welding symbols

By Lawrence (*****)

Date 05-12-2012 16:08

I think your understanding is accurate.

But keep in mind that in the Aerospace/D17 world; that oversized welds, especially fillets can cause negative issues with flow of exhaust/compressor gasses etc. So if you are being gigged for oversized fillets, there may be a reason.

The code may not stipulate, but the class 1 OEM doccument that your inspectors are using might have clearences that the manufacturing/repair welder may not have access to.

So both you and the inspectors may be right... You with your understanding of code, the inspector with their understanding of the specific needs of the assembly/repair.

I would suggest a respectful inquiry with inspection to get some insight into why they think the welds are oversized and to help provide you with guideance to making the best welds possible...

It may be obvious to you (as a craftsman) that when the symbol says fillet weld 1/8" that while the weld cannot be less than one eighth that it's almost impossible to make manual welds exactly perfect, so the craftsman errors on the side of large.... Sooooooooooo..... We need to ask; "How big is too big"????

By welderbrent (*****)

Date 05-12-2012 16:44

Lawrence made a very good response but let me hit this from another direction.

First, I am going to use D1.1 as that is what I am most familiar with and have in front of me, along with A2.4. I don't have or work to D17.1.

Now, I don't think you will find what you are looking for in A2.4. That shows how to draw and interpret weld and welding symbols but not how to apply them as to size of finished welds.

D1.1 Section 5.13 'Conformance With Design' states that the sizes and lengths will be "no less than those specified by design". I'll bet other codes have this provision somewhere as well.

Next, you should probably check your applicable code out as far as the 'Inspection Requirements'. For D1.1 this is Section 6 and especially Table 6.1. There we find that welds have criteria for being undersized. How much undersize, what length of the weld can be undersize, etc.

So, a weld can be undersize within certain requirements. Again, other codes probably have this provision somewhere within their inspection requirements as well.

I believe this is the answer you are looking for in regards to the OP. Welds are indeed to be 'at least' the size indicated in the design documents, within certain perameters anyway.

Now, to look at it from the direction Lawrence came, how about oversized welds. That is not specified in MOST codes as has been discussed on here many times. BUT, there are factors to be considered. Mostly time/cost factors. But also things like other parts that will not fit right if the weld from a previous part is in the way. Also HAZ and other metallugical considerations. Then there is the question of how added materials effect the stresses in the member.

So, we find the weld size is correctly interpreted as being the called out dimension at a minimum. We find there are allowances varying with the applicable code as to undersize tolerances. We find limits to when, where, why and how a weld is allowed to be oversized even without code specifics.

But to really help you find an answer we may need just a little more info. Like, is the discussion around going under or over the called out dimension? And, though you referenced D17.1, what code are you specifically working to and asking about?

Have a Great Day, Brent

By 803056

Date 05-13-2012 18:12

AWS A2.4 is not a workmanship standard. It does not address issues relating to workmanship. For instance, in the case of intermittent filler welds: Does the welder start his layout at the middle of the joint length and work toward the free ends or should the welds be laid out starting at one end and progress toward the opposite end?

Those are workmanship issues not addressed by AWS A2.4.

Continuing with the same example, does the welder have to deposit the weld so that the joint is welded to the very end or is it permitted to begin the first weld several inches from the joint end? Again, that is a workmanship issue not addressed by A2.4.

Workmanship is addressed by the welding standard or the code to a limited extent. The issues addressed are the minimum requirements that must be met. If and when the criteria provided do not meet with the employers (or customer's) needs or expectation, additional criteria can be imposed by the contractor via internal quality control documents or work instructions or by the client via the project specifications.

Fair is fair, the welders and the inspectors should be of equal footing when it comes to knowing what the ground rules are. There should be no hidden agenda where the "acceptance" criteria are suddenly sprung on the welder after the project is underway. Workmanship requirements should be clearly stated and presented to all interested parties before work begins. Most welders do not have access to welding standards or codes, so a management system that doesn't provide their workers with adequate direction is going to suffer the consequences by increased repairs, higher labor costs, customer and worker discontent. A good management system has an established (written) workmanship standard that is known and understood by parties. When a customer imposes additional requirements or requirements that differ from the norm, it is incumbent on the employer to make those alternate requirements known.

As I’ve said before, there are good welders, poor welders, good inspectors and bad inspectors, good engineers and bad engineers. The same holds true for management. Some employers know what they are doing and some, well let’s face it, the lousy employers, like lousy welders, inspectors, or engineers, are usually weeded out and eliminated when times are tough. Darwin works in nature and it works in the in business world.

Best regards - Al

By CWI555

Date 05-14-2012 00:29

My personal experience with aerospace tells me D17.1 is not going to be the end all document for you. Your correct insofar as you have written, but there will be more to it.

Aerospace welds are not d1.1 welds. Consider this; a compressor fan turning at 15,000 rpm. What happens to your car wheel if you are out of balance?
In terms of a car:
60 miles per hour = one mile per minute = 5,280 feet per minute linear velocity.
Wheel circumference in feet = diameter times pi = 27inches/12 inches per foot times 3.1416 = 7.068 feet wheel circumference.
RPM = 5,280 feet per minute traveled divided by 7.068 feet per revolution = 747 RPM
Thats going to be roughly 213G on the OD of the tire.

How much is that? 9.80665 newtons of force per kilogram of mass x 213 = ~ 2088 per kilogram of mass. If you had a weight on the surface of the tire that weighed 1 kilo thats the force you would be dealing with.

Now imagine that on a 48" diameter wheel turning at 15,000 plus rpm. It would not take much of that to catastrophically unbalance the compressor fan.

Then there is the balance and stress delivery problems.

If their busting your chops for oversized welds, you may want to consider why it would matter.

By 803056

Date 05-14-2012 01:26

One reason why compressor fan blades aren't welded.

Al

By Lawrence (*****)

Date 05-14-2012 03:24

Blades get welded every day Al... Even single crystal blades.

By 803056

Date 05-14-2012 03:38 Edited 05-15-2012 13:33

When I mispoke I think along the lines (see the previous post) of blades being welded to the disk, but now that you mentioned it, I recollect the blades being refurbished by welding. I stand corrected in that regard. I still don't recall seeing the rotating blades being welded to the hubs.

Duh, open foot insert foot, bite down hard! Lucky I have my wife's old crutches!

Best regards - Al