FCAW vs SMAW of Pressure Vessel Nozzles. 10

[JohnPB]

Our pressure vessel specifications currently do not allow use of FCAW on any pressure components. Normally our suppliers use SMAW for the nozzle installations. This adds considerable cost to our fabrication. Is there a history with FCAW in pressure vessel welding that led to its banishment from use? What can go wrong if we allow its use?

 

[unclesyd]

You have opened up a can of worms.
We don't allow FCAW on site due to one ongoing problem, Lack of Fusion in the weld. This has been and still is an operator controlled problem with all forms of MIG. We tried them all both onsite and with welding contractors and at no time could we maintain the quality we desired in a weld.
We had a lot of components that required refurbishing due to weld quality from FCAW with and without shielding gas.

Here is a website that has a lot of information om MIG welding.

http://www.weldreality.com/default2.htm

 

[pipewelder1999]

I have performed in process and final inspections on heat exchangers built for various chemical companies at a manufacturer in Alabama. They use fluxcore and solid wire GMAW. As indicated above the problems with the processes are usually operator/parameter related. Its very easy to carry a large puddle with FCAW/GMAW. Slower travel and increased heat input doesn't always lead to better fusion.

The pass thickness limitations of Sec IX apply to both SMAW and FCAW however it is more difficult to exceed this limitation with SMAW. The large puddles vs current density make it easy to have LOF. This can even be seen in SAW welds if parameters arent controlled as seen on the bottom picture here

http://www.weldinginspectionsvcs.com/WorkPictures.htm

There is also a history with FCAW Self Shielded having problems with thicker materials due to buildup of the chemicals in the wire after multiple passes. This may have been a reason.

Many field sites refuse to use FCAW. This is in my opinion based on welders not wanting to use it and therefore it never works well. The FCAW process is used for pipeline welding, building of ships, pressure vessels, structural steel etc. As with all processes, the welder is the key. I h

SMAW is my favorite process due to versatility however the production is VERY slow compared to other processes.

Here is a paper on temper bead welding using FCAW

http://www.iamot.org/paperarchive/131B.PDF

Another article that I think is by Ed Craig can be viewed at

http://www.magnatech-lp.com/images/articles/million.htm

Hope this helps.


Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[stanweld]

Many Engineering and Owner Specs also permit the use of FCAW.

In the early to mid 1970s and 1980s, a number of problems were encountered using it, especially for nozzle-to-shell attachments which were not subject to volumetric NDE. One of the problems was slag entrapment and cracking caused by welders who continuously filled the groove, instead of deslagging after each pass. Welding outside of the narrow voltage range also contributed to a variety of problems, including lack of fusion. In service found cracking of nozzle to shell welds has been common place and it was felt that improper welding technique and using FCAW were major contributors. As a result a number of Owner/Engineers banned the process altogether for pressure part welding.

Due to advancements in filler metals and power supplies and using proper welding procedures and appropriately trained welders, defect free welds can readily be achieved using FCAW.

 

[sayee1]

As usual, Gerald, unclesyd and stanweld (a star for each of your replies, I wonder why CWIC has not replied yet) have precise replies which outline why FCAW is not allowed for nozzle welds. Many client specifications (especially in India) restrict the use of FCAW even today only for external welds like welding of saddles r/f pads etc. We did try to improvise the welding of nozzles using nozzle welders which went further then the step you are planning to take, inthe sense that you are talking of semi automatic processes, while a nozzle welder would make it machine welding. Some clients accepted the practice while others did not, but showing history of the usage we could eventually shift over to FCAW. Like the earlier replies the restirction on use of FCAW for nozzle welds is mainly due to the lack of fusion defects and the NDE techniques which are used for the nozzle welds.

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
If it moves, train it...if it doesn't move, calibrate it...if it isn't written down, it never happened!

 

[CWIC]

Hi Sayee, long time...

I have been monitoring this post, but not much interested me regarding this subject. I have never encountered any restrictions for vessel attachments as long as all welding criteria was satisfied. I know when I worked for ARAMCO there was previously a restriction on FCAW-S (as noted by Gerald.) But, I do not have specific info on why ARAMCO had prohibited self-shielded FCAW electrodes (at least on specific projects) in the past. I did view some old photos of weldolets that contained [FCAW] welds with throat cracks. I'm told the welds cracked after PWHT and that is why I responded like I did in the "NDE Before or After PWHT" thread in the Mechanical Engineering Forum.

This I do know, many of the contractors I monitored while in Saudi used SMAW even when a semiautomatic process was an option. These welders consistently would produce radiographically clean welds albeit the process was much slower, all claimed their reject rate was much lower than with FCAW (S/G) or GMAW processes.

