Intermittent fillet welds & corrosion 1

[STpipe]

Hey everyone,

I'm looking for guidance on checking/specifying an intermittent fillet weld design based on the Eurocode from people far more familiar with it than I am.

Looking at EN 1993-1-8, clause 4.3.2.2, I noticed the first provision states "1. Intermittent fillet welds should not be used in corrosive conditions."

As I'm more familiar with the American steel code, I found that particular clause interesting because there is no indication of this requirement in AISC 360. My questions would be:

1. How much of a hard requirement is this? I notice the clause states "should" rather than the more authoritative "shall", which implies it's more of a recommendation.
2. What would be the definition of "corrosion conditions". Would it be when directly exposed to the corrosive elements, perhaps like in offshore situations or directly exposed to corrosive liquids, or could it even be for an outdoor environment on the coast?
3. Why is this a requirement that's found in the Eurocode, but absent from AISC?

Thanks.

 

[GeorgeTheCivilEngineer]

1. Generally 'should' in Eurocodes needs to be adhered to unless you can propose an alternative solution which satisfies the principle clause (if present) or achieved the same effect. In this case increasing the protection provided by the paint/galvanizing would achieve that.
2. I've always used SCI corrosive categories which means C3/C4 or above is likely to apply to this requirement. Long term access and structural importance could play a role.
3. No idea

 

[r13]

3. Suggest to check AWS D1.1

 

[FLCraneBuilder]

Corrosive conditions cause me to spec either continuous welds
or
polyurethane caulk After first coat of protective coating, and prior to second coat

we are design-build, so this is often presented as an option to owner... its like an insurance policy - pay me no or pay me a lot more later

if hot-dip-galvanized, then the acid will eat into the gap between lies & cause problems quickly

 

[STpipe]

Hey everyone,

Wanted to revive this topic as I got flooded with the holidays and didn't get around to responding. Many thanks to all of you for taking the time to respond.

1. Generally 'should' in Eurocodes needs to be adhered to unless you can propose an alternative solution which satisfies the principle clause (if present) or achieved the same effect. In this case increasing the protection provided by the paint/galvanizing would achieve that.
2. I've always used SCI corrosive categories which means C3/C4 or above is likely to apply to this requirement. Long term access and structural importance could play a role.
3. No idea

Thanks for the clarification on the language in the Eurocodes. I'll definitely keep that in mind in the future. So as long as appropriate corrosion protection is provided, I can still satisfy this particular clause while still using intermittent welds.

3. Suggest to check AWS D1.1

Any specific section you have in mind? I took a quick browse through the document, and the best that I could find are references to mastic and nonmetallic fillers which implies the need for sealing and corrosion protection which is in line with what FLCraneBuilder recommended in his post.

Corrosive conditions cause me to spec either continuous welds
or
polyurethane caulk After first coat of protective coating, and prior to second coat

we are design-build, so this is often presented as an option to owner... its like an insurance policy - pay me no or pay me a lot more later

if hot-dip-galvanized, then the acid will eat into the gap between lies & cause problems quickly

Thank you for this information, I'll definitely keep that option in mind.

 

[r13]

STpipe,

I shall have said "contact AWS", instead of "check AWS". But here is an explanation on the preference of continuous weld over intermittent weld in a corrosive environment.

... Also, the portions of a weld joint that are left unwelded could be in the form of a crevice. This crevice may accumulate foreign material that could increase the corrosion rate of the base material.

Is this the stance the Eurocode is taking?

 

[BMart006]

Regardless of code requirements, not using intermittent welds in corrosive environments is a good design principle. Couple reasons:
1. Rusting causes expansion of the material. When rusting is inside a joint (such as internal to intermittent welds) there is a significant pressure created by the intended expansion of the material. I believe the change in volume is several times that of unrusted steel when not confined.
2. All of that internal corrosion is happening in an area you cannot inspect (e.g. corrosion at root of weld).

I would make sure you use continuous welds if possible. If not, seal the joint as FLCraneBuilder suggested or design the joint with enough of a gap that allows water to pass through and not be trapped (room to adequately dry, and hopefully room to inspect).

 

[STpipe]

STpipe,

I shall have said "contact AWS", instead of "check AWS". But here is an explanation on the preference of continuous weld over intermittent weld in a corrosive environment.

Quote (Corrosionpedia)
... Also, the portions of a weld joint that are left unwelded could be in the form of a crevice. This crevice may accumulate foreign material that could increase the corrosion rate of the base material.

Is this the stance the Eurocode is taking?

That is good advice. I'll try contacting them to see what they have to say about it. At the very least, they'll be able to point me in the direction of relevant literature that I can look into. I'm not sure if that's the reason the Eurocode has this provision, but it certainly makes sense that it would be the justification for this clause in the code. One of the frustrating things about the Eurocode is the lack of commentary compared to typical North American codes which provides insight and background on the reasoning behind specific provisions while also providing reference literature you can look into if you need to get additional information that the commentary might not cover.

Regardless of code requirements, not using intermittent welds in corrosive environments is a good design principle. Couple reasons:
1. Rusting causes expansion of the material. When rusting is inside a joint (such as internal to intermittent welds) there is a significant pressure created by the intended expansion of the material. I believe the change in volume is several times that of unrusted steel when not confined.
2. All of that internal corrosion is happening in an area you cannot inspect (e.g. corrosion at root of weld).

I would make sure you use continuous welds if possible. If not, seal the joint as FLCraneBuilder suggested or design the joint with enough of a gap that allows water to pass through and not be trapped (room to adequately dry, and hopefully room to inspect).

Solid post and something I'll definitely keep in mind. The detail that I was looking at before the holidays is a typical field weld detail that senior engineers that work for my company have been using for a long time, with no issues (that I know of). However, this is something that I will need to bring up.

 

[Settingsun]

What are you hoping to find? The intent is to seal the joint. No oxygen means no corrosion. Open crevice runs the risk of corrosion within the joint, in addition to corrosion of the opposite exposed surface (if the crevice is along the thin direction of the steel).

What is the application of your existing detail? Perhaps the environment isn't corrosive if there hasn't been a problem.