshall explains other purging technologies are inefficient compared to purging with water-soluble paper. "For instance, welders tape wooden or plastic discs to the pipe ends, or stuff in foam plugs. Or operators insert pieces of cardboard. Besides being hard to remove or dispose of, these methods do not keep the weld area oxygen-free. Air or moisture can still contaminate the weld area, causing porosity, coking, and oxidation."

He continues, "Some facilities use mechanical bladders. These comprise two 'balloons' fastened to the end of a 'stick,' in turn attached to an inflating device. An operator pushes the stick into the pipe and inflates the balloons, sealing the pipe. After finishing the weld, the operator deflates the balloons and pulls the device out of the pipes. But it's hard to get the bladder out, and operators don't always have a convenient way to dispose of the device."

A few operations use plastic, which Marshall notes is also bad practice. "The plastic is a synthetic polymer derived from petroleum that contaminates the water after dissolving."

In addition, plastic films are moisture sensitive, so welders find them hard to use outdoors, except in extremely dry weather. The films are flimsy and difficult to handle and the liquid adhesive used to attach the film messy to use in the field. Finally, the plastic does not store well. Once a shop opens a package, it needs to immediately use all the material.

Weld purging with water-soluble paper
In contrast, Marshall reports water-soluble paper provides the most efficient, lowest-cost process — and it doesn't harm the environment. Also, the technology has been proven over time. In the 1960s, Gilbreth, Dissolvo's parent company, had already developed the paper and was looking for potential applications. Scientists at Gilbreth patented the technique of weld purging with soluble paper in the early 1970s.

Marshall says infrared spectrometry tests showing the residue from plastic is negligible are misleading. "If you take a small amount of film and put it in a large amount of water, of course the residue is negligible. However, it's still an inorganic material, a contaminant getting into the water system.

On the other hand, the paper is an all-natural material made up of tiny natural wood fibers held together with a cellulose binder. Take a small piece of the paper and put it in a glass of water, then shake the glass. You'll see the paper completely disappear."

Marshall continues, "Dissolvo has a 30-yr history of providing quality products. Using an inferior material can create a large liability, so typically welding crews and contractors don't like to take a lot of risks with purging materials. In another application, Dissolvo paper is used extensively in the food-service industry for labeling on food containers in restaurants and hospitals where it is washed off the containers in dishwashers. If the paper left sludge, it would clog up dishwasher filters, and it would never be used in this application."

He also explains that the paper cost is the lowest material cost in the purge welding process. The price of argon gas has recently gone up. Delivery costs for gas have jumped because of bigger fuel costs. Welding rod and wire prices have also shot up. But the price of water-soluble paper has stayed the same over the last few years. The paper lets companies use expensive materials more efficiently, also saving them money.

Marshall says, "Thousands of welding distributors and all the major sup-pliers of the gases used in weld purging have purchased the paper throughout the years. Dissolvo ships to any location, including jobsites, and is a member of GAWDA and a sustaining member of the AWS."

For more information, contact Neil Marshall, general manager, Dissolvo LLC, Croydon, Pa. Phone (215) 826-2466; e-mail marshall@Dissolvo.com; web, dissolvo.com