As a welder myself, I would use the most efficient process for the application. Minimizing the possibility of rework and repairs [using SMAW] IS one way to increase efficiency is the mind set.

 

[YBNORML]

Any Wire feed application should only be left for structural applications. FCAW is much too primitive for any pressure vessel, or piping application. GMAW/SMAW may be more expensive (money and timewise), but clearly produces a much higher quality weld.

 

[stanweld]

YBNORML,
I must take issue with your opinion. Literally millions of welds have been made in pressure piping systems with gas shielded FCAW without real incident. Tens of thousands of these have been subject to ASME B31.3 Sever Cyclic Service requirements and the incidence of repair has been less than that of welds made with SMAW. Pipe fabrication shops in the USA have been using the process for over 30 years. FCAW was used extensively for welding of pipe in Prudhoe Bay, Alaska piping installations both in the shop and in the field.

 

[unclesyd]

stanweld,
A long time ago when I was in Alaska the weld procedure on the pipeline was SMAW the root and hot pass, fill out with MIG (transfer arc) then cap with SMAW. After that you paid off the inspector.

As I've stated before you can get good quality welds with FCAW, but our problem and others have been consistent quality. As stated we tried everyone and every thing and the end result has always been poor welds at an unacceptable level. The problem is that the weld volume is there but it’s not metallurically bonded. The well will pass an RT and a normal UT examination. It takes an experienced UT operator to detect the areas on LF as there maybe a 80-90% good bond line. The reflection is lost in the grass if you are not careful. We proved this hundreds of times by doing a cross section and etching suspected welds. We even had a special HCL fume hood.
It was not that we were being too strict or incompetent it was that we want 99% fusion and would accept nothing less. We had the capability to do recognize these problems and manpower, in form of inspectors, to identify it.

These were our problems with C/S, there is no need to go into the problems with S/S.

 

[sayee1]

Unclesyd,
As you said in your mail "long toime ago" We have used FCAW extensively in piping and pipelines, we use FCAW as a repair weld procedure for our automatic pipeline welds. These welds are of course subject to AUT most of the times and RT occasionally. Agreed that however for pipelines, some LOF is acceptable. However what about the thousands of B31.3 piping spools we have fabricated with FCAW? Agreed again that these spools were only subject to RT and UT occasionallly and granted these welds might have had some LOF, but the spools are stil in active service without any problems I have heard of. Mind it, I totally agree with you, you can get good quality welds with FCAW, but our problem and others have been consistent quality. However I cannot agree with someone calling FCAW a "primitive" process especially in piping applications.

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
If it moves, train it...if it doesn't move, calibrate it...if it isn't written down, it never happened!

 

[CWIC]

I agree with Sayee in that FCAW will perform satisfactorily for pressure piping or vessel applications.

I would like to know what data supports the claim of:
"GMAW/SMAW may be more expensive (money and timewise), but clearly produces a much higher quality weld" This is the same position many civil/structural engineers have taken for structural applications. In these situations, the only reply I've heard for limiting welding to SMAW is "...I don't like FCAW..." I have yet to receive any valid research or test results that demonstrate FCAW process is less than adequate for pressurized weldments.

Proper workmanship and technique are key to any weld program. The current generation of FCAW electrodes are not what we used "along time ago". There are FCAW electrodes manufactured specifically for piping applications. Many of the welders I noted in my previous post had FCAW experience, but the contractors chose SMAW due to a lower reject rate. I don't think the process is the source of the repairs. But, production is certainly expected to be much higher, and that IMHO is where problems occur.

 

[unclesyd]

This is little anecdotal and windy but explains our efforts to embrace the GMAW/FCAW world. We never gave up on using the process as we tested each and every variation that came down the pike as it would have been a money saver in some cases for us. This post is just to emphasize my concern over GMAW/FCAW wasn’t something picked up or passed on, it was the result of actual experimentation and testing, NDT, Physical, and Metallurgical of which I was a major participant.

I agree that FCAW can produce an acceptable/passable weld under the proper conditions with a skilled motivated welder. I also agree that LOF is prevalent and in most cases not detected nor is it detrimental unless close to the surface or surface breaking in a non-cyclic service. A sound root and cap can carry some poor filler passes. But on a consistent basis I can achieve better results, though a little more costly, with OA (OFW), or CAW-T. I want say SMAW (BMAW) bare wire, pine block backing as its been a while.

