Coding for MIG

It is more difficult to achieve a good root run with MIG that is why TIG is used.

I would expect a high number of failures in a bend test if MIG was used. Exception being when the operator can get inside the pipe and do internal root runs.

Thanks for that. I can't get inside the pipe (for most of the joints).

You've got me on the "bend test"! What is that? I can only think that you mean "stretch test", as in a hydrostatic pressure test (think aloud)!

You did not specify whether you were welding in situ or could rotate pipe sections during welding procedure. The ability to rotate the pipe makes for much easier and consistent welding. trying to do a root run upside down is not easy.

A bend test is a strip of pipe and weld cut axially from said pipe and subject to a 360 Deg bend to wit there should be no splitting or tearing of the weld to pipe area.

Forgive me I should mention if you are a certified pressure vessel welder you would have covered this procedure in your certification.

While a pressure test on the pipe might prove ok it does not guarantee the weld is up to specification if a wrong weld procedure was used.

As I said earlier the torch was kept constant. i.e. the job was kept in spindle fixture and rotated and the torch fixed. After getting the feel of welding and fine tuning the parameters, the job was done in continuous 2 runs without change of parameters in between. The bend test specimen were made as required by the code and subjected to 180⁰ ( not 360⁰) Face and Root bend. We also carried out Tensile all are through in the lab tests. No doubt we have done lot of initial trails with parameter settings ( within a limit) to achieve the root penetration.

Most important parameters are Amps, Volts, stick out, travel speed or job rotation speed, torch angle, wire size and gas flow rate . Yes, it was certified as per the code ASME Sec. IX only. Later on a periodical pressure tests were carried out and it is not mandatory.

I was replying to post 2 not 3.

Slip of the brain obviously can only be bent 180 Degree.

No. hard feeling from my end to either to garth and Beej 50. We are all same. May be in some places I am ahead, or you in some other places or ways. Whatever is required in the welding, Quality control I can help. It is just sharing the knowledge. No inferiority or show of superiority complex like some ' gurus' does.

We have trained the welders and done MIG process on hydraulic hoses used in excavators and other typical machines. If I remember correctly the size and schedule are the same and as per design of a leading USA based company and done at their associated unit in India. Earlier it was TIG plus MIG and later changed to MIG for both runs. The job was clamped in a rotary fixture and the torch in down hand - constant position. i.e., auto welded.

The root land & gap was 2.50 mm and with 50⁰ bevel angle. The wire size was 0.8 mm with 2 runs - both of MIG process. Current used was 120 Amps / 19 volts in the first and 140 or so with 19 /20 volts for second pass. The hose was subjected to hydro test and passed successfully. Trust above details are useful to you. But you have to do mock up / trails initially.

The PQR and WPQ was witnessed and approved later by Lloyds.

Ok, that gives me an idea as I have a 'tame' Lloyds inspector that I know well! I could get his opinion!

I'm still a bit worried about just MIG although a test is the right way to go anyway!

Sridhar, could you please confirm the voltage as I'm thinking that it is a little on the low side (and I could well be wrong here). I was thinking it would be up around 48v although I'm more used to 1.0mm wire!

If Mr. Beej 50 considers himself to be 'tame' then so others also in his thinking. We consider Lloyds or any Surveyor to be a professional and he will not pass the PQR / WPQ if it is not done as per the code.

Mr. Beej , you have to do lot of homework in your parameter settings and procedures. If you keep 48 volts for the current setting mentioned earlier, then you are not doing MIG welding but, .....

In GMAW process we start with as low as 16 - 22 volts ( falling under short circuit or dip transfer mode) for the current of 50 to 190 amps. Wires sizes used are 0.60, 0.80 and 1.00 mm only. This is used for semi auto or auto welding.

Even though Spray or Free flight transfer is associated with 28 - 40 volts with max. current setting of 500 amps (min.250) this mode cannot be considered for your job. This can be done with wire sizes of 1.60, 2.0 and 2.4 mm ( auto welding – we cannot handle the torch by hand) only and for a material thickness of 20 mm and above, that too only for 1G, 1F positions.

24 to 28 volts and a max. of 300 /350 amps setting is considered as Semi- short circuit or globular transfer and used with 1.00, 1.20 mm sizes. This also not for you application.

