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Finishing a 304 SS welded assembly

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capntom62

capntom62

Aerospace
Oct 17, 2013
20
We make waste water pumps from welded commercial pipe fittings. Marketing is asking us to make them "prettier". We currently wire brush and passivate the welds. Electropolishing will be very expensive because of the sizes. Ø 8-12" Dia pipe fitting assemblies can weigh over 1,000 lbs and be 4' feet high. Any suggestions?
 
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The surface finish must be the same as the piping.

Regards
 
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I am not sure if you are asking that question or making a statement.
The details of the assembly would prohibit that level of uniformity. Some details are cast, extruded or rolled and welded pipe. They just need to look professionally made to a non technical person.
 
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Assuming the welds are structurally sound, what is marketings's beef? Heat tint? Spatter? Want to post a picture of a "bad looking" weld?

I'd avoid wire brushing, just because the usual steel wire can embed bits of wire into the stainless, and you would then fail a passivation test; hopefully you are using a stainless brush. Using an abrasive flap wheel and/or disc sander would be better. Grit blasting might be another alternative.
 
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Op
Look into glass bead peen or blast.
And optional to buff with portable
Using wheels and red rouge, hopefully I spelled it correctly.
 
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Blast will remove all the scale, buffing while not necessary will make them pretty.
 
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capntom62 said:
Marketing is asking us to make them "prettier". We currently wire brush and passivate the welds
Click to expand...

Perhaps you should ask them for a picture of what it is that “prettier” means or looks like to them. As professionals, we ensure the welds meet the code of construction.

The devil is in the details; she also wears prada.
 
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Here's the deal gentlemen, manufacture parts can be not be pleasant to the eye but functional. And meet all the standards.
But when parts or assemblies are pleasant to look at. A fascinating act happens. Inspectors, and customers are
More pleased with the results.
On the type of work I do. I would have then bead blast after heat treat. To remove oxides and scales.
If temper etch and bake required and no plating I would require a very light bead blast and buff. To make them shiny.
Or a least pleasant to look at.
The customers upon receiving were very happy. Of course all was to specification , dimensional and on.
Just be mindful of close tolerances.
Some operators try to do to good of a job. And close tolerances will go out of spec.
 
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Either blast the whole thing with fine shot or brush finish the whole thing.
High purity piping has a '189' finish just so that it all looks the same.
And passivate after your finishing to remove trace metal that could lead to rust staining.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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Curious if coatings are being considered. A picture of what you want to improve upon would help.
 
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capntom62 said:
I am not sure if you are asking that question or making a statement.
Click to expand...

1) My post does not have the (?) symbol, so it is not a question.
2) The required surface finish must be performed on a sample plate prior to commencing manufacturing, approved by the customer. This sample plate is used for comparison with the production part.

Regards
 
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Train the welders, so that they make more uniform (visualle pleasing) welds?
Use rotating devices, so the welds are made in 1G?
Change weld process (if only for the cap)?

Here's an example of one of our interventions (before/after).
Is it something similar you're looking for?

before-after.jpg
 
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We are leaning towards a portable buffing process. Lots of great responses, and some good questions. "What do they want?" As "mfgenggear" states, non technical people do not know what they are looking at and favor the prettier products. Blasting, electropolishing or coatings cost too much (in their eyes).
 
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OP
Bkasting is a very effective and efficient method of scale removal.
Did you try quoting to farm it out, or
Quote a large blasting cabinate.
Good air pressure is required.
Purchasing abrasive blast. It's very
Economical.
 
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The assemblies can be quite large, 4' foot cube and weigh 2,000 lbs. A cabinet would be large, with cranes or hoists to move parts around, ventilation system constraints, labor hours to blast. We had one blasted in our parking lot months ago and it took about 4 hrs. I have designed and built a few large ones in my aerospace career. Farming it out has cost, delivery issues and lead time. They want a "quick and cheap" solution. I HATE using that phrase, as I am sure we all do. There is no scale. It is 304 SS cast elbows, extruded or rolled / welded pipe and forged flanges.
 
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We had a walk-in blasting room that used.
Sometimes we could fit one part and sometimes thousands.
There is no cheap way to get a uniform appearance.
It will take time and money.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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If you just pay a welder’s helper to wire wheel the welds, I think you will be pleasantly surprised with the results, as well as the scale of economy to do so.

The devil is in the details; she also wears prada.
 
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You need to figure out, do they want pretty welds or do they want the entire part to have a uniform look?
Two very different requirements.
Just remember to chemically passivate after any surface modifications.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
 
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