Purge paper and preformed purge dams do the same job: they seal the pipe either side of the weld so you purge a small chamber instead of the whole line, then dissolve in water after welding. The difference is how much work goes into each dam. This guide explains when each makes sense, using Aquasol’s water-soluble range as the example.
The short answer
- Use preformed purge dams (Aquasol EZ Purge) for repeat work on standard pipe sizes. Peel, insert and press — no measuring or cutting.
- Use purge paper and tape (Aquasol water-soluble paper) for one-off diameters, ducts, square or irregular openings, and small quantities of an unusual size.
- Use purge film (Aquasol Liquifilm) when you want a custom-cut dam you can see through to check placement.
Side by side
| Preformed purge dams | Purge paper & tape | Purge film | |
|---|---|---|---|
| Product | EZ Purge | ASW paper + ASWT tape | Liquifilm |
| Sizes | 1/2 to 84 in. pipe (1/2–3 in. custom order) | Sheets and rolls up to 31 in. wide; tape 1 and 2 in. | 1 m x 20 m rolls |
| Set-up | Peel, insert and press | Measure, cut, shape and tape | Cut, fold and tape |
| Best for | Repeat standard sizes | One-offs and odd shapes | Custom dams you want to see through |
| Removal | Dissolves in water or steam | Dissolves in water or steam | Dissolves in hot or cold water or steam |
Where preformed purge dams win
Every paper dam has to be measured, cut, assembled and fitted. A preformed dam skips all of that. Aquasol EZ Purge dams have tapered side walls that fit a range of pipe schedules, pre-installed water-soluble tape for alignment, and a ZAP (Zero Air Permeability) construction designed to hold purge gas. On a job with many joints at the same size, the labour saved usually outweighs the higher cost per dam, and set-up is the same for every welder.
Where purge paper wins
Paper and tape handle anything a stock dam can’t: one-off diameters, ducts, square or rectangular sections, reducers, and openings with obstructions. It also makes sense when you only need a few dams at an unusual size and don’t want to stock a full case.
Choosing a paper grade
| Grade | Thickness | Use it for |
|---|---|---|
| ASW-35 | 0.0035 in. | Pipe up to 4 in. inside diameter |
| ASW-40C | 0.0050 in. | Higher purge-gas retention |
| ASW-60 | 0.0070 in. | Pipe 4 in. inside diameter and larger |
| ASWT tape | 1 or 2 in. x 300 ft. | Sealing the paper to the pipe wall |
Making a paper dam
- Clean and dry the inside of the pipe where the dam will sit.
- Cut a disc of paper a little larger than the pipe’s inside diameter, so the edge can fold against the wall.
- Fold the edge into a lip, set the dam in the pipe and seal the lip to the wall all the way round with water-soluble tape.
- Repeat on the other side of the joint, purge, and confirm the oxygen level with a weld purge monitor before welding.
How far from the weld should the dam sit?
Aquasol’s guidance, or the distance your project engineer specifies:
| Pipe size | Distance from the weld joint |
|---|---|
| 2–8 in. (51–203 mm) | 6 in. (152 mm) |
| 10–22 in. (254–559 mm) | 8 in. (203 mm) |
| 24–36 in. (610–914 mm) | 12 in. (305 mm) |
| 40 in. and up | 24 in. (610 mm) |
Water-soluble dams or inflatable bladders?
Water-soluble dams are single-use and need a water or steam flush to remove, but they can go where nothing can be pulled back out — long runs, closed systems, past bends. Inflatable purge bladders are reusable and retrieved after welding, so they pay off on frequent work where the pipe end is accessible.
Frequently asked questions
Is purge paper the same as welding rice paper?
Yes. “Rice paper” and “dam paper” are welders’ names for water-soluble purge paper. Aquasol’s is made from sodium carboxymethyl cellulose and wood pulp, not rice, and dissolves in water.
Which is cheaper, purge paper or preformed purge dams?
Paper costs less per square foot, but every dam has to be measured, cut, assembled and fitted. On repeat work at standard sizes, preformed EZ Purge dams usually save more in labour than they cost.
How is a water-soluble purge dam removed?
Flush the line with water or steam, for example during the hydro-test. The paper, tape or dam dissolves, so nothing has to be retrieved from the pipe.
Can water-soluble dams be reused?
No. They are single-use. For a reusable option, use inflatable purge bladders, which are pulled out after welding.
Which purge paper grade should I use?
ASW-35 for pipe up to 4 in. inside diameter, ASW-60 for 4 in. and larger, and ASW-40C where higher purge-gas retention is needed.
Compare Aquasol water-soluble purge products or request a quote — call 1-866-277-0661.