Being close to the AWS we started to investigate GMAW at its’ introduction to the fabrication industry due to what was touted to be inherent advantages over other welding methods. I might add at this time we were welding HP Tubing C/S 2" x 1/2" wall with OA. On different recommendations we purchased equipment to try spray transfer, then globular. All efforts to consistently produce a satisfactory weld were to naught. Later we tried pulsed and short circuit again no consistent welds, we fought the gas and wire battles like everyone else. We had the capabilities of mixing and analyzing any gas mixture required and did. When FCAW came on the scene we had some C/S jacketed housings fabricated by one of the largest fabricators in the US. These are in service at 600°F cooled and cycled to 1000°F on a 21 day schedule. All have required refurbishing due failing welds. During this time the company owned a large fabrication shop where we monitored the weld quality. After much experimentation and testing they also relegated GMAW to skids and supports. The same holds true for FCAW.

Our results with FCAW-S were the same, no consistency even with extra NDT testing. Our best results, percentage wise, was with FCAW-G. It still was nowhere near the quality of welds were getting from our welders and the onsite maintenance contractor’s welders. Normal ANSI 31.3 inspection requirements wouldn’t catch enough of the problems for our service.

Our weld quality was a reflection of ours’ and the contractors’ welders. We maintained onsite a repair rate of < 0.5% and a reject rate of < 0.1%. We could put our welding program up against any in the industry. In the 42 years I was associated with the site we never had a catastrophic weld failure, though we caught a few in progress. We only encounter welding problems, as noted in previous posts, when the company started low bidding some contracts on some very large projects.

Our group had the ultimate responsibility for QC on all welding on site and supervisory control on all off site welding, this ended in mid 80's. Initially we performed all onsite NDT work in-house under the supervision of Metallurgists/Welding Engineers. We had three large areas where 100% RT was required. We also required 100% NDT inspection on all vessels (some 3000 stamped, not including boilers) on site. On most of the initial GMAW testing the NDT cost were not that much of a consideration as it was within our responsibilities so we could do the extra testing at minimal cost to a project.

When we started the FCAW testing our welding inspection QC had came under control of a Level III (5 disciplines) with a BS degree in NDT. He also carried all the Navy aviation certifications and all the API certifications as they pertain to the Chemical industry. All UT and RT work was under the supervision of another Level III (4 disciplines) with teaching credentials for other organizations.

Again I have to state this post concerns C/S only and as stated you don’t want to hear about the S/S problems we encountered.

 

[pipewelder1999]

Here is my opinion on the advantage or disadvantage. As a welder with past certifications in all of the above discussed processes I NEVER noticed one more difficult to obtain satisfactory test results with than others. Each process has advantages over others in certain situations. ALL are very sensitive to the operators knowledge, skill and desire to do a good job with the process. I would not attempt to put a root in a boiler waterwall tube in nor would I weld a circumferential seam in a 10' dia pressure vessel shell with 3/32&quot; 6010. Could it be done. Yes.

Many of the welders I have welded with and been the &quot;QC&quot; around are VERY resistant to doing something that is different from the NORM . If they are convinced by various people in an organization or their peers that a process doesn't make good welds. They are resistant to its use. I have been on jobs where A36 ductwork is being installed and the mere mention of FCAW turns into all kinds of reasons it shouldn't be used.

The problem with consistancy in my opinion is based on the operators and sometimes the equipment. The ships I rode andsubmarines I worked on were built with FCAW and GMAW hulls. The HY 80 is NOT welded with 11018 SMAW when the ship is built. The process works, However when I was in the Navy, the process was only used by the shipyard. We, the Navy welders had to use SMAW. The equipment was easier to maintain.

Anyway, y'all have a niceday


Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[deanc]

Interesting!!! Seems to come back to the welder. In most Codes you can use a gas torch and coat hangers if you qualifiy it.

Have found if the welders don't like it,it will never work right. I never did like FCAW as it is smokey,hot and nasty(and therefore never my first choice).

So,think everyone here has good and valid points. Very important to find what will work well in your particular situation.

 

[stanweld]

For field welding with FCAW, &quot;buy in&quot; from the welders is absolutely essential. On the vast majority of our construction projects the use of FCAW was abandoned for pipe welding because the welders would either deliberately sabotage the process or the expected productivity was not realized - often because the welder would not produce any more than the welders who welded with SMAW.

On projects where the welder was enthusiastic, properly trained, provided the best equipment and motivated by higher hourly wages to compensate for his increased productivity, amazing results were achieved with regard to radiographic/ultrasonic/magnetic particle verified quality and cost reductions. Sad to say, this has occured very infrequently and FCAW is primarily used by shops - both structural and pipe fabricators where most of the welds can be made in the flat (pipe rotated) and horizontal positions. Welding in these positions greatly mitigate the reduction of penetrating power when the amps are reduced as the contact tube to work distance increases outside of optimum as the welder manipulates the torch when using CV power supplies.

unclesyd,
In the past two years, we have been in evaluating FCAW for field welding of pipe with 1&quot; to 2&quot; wall thickness and have not seen any evidence of LOF from cross sectioned and microscopically examined welds.