For your 1.00 mm wire it could be between 100 to 200 amps or so and with min 18 v to max. 24 volts. If you keep more voltage ( 48 v - as mentioned by you) then you can not get root welding at all . It will cut the root land and puncture it in the form of burn throughs.

Hence please do the mock - ups before final approval. I am sure U will succeed.

No, sorry about that. I personally have never used MIG for pipework. Only TIG and MMA. One of my guys uses the MIG. He's good but I fail to see how we could get a coding with that machine as it has no gauges on the front. This is why I guessed 48v (totally incorrectly)

My tame Lloyd's man! Yes, well, what I meant was we are speaking terms and could ask him a question. Other than that he is a rottweiler!

"The root land & gap was 2.50 mm and with 50⁰ bevel angle.The wire size was 0.8 mm"

I think for wire size of 0.8 mm, the root and gap must be lower than 2.5 mm. Please check your WPS's & PQR's.

We have tried with root land and gap of 1.5 to 2.0 mm. With 1.50 mm land we had burn through, at times and increased it up to 2.00 mm. Again with less root gap of 1.50 mm the penetration and fusion were in consistent. Coupled with higher rotation of the job and higher current, we settled somewhere between 1.50 mm land and 2.00 or so root gap to achieve consistency. As I said earlier the root gap and land depends upon other parameters like amperes, voltage, travel speed, stick out and torch angle helps to get required penetration and fusion.

What you say is general and what we have done is specific for that job. Kept just above 2.00 mm root gap to achieve root penetration / fusion for a land between 1.50 to 1.75 mm.

You have to keep one more thing in mind - the productivity. After gaining confidence, the welding was done in a single setting without change of parameters for the second and final run. You have to be more practical. Any small deviation from the parameters mentioned in the WPS and PQR (refer QW 255 of ASME Sec. IX) is acceptable, as long as it does not affect and vary the essential parameters. The final changes were accepted by the Surveyor and recorded accordingly.

We have tried with root land and gap of 1.5 to 2.0 mm. With 1.50 mm land we had burn through, at times and increased it up to 2.00 mm. Again with less root gap of 1.50 mm the penetration and fusion were in consistent. Coupled with higher rotation of the job and higher current, we settled somewhere between 1.50 mm land and 2.00 or so root gap to achieve consistency. As I said earlier the root gap and land depends upon other parameters like amperes, voltage, travel speed, stick out and torch angle helps to get required penetration and fusion.

What you say is general and what we have done is specific for that job. Kept just above 2.00 mm root gap to achieve root penetration / fusion for a land between 1.50 to 1.75 mm.

You have to keep one more thing in mind - the productivity. After gaining confidence, the welding was done in a single setting without change of parameters for the second and final run. You have to be more practical. Any small deviation from the parameters mentioned in the WPS and PQR (refer QW 255 of ASME Sec. IX) is acceptable, as long as it does not affect and vary the essential parameters. The final changes were accepted by the Surveyor and recorded accordingly.

1. "With 1.50 mm land we had burn through"

I think the burn through occurred due to wider root opening (gap 2 mm), and I can't believe that the wire is 0.8 mm and the root opening is 2 mm. You can reduce both root opening (gab) and root face, in this case the burn through will not happened. No one can believe that the root opening is more than the wire diameter.

2. "You have to be more practical"

I'm design manager with experience 30 years started with welding and fabrication, and I'm interested in design and fabrication of piping systems, pressure vessels, heat exchangers, ... etc. in accordance with ASME code, Section VIII, Division 1, TEMA and National Board in addition to other codes and standards in relation such as AWS, API, ASTM, .... etc. We are ASME code designers and fabricators, and we held 4 international certificates of authorization in design, fabrication, and repair: "U", "R", "NB" and "ISO 9001".

So, I think I'm more practical. Is that true?

3. "The final changes were accepted by the Surveyor and recorded accordingly"

Can you please provide me with a copy of WPS's and PQR's of that process?

OK, I think I should ask my original question again but perhaps simplified and with more detail to the specific case in hand.

