Another Hydrogen Bakeout Questions ASME Sect 1 work
Another Hydrogen Bakeout Questions ASME Sect 1 work
(OP)
Regarding common steels such as ASME P1-P5 materials, as I understand it the intent of performing a hydrogen bakeout is to dry out the weld.
The process is primarily performed on welds using the SMAW weld process is it not?
The bakeout is of less importance using weld processes using the GTAW method exclusively is it not?
To ASME, some welds require PWHT and some do not. In varous procedures, I see a trend towards hydrogen bakeout and PWHT being used in the same sentence as if to imply that if a weld did not require PWHT that the same weld would not require a bakeout.
This does not make sense and believe this to be an inaccurate statement. I see the hydrogen bakeout and PWHT as being two entirely different things.
I am currently reviewing a spec for a contractor that has to weld qty 26- 8" 2.25cr elbows inside an HRSG. Half of those require PWHT (sch 120) and half of those do not (sch 100). The weld joints subject to PWHT are (to procedure) are going to go thru a bakeout process at some point after welding and prior to stress relieving. Those weld joints that are not subject to PWHT will not go thru a bakeout at all.
It seems to me that you either do the bakeout promptly after welding or you don't do it at all. What is relevant for sch 100 pipe should be just as relevant (or irrelevant) to perform on a sch 120 pipe. As an owners rep, I am having trouble buying into this.
Using good rod (Lincoln H4) and have adequate electrode drying controls at least documented.
Questions:
How important is the bakeout on 1.25 cr materials (or P1,P5a for that matter) for welds that will NOT be PWHT'd and/or will surely have a delayed PWHT?
What is the point of doing a delayed bakeout? I see none here whatsoever.
How would you perform a bakeout if you did not have electrical resistance heating equipment available? Cant see a guy sitting on top of these welds with a weed burner for two hrs but maybe so?
The process is primarily performed on welds using the SMAW weld process is it not?
The bakeout is of less importance using weld processes using the GTAW method exclusively is it not?
To ASME, some welds require PWHT and some do not. In varous procedures, I see a trend towards hydrogen bakeout and PWHT being used in the same sentence as if to imply that if a weld did not require PWHT that the same weld would not require a bakeout.
This does not make sense and believe this to be an inaccurate statement. I see the hydrogen bakeout and PWHT as being two entirely different things.
I am currently reviewing a spec for a contractor that has to weld qty 26- 8" 2.25cr elbows inside an HRSG. Half of those require PWHT (sch 120) and half of those do not (sch 100). The weld joints subject to PWHT are (to procedure) are going to go thru a bakeout process at some point after welding and prior to stress relieving. Those weld joints that are not subject to PWHT will not go thru a bakeout at all.
It seems to me that you either do the bakeout promptly after welding or you don't do it at all. What is relevant for sch 100 pipe should be just as relevant (or irrelevant) to perform on a sch 120 pipe. As an owners rep, I am having trouble buying into this.
Using good rod (Lincoln H4) and have adequate electrode drying controls at least documented.
Questions:
How important is the bakeout on 1.25 cr materials (or P1,P5a for that matter) for welds that will NOT be PWHT'd and/or will surely have a delayed PWHT?
What is the point of doing a delayed bakeout? I see none here whatsoever.
How would you perform a bakeout if you did not have electrical resistance heating equipment available? Cant see a guy sitting on top of these welds with a weed burner for two hrs but maybe so?





RE: Another Hydrogen Bakeout Questions ASME Sect 1 work
In general for piping, a dehydrogenation heat treatment is not needed when using low hydrogen welding processes for the low alloy steels in question; however, when welding heavy walls where cooling is rapid (essentially quenching to the preheat temp) with resultant martensite formation together with high residual welding stress, it is advisable to provide an intermediate heat treatment (dehydrogenation as a minimum) to prevent delayed cracking.
RE: Another Hydrogen Bakeout Questions ASME Sect 1 work
Agree with the response from stanweld.