 

[unclesyd]

stanweld,
Our experience was essentially the same as yours as we immediately realized that GMAW was unsuitable for outdoors in any sense of the imagination. Our fabrication shop was air conditioned with all the amenities for good welding. As stated before we pushed hard to put the process into production as it would be ideal for our fabrication of Jacketed piping 2&quot;-4&quot; Sch 160 Core pipe with 4&quot;-6&quot; Sch 40/80 jackets along with Class 1500 flanges in short spools. As I stated in a previous post we tried fabricating and using the filter bodies as a test bed since any failure wouldn’t cause an overhaul of the process system. A small leak of Therminol from the jacket could normally be peened closed or the specific piece of equipment rotated out. Our process, once online, requires an overhaul($150,000-$200,000) if there is any outage over 15 minutes. The process is analogist to a solid rocket motor, once you push the go button you are committed. As stated this hasn’t worked out. I checked this morning and found out that nearly all filter bodies have had some weld repair. There ages are from 18 years to 2 years old. The newest ones were welded FCAW-G by a world renown fabricator and a local fabricator. The are much larger and don’t cycle as much so it will be several years, hopefully, before anything shows up. A point that I’ve failed to mention is that we had the facilities to cycle test coupons (RT to 900°F) over a period of months that equated to years of in-service exposure. It was with this testing that we were able to detect volumetric growth in areas of LOF as indicated by UT. Another point, not quantified, was that the LOF area tended to propagate normal to the axis of the pipe. We also found that opening the grove helped in most instances though not to the extent that a narrow grove was detrimental, which is now in all books..
Another thing we noticed but didn’t fully quantify was that the younger welders tended to produce acceptable welds over a longer time span without deterioration than some of the older welders and I don’t mean many years difference in age. The physically fit make better GMAW welders than others due what we attributed arm and back weariness setting in. We found it very detrimental on weld quality try to push the welders beyond certain time periods which also varied, as note above, greatly between welders.


CWIC,
I agree that GMAW/FCAW is used on submarine piping and attachments. But the preparation and care that goes into each weld is prohibitive in a industrial setting in all but a very few instances. I think one of biggest reason for the success of this welding the absolute requirement of preheat and the close control of interpass temperatures. Adding to the fact that a good majority of these welds have RT using an accelerator instead of radio isotope. My experience has been that the sensitivy is far superior to a nuclear source. It give the UT inspector a heads up, not that he wouldn’t find a defect in the weld. Also if you noticed that the process would quickly change if there was any question as to the accessibility to a weld. Am I correct in saying the pressure hulls are still completely welded out with SAW.

I have also noted that submarines have leaks. The most notorious was on the recently decommissioned Nautilus. Shortly after it was commissioned a was discovered in an inaccessible that was subsequently stopped by addition of several drums of BARS stop leak. The leak stayed sealed for the service life of the Nautilus.

 

[EdDanzer]

Most interesting thread. We weld hydraulic cylinders the work at 4,000 psi and see pressure spikes high enough to exceed the 75,000 psi yield. We now use 90,000 psi yield and have seen a few barrels yielded. The only weld method we found to last is to use an .035 diameter E80SD2 solid wire, 75/25 shield gas and ¼” max bead size, and multiple passes. Larger weld size, larger wire, all reduced fatigue life.
The biggest problem with wire is controlling the shield gas. Unless there is good shielding, welding outside is not possible. If there is a gap between the parts, air contamination from the gap can be a problem.
Welders typically don’t like changing processed, someone who is good as flux core, usually doesn’t do well with solid wire or stick.

 

[JTMcC]

The welders are often critisized for not embracing a new or different process but one thing alluded to by unclesyd plays a major role in my opinion. Take a super flexible whip on a SMAW machine, and compare it to a FCAW gun. Then manipulate both, as precisely as possible, in all positions, for 10+ hours per day. You WILL gain insight : )

JTMcC.

 

[nickt1960]

My experience with the oil and gas construction industry is that FCAW has long been seen to have suffered from lower impact properties than the other processes - to me that is the prime reason from excluding it from may specifications, especially self shielded.

Whilst the consumables have now come a long way to rectifying the above reputation, caution must still be used if the piping or vessel requires PWHT, as the impact properties drop away very dramatically after stress relief.

In summary, I will permit FCAW processes on B31.3 piping as long as PWHT will not be required.