What's the Point of Running Stringers?

Date 06-19-2007 11:10

ZCat,
Can be a combination of both. One thing most overlook, by many folks, is that the only thing that matters in how quickly you get a joint welded out is the effective deposition rate. Even with SMAW, how much weld metal is deposited (lbs/hr for example) determines how long it takes to fill a joint with given volume. With many materials (like stainless steels) the slower you travel, the more heat buildup there is and that can affect the bead shape, material properties, etc., especially when welding out of position. I understand that you can get better deposition rates with 5/32 than 3/32 or 1/8 electrodes, but on a 96" diameter pipe, I would think that 1/8 and even 5/32 electrodes could be used for most of the fill/cap passes.

On the higher strength pipe materials (API 5L, X65 and up) heat input can greatly determine the final weld mechanical properties (including HAZ). Most higher quality piping weld codes will place some limit on bead width.

Just another way to look at this subject.

By dbigkahunna (****)

Date 06-19-2007 12:53

Heat input is directly related to bead width. The smaller the bead, the less heat input because HI is time and speed. On structural,and tanks this is usually not an issue (fertilizer tanks are an exception). On pipe it can be critical. Especially if the material will be exposed to high temp, hydrogen or H2S.

By js55

Date 06-19-2007 13:33

Actually, higher heat input that will increase grain size is generally beneficial to high temperature applications involving ferritic, bainitic, and martensitic materials. Small grain size is beneficial for lower temp applications where toughness is an issue. In regimes where creep is an issue larger grains inhibit creep. In fact, every material has a specific temperature of service in which the strength benefits of large grain and small grain transition. Off hand I forget the name of this transition temperature (gettin old I suppose) but it is related to creep service.
But as with all things, there is a limit. And this will generally be related to elements being precipitated out of solution, or carbide precipitation and such, and reducing the strength of the material, or for even that matter issues of cold temp transport and start up dynamics, etc. Once again, there is no replacing well considered engineering with cookbook methods.
Also, even austenitics see benefit from larger grain sizes in creep regimes, if this were the only phenomena of import. But with austenitics hot crack phenomena and segregation of corrosion resisting elements will take precedent, limiting to a greater extent the heat input this material type can tolerate.

By Rparz Date 06-19-2007 22:52 Edited 06-19-2007 22:57

[quote]

Actually, higher heat input that will increase grain size is generally beneficial to high temperature applications involving ferritic, bainitic, and martensitic materials. Small grain size is beneficial for lower temp applications where toughness is an issue. In regimes where creep is an issue larger grains inhibit creep. In fact, every material has a specific temperature of service in which the strength benefits of large grain and small grain transition. Off hand I forget the name of this transition temperature (gettin old I suppose) but it is related to creep service.
But as with all things, there is a limit. And this will generally be related to elements being precipitated out of solution, or carbide precipitation and such, and reducing the strength of the material, or for even that matter issues of cold temp transport and start up dynamics, etc. Once again, there is no replacing well considered engineering with cookbook methods.
Also, even austenitics see benefit from larger grain sizes in creep regimes, if this were the only phenomena of import. But with austenitics hot crack phenomena and segregation of corrosion resisting elements will take precedent, limiting to a greater extent the heat input this material type can tolerate.

[/quote]

Dumb question -- Where did you learn this much detail about welding? Are you an Engineer? Could you recommend some books for further reading? Thanks.

By js55

Date 06-20-2007 13:37

Rparz,
There are a lot of great books out there. Linnerts Welding Metallurgy was one of my first. The ASM (especially Volumes 4, 6, 8, and 10) and AWS Handbook series'. IIW has a tremendous library of tech articles(free). Lincoln, Miller, Alcotec, and Nidi, have terrific websites with articles(free). ESAB has some very good Handbooks. The Welding Journal Research supplement. TWI, WRC, the Department of Energy, Woodhead Publishing are other great resources. ASTM has some great technical publications. And once you start collecting these they will of course reference others and the snowball grows. Before too long your wife is complaining about why you haul this tonnage around with you wherever you go.
But to be honest, the greatest resource of information that I've been exposed to is people. People in AWS, ASME, ASNT, EPRI, TPA, etc. There are a lot of great people out there that are more than willing to share their knowledge (like many in here) with others who demonstrate a desire to apply themselves.

By Mwccwi

Date 06-20-2007 23:07

A not so expensive yet highly informitive starter choice would be Lincoln Electric- 2 books both less that $30.00 Metals and how to weld them, and Welding Procedure Handbook

By darren

Date 06-19-2007 23:02

could you please explain "creep" to me.
thanks
darren

By ZCat

Date 06-19-2007 23:27

This is definitely gonna be a high temp application, not sure what the working temp is, but we are welding on the tube headers at the moment. It's just A36 pipe using 7018, so nothing exotic.
I know up in Alaska they were very concerned with heat input and charpies and bead width and kilojoules and all that mumbo jumbo. We used a lot of x65 pipe and it was cold temps outside. I think it's going to be plenty warm where this pipe is gonna be.

By js55

Date 06-20-2007 13:55

I would think that for tube headers creep would be a greater material property concern than toughness. Even for Alaskan applications. Although, given the extreme ambient conditions I would suspect some accomodation for toughness due to cold during start up, shutdowns, and transport. However, the stress level imposed on the material is not one of service.
Some power alloys have ductile to brittle transitions well above lower 48 ambient conditions (especially North Dakota, Minnesota, or as jon can testify, Michigan) and therfore there is concern there as well for some toughness.

By js55

Date 06-20-2007 13:45

darren,
To put it crudely creep would be a long term deformation of material that takes place, generally in high temp regimes, wherein the material essentially pulls itself apart under stress, creating voids. I suppose there are better and more accurate or sophisticated definitions, and you can probably find them on the web or in tech books and articles. But this captures it informally for me.
The advantage to large grains in creep resistance is that they resist the sliding of grains against each other. Much like the difference between sliding two pieces of sandpaper as opposed to two pieces of glass.
I spent some time in a power shop where creep regimes are a very consistent concern.

By darren

Date 06-20-2007 17:52

deformation in hydraulics from heat and pressure. ahhh
works for me and i dont think it is a crude definition.
conversely some of the engineering defs although more concise leave a guys head reeling. i know stephan sent a transfer mode article for fcaw that was very informative and there were about twenty types of transfer with either the discovering engineers name or some other intuitive name, although i had seen or used most of the modes of transfer (i just put up with the way the machine was set for a lot of them instead of setting the machine that way on purpose) the statistical and engineering descriptions were way less useful to my understanding than the pictures and simple down on the floor terms. after all if we cant find a term that we are comfortable with that explains something to us, all the big words and study doesn't help the job get done. i think that the engineers have a tougher time with reverse understanding. taking an actual event, something we are already doing because experience has proven that it is the best way to do a task and then developing the scientific model and going about the daunting task of figuring out what the hell just happened and why we should keep doing it that way. (the diffusion of hydrogen thread on this forum comes to mind) some of the best tradesmen i know have no idea what is happening on a scientific level they just know from experience the way that works. some of the most ingenious solutions have come from people that didn't have someone around telling them that they are 'too stupid' or that 'their ideas would never work'. some of the solutions to problems on some farms have more ingenuity than that almost 40 year old tin can we keep blasting into space (space shuttle)
thanks for the definition
darren