Not important IF low hydrogen electrodes are used and properly stored for use, and for joint thickness 2" or less.
If you don't follow the previous response (low hydrogen and thickness).
The bake out would/should not be performed using conventional torch heating.
RE: Another Hydrogen Bakeout Questions ASME Sect 1 work
"If you don't have time to do the job right the first time, when are you going to find time to repair it?"
RE: Another Hydrogen Bakeout Questions ASME Sect 1 work
As stated in AWS D10.10 hydrogen bake out is performed to remove hydrogen from material prior to manufacture, fabrication or repair activity. So the process is used not only after welding or repair welding but also in some cases before welding when the base metal contains hydrogen due to service exposure and intents to avoid hydrogen cracking after completion of the welding. Hydrogen bake out is not an ASME (or other stds) requirement but it comes form welding engineer's evaluation based on good engineering practice. Some standards give recommendations for the process like AWS D10.10 suggests for carbon and low alloy steels hydrogen bake out to be performed at a temperature at least 316 degree C for 2 hours per inch of thickness with 2 hours minimum. Since post weld hydrogen bake out depends on the thickness of base metal, I suppose that's the reason the welding engineer has specified such a process only for the sch120 elbows. If low hydrogen welding consumable used hydrogen bake out is not necessary for alloy steels up to 2.25Cr-1Mo. Hydrogen bake out shall be performed immediately after welding in order to avoid delayed cracking.
Please have a look at this link: http://www.weldinguide.com/gdanastasiadis/viewtopi...
regards
wegm
RE: Another Hydrogen Bakeout Questions ASME Sect 1 work
I have read many times that as long as low hydrogen electrodes/diligent use of rod ovens/ proper baking..... were used, the risk of hydrogen related cracking is low. My question is using low hydrogen electrodes as apposed to what other types of electrodes? I have yet to see any fabricator in my industry use anything but the electrodes detailed above with the exception of some contractors using 6010/6011 to fill an open root on some low pressure carbon steel piping.
RE: Another Hydrogen Bakeout Questions ASME Sect 1 work
Incorrect. You need to specify low hydrogen by using the suffix designator, like E7018 H4 or H8.
RE: Another Hydrogen Bakeout Questions ASME Sect 1 work
RE: Another Hydrogen Bakeout Questions ASME Sect 1 work
It can be listed as "low hydrogen" because you have low hydrogen coverings, with some having low moisture absorbing capability on SMA weld rod offered in SFA 5.5, and 5.1. However, there is a note in the electrode covering classification table which indicates an electrode can be further classified by meeting specified diffusible hydrogen content by designation. To me, an electrode covering classification is much different in comparison to weld rod that is tested to meet a particular diffusible hydrogen content.
What I am saying is don’t be misled into thinking you procure low hydrogen electrodes by simply purchasing them to SFA 5.5 or even 5.1. I always require electrodes to be purchased to a hydrogen designator to ensure low hydrogen for welding.
RE: Another Hydrogen Bakeout Questions ASME Sect 1 work
RE: Another Hydrogen Bakeout Questions ASME Sect 1 work
The "Hydrogen Bake Out" is a special heat treatment with multiple variations based on several situations susch as:
Operating and Service Conditions, Type and thickness of material, etc.
We know that the Welding Activities produces high temperatures with severe temperature gradients, and rapid cooling and solidification, which increases the residual stresses, grain size, and brittleness in the welding area and the surrounding base material (HAZ), which in the presence of H2 can create a path to HIC; then the likelihood of HIC can be reduced through dehydrogenation heat treatment (DHT).
Again, based on the analysis and evaluations of the differents situations the DHT is not necessary in some cases, however can be mandatory in for some cases, this is independant of the welding process to be used.
In the Petrochemicaland oil refineries the DHT is mandatory for any material (excepting the SS) that was on H2, NH3 service condition, the intention of the DHT on theses cases is to remove service-induced atomic hydrogen prior to starting any weld.
The Welding Research Council (WRC) in their Bulletin 452 explains a little more...