I am attempting to weld 3" and 2.5" Sched 80 pipe for high pressure hydraulics (4000psi). I am currently using TIG root (1.6 wire and 110 amps. 50⁰ and 0.8 gap). Then MIG using 1mm Nickle Chrome Molly wire also 110 amps capping! I'm using mainly socket weld joints (T fillet) But there are some stabbers inserted (also, I suppose T fillet). I may need to have a few V butts.

Is there a coding for welding the specified pipe using just MIG? (I don't believe there is personally). The pipes have several bends in each 6m length so auto rotation is not an option!

Answers on a postcard to .......???????

"Is there a coding for welding the specified pipe using just MIG?"

The welding procedure by applying the 1st pass of butt (groove) joints and completing the rest of joints by MIG is good and I recommend that.

So you are kindly requested to prepare a WPS's and PQR's to prove to your self that the procedure, filler metals, joint design,......, and all welding parameters are good selected.

Mr. Beej 50,

You can follow ASME Sec. IX (or) AWS B 2.1:2005 - Specification for Welding Procedure and Performance Qualification for your MIG welding. If auto rotation is not possible try with manual welding.

Dear Mr. Galala,

With Due respect to your 30 years experience, your post as design manager and expertise in ASME, TEMA, NB and international certificates, you have to pardon me for agreeing to disagree with your views. Designing is also my favorite subject too but, I spent more time on the shop floor and seen what is practically happening there.

Your theoretical version of keeping lesser root gap, lesser land for a given size of the filler wire are all good on the drawing board. I do not expect you to agree with me also. But in general practical 90 % of the joint preparation is carried not by machining but by gas cutting, gouging, grinding etc. and you cannot get exact land size and gap as you are thinking.

Yes it is true, Your experience and expertise is much more, but still....

You can reduce both root opening (gab) and root face, in this case the burn through will not happened.

As I said earlier, we have tried all the combinations starting with 0.50 to 1.00 mm face and variable root openings starting with 0.8 mm but, settled with final figures after lot of trails.

No one can believe that the root opening is more than the wire diameter.

In theory, it is OK. We never achieve consistency in fusion and penetration in GMAW process with your thinking. You try mock up welding and then You will understand.

For example: For welding 3.00 mm thick SS plate using GTAW process with 1.60 mm size filler wire, you will design for 1.00 land and 1.00 to 1.50 mm root gap or nearer to it. That is fine on drawing board or on blue print. However, try practically and see the results. You will get the answer. It will result in lack of penetration. You require a minimum of 2.00 mm gap to achieve the required root penetration and as a designer, you know the reason also.

provide me with a copy of WPS's and PQR's of that process:

I am sorry, it cannot be done as it will be a breach of contract with my client.

I am not interested in arguing with this mater any more. Thank U.

Dear SRIDHAR,

May be your procedure(s) was being achieved, but I have to satisfy myself with seeing a documents such as WPS's and PQR's to include all details, circumstances, measurements and results.

Dear SRIDHAR

I'm still waiting any date about that welding process. I'd like to satisfy my self that there is actually a root land and root opening (gap) 2.5 mm with wire size 0.8 mm. If you don't like to send the WPS's and/or PQR's, please send a drawing sketch for that joint design. With my best regards.

Dear SRIDHAR

Welcome, my name is John Dyson. I work as a Chartered Engineer involved in the design and commissioning of pressurised plant and equipment. I am also a registered European Welding Engineer

The following site Gowelding is a very interesting, includes vessels, heads, thickness of pipes, ASME B16.5 flanges, ASME suggested forms, welding, design stresses, European codes EN288, WPS, PQR, WPQ, P-Number, preheating, welding symbols, weld failure ... etc...etc ... etc.

His owner " John Dyson" works as a Chartered Engineer involved in the design and commissioning of pressurised plant and equipment, and he also a registered European Welding Engineeris. At Mon, 03 Mar 2008, I asked him about our thread,

Quote

"The following is a such a discussion with an Indian engineer while speaking about MIG welding for a hydraulic hose, he said: "The root land & gap was 2.50 mm and with 50^o bevel angle. The wire size was 0.8 mm with 2 runs - both of MIG process".

My question is : Is that true to use a root opening up to 2.5 mm (without backing strip)while the wire size0.8 mm even with 2 runs without occurring burning.

Unquote

His reply was : If it's MIG dip transfer you will never burn will through, as the pool will freeze before that happens.