47963

Laser Scoring Stainless Steel [Missouri] 

February 22, 2008

I am a product development engineer for a company that manufactures Rupture Discs. Rupture Discs are a one-time-use pressure relieving safety device used mostly in pressure vessels, pipe systems, and other various fluid environments. The discs are scored (mechanically) such that when the pressure in a system reaches a maximum limit, the disc "ruptures" (hence the name) and the pressure is released. This prevents the explosion of whatever device or vessel was under pressure. The disc opens much like the top of an aluminum beer can would open.
Recently we have started researching the potential of using lasers to score the rupture discs instead of using a blade. The material being scored is 316 and 316L stainless steel sheets, .015" - .05" thickness. The score is generally made to 80-90% of the material thickness. What affect will the laser scoring have on the passivity layer of the steel, and more importantly, the corrosion resistant properties of the stainless steel material? Furthermore, I will have to test and verify the positive or negative affects of the laser scoring; time is a constraint for this project, is there a process to accelerate the corrosion of the samples?
Thank you in advance for any help you can offer.

Greg Snow
product development engineer - Liberty, MO, USA

It can be done, but greed normally causes problems It requires a specific laser and it requires a narrow range of power and feed speed to not cause black slag in the remelt zone. This area is normally high in carbide composition and does not passivate well. You will be making a relatively heavy pass on the 0.050 material which will be more difficult.

James Watts
- FL

YOUR ACTUAL ANALYSIS:
Rupture Discs are a one-time-use pressure relieving safety device used mostly in pressure vessels, pipe systems, and other various fluid environments.

DISCUSSION: MECHANISME (FORCE TEST)
You are talking about a FORCE (physicaly, i.e. P/A) resistance.

YOUR PROPOSED TEST (LASER,i,e, energy)
I don't see the equivalence of the test. At least you find a parameter that respond to it.
Material change will be involved in this test.

MY SUGGESTION
Explain better the idea of such test.

Jose Castellanos
- Minneapolis, MN, USA

The laser will create a heat-affected zone and surface condition that will decrease the corrosion resistance. A comparison of the corrosion resistance can be done quickly using electrochemical corrosion testing methods. This testing will give a threshold for initiation of pitting corrosion, which will allow a direct comparison of mechanical versus laser scoring. The test can be done in a matter of hours versus weeks or months for more traditional corrosion tests.

Larry Hanke materials testing laboratory Minneapolis, Minnesota

LARRY,

You mean measure CORROSION RESISTANCE as a function of the LASER MATERIAL ATTACK. Then correlate such function with the PRESSURE RESISTANCE test?. FInally find the CRITICAL RUPTURE CONDITIONS? Is like this?
Now, make sens for me.
Otheway, do you have articles (references) to read about it?
I am located in Minneapolis too.

Jose Castellanos
- Minneapolis, MN, USA

Repassivation of laser marked areas is almost always required to prevent corrosion there. Usually this comes up with things like the marks on surgical instruments but it will no doubt be the same for you. Even using a blade to make your scores, the area should be passivated afterwards to help prevent corrosion.

Ray Kremer Stellar Solutions, Inc. Algonquin, IL, USA

Greg,
Chem-etch will not disturb the integrity of the material while offering a consistent depth for uniform "bursting". We can selectively chemically etch your stainless material to any specified depth. We have done similar projects for experimental papplications similar to your purpose only for military armaments. Feel free to give us a call.

If there is a concern with corrosion,we can also e-coat clear or translucent colors with UV stable additives. Coating is about 14 microns (.0005").<

Mike Dywan
PMA Photometals, Inc - Phoenix, AZ, USA