FILLER METAL FOR GMAW PIPE WELDING

Date 10-11-2000 14:31

Natural gas distribution at intermadiate pressures (say 150 psi and lower) is done in Europe and Argentina (country which has an old and large experience with natural gas) using high density polyethylene (HDPE) pipes. Don't need to say the advantages of polyethylene over steel for buried pipes. The welding is also much more simple. Have you ever considered the possibility of using polyethylene for your application? If not, but are ready to do, I can send you some brochures on the matter.
Giovanni S. Crisi
Sao Paulo - Brazil

By - Date 10-11-2000 23:31

We already use HDPE for many applications but still need steel for some.

By R. Johnson (**)

Date 10-12-2000 18:04

I am not familiar with the AWS classifications that you have in your post. As far as I know there is no AWS E41010 classification for a SMAW electrode. The ER410S-x and ER480S-x classifications for GMAW do not exist. Could you possibly be looking at a mil spec or some other type of classification system.
To answer your question the low-hydrogen electrodes such as E7018 will be more than adequate for you application. Bead shape and the welding joint design will have more effect on the performance of the welded joint than any difference in tensile strength between the filler metal and base metal.

By - Date 10-12-2000 23:14

E41010 IS E6010 ; E48010 IS E7010 ; ER410S-x should be ER60S-x and ER480S-x is ER70S-x

By NDTIII

Date 10-14-2000 03:16

We use ER-70S-x for our GMAW-S welding of high pressure gas transmission lines in API-5L Grade X60 and X65. It seems to work just fine. Of course this is automated welding, and I highly recommend automated UT for inspection in order to detect any IF (cold lap) you may encounter once you get >800" t and occasionally in thinner materials.

By - Date 10-15-2000 01:24

ER70S-x does not match tensile properties of API-5L X60 and X65. You don't care about that?

By NDTIII

Date 10-17-2000 11:07

Not as much as one would think. In Table 1 of Section 5 of API-1104, note at the bottom states "Other electrodes, filler metals, and fluxes may be used but require separate procedure qualification". You see, API-1104 groups various materials by ranges of tensile strengths not matching tensile strengths. You can use any strength pipe, for instance within the ranges listed without requalifying your procedure. In some cases may even deviate (API-1104 Paragraph 5.1) from that provided it is "specifically authorizd" by the company and the PQR passes the required destructive tests and any nondestructive tests required by the company. I do not have immediate access to ASME Section II, but I believe both X60 and X65 pipe have tensile strengths of at least 75,000 psi. API groups base materials as "greater than or equal to 65,000 psi" for one group. This is the range allowed by the code. Any material above 65,000 psi is within that range, although any change in materials above 65,000 psi from that which was used for qualification, must be requalified. The bottom line is "You must qualify the procedure by means of mehanical tests". By the way, the filler metal we are using is actually ER-70S-6 (API Group 6). It has been qualified and has passed mechanical testing, NDT and hydrotesting. It is perfectly acceptable for service. If you are truly concerned about matching the tensile strengths of the pipe and filler metal, depending on the application, you may want to take a look at using A-106 Grade B (tensile strength of 60,000 psi). That is also acceptable, again provided you qualify your procedure.

By - Date 10-17-2000 21:29

API 1104, 2.4.2.6 "The compatibility of the base material and the filler metal should be considered from the standpoint of mechanical properties".

What do you do to take care of that requirement?

By NDTIII

Date 10-18-2000 03:26

There is nothing wrong with the compatability of this combination of materials. It is common practice for automated pipeline welding. When manually welding we use either E-6010 for the root and E-7010-G for the hot pas fill and cap or straight E-7010-G for the entire weld. Sometimes we use E-6010 for the root and E-7018 for the rest of the weld for X60 material and E-8018-C3 (1% nickel) for X65. That is usually for tie-ins, repairs, secondary piping or when we are just not in a big hurry. By any code they are all acceptable. API-1104 Nineteenth Edition, 4.2.2.1 "Filler metals that do not conform to the specifictions listed in 4.2.2.1 may be used provided the welding procedures involving their use are qualified". Of course we consider the compatability of our materials. Our Engineering Department approves all welding procedures.

By - Date 10-18-2000 12:21

When I read, in API 1104, 2.4.2.6 "The compatibility of the base material and the filler metal should be considered from the standpoint of mechanical properties" , I understand that the range of mechanical properties I can expect from the filler metal I intend to use shall match the range of the base metal I have to weld. Otherwise you may make a test for welding procedure qualification that will meet the minimum requirements but how can you know if the weld done on the job always meet those minimum requirements. In my opinion the only way to get confortable with that is the use of a filler metal developed to meet these minimum requirements. I would like to talk to your welding engineer to see how he deal with that.

Yvan Lessard
Montréal , Canada
(514) 992-6893

By NDTIII

Date 10-18-2000 12:55

You have to qualify your procedure anyway. Then you must write your WPS's for actual welding. You must write your WPS's within the parameter ranges of the PQR. YThat is only what the code requires. You can exceed the minimum requirements. Of course you would have to have 100% QC coverage to monitor and enforce these stringent requirements on each and every weld. That is the only way I can think of to absolutely guarantee the same results each and every time, and of course hydrotesting is the real test for fitness for service. I believe the ranges allowed by codes have already been considered and tested by laboratories and reviewed by the code committees. That is why they allow such a range of differences between base materials and filler metals.

By bspeirs (*)

Date 10-19-2000 01:23

If I remember API 1104 correctly, the weld qualification is similar to CSA Z662.

Compared to ASME IX, Z662 lets you do the tensile test with the weld cap in place. I would guess that this permits a bit of undermatch that might not pass ASME IX.

The bend tests are also not as severe, only 12.5% strain instead of 20%.

By NDTIII

Date 10-19-2000 03:11

You are absolutely correct! I am not familiar with CSA Z662, but API-1104 does not address root or cap reinforcement for tensile tests. It only addresses any notch type surface preparations that may exist from flame cutting on the sides of the specimen. In fact some pipeline projects qualify their procedures to ASME IX as it allows more lattitude in welding. Less WPS's are required. By undermatch, I assume you are talking about misalignment. This is also true, however, if I were making the test pieces for tensile tests, I would cut the areas where no mismath existed. This is to determine the material properties and not the particular weld being tested. You are going to have misalignment on pipelines. The use of a line-up clamp may help, but not always. This is a gas transmission line, Mr. Yessard is talking about, so the requirements of API-1104 or ASME B31.8 would apply. Of course a gas transmission line should receive 100% NDT as well as 100% QC coverage during fitup and welding. Thousands of pipelines are built in this manner.

By NDTIII

Date 10-19-2000 05:21

I have discussed this issue with my Welding Engineer. He has indicated that you must look at your job specification. What tensile strength is required? There is no need to match tensile strengths. Only meet what it is designed for. If the specification calls for 70,000 psi tensile strength for filler metal, then that is what you would need to use. The reason we use X60 and X65 pipe is because of corrosion allowance and not so much for tensile strength. The ER-70S-6 is perfectly compatible with the X60 and X65 pipe. You can use ER-70S-x or filler metal with a higher tensile strength if you so desire. Provided you do not change the AWS classification of the filler metal, and if you are using E-7010-G you must stay with the particular manufcturer of the electrodes used for qualification. Another example is E-7018 and E-8018 are compatible filler metals, however, E-7018 and E-8018-C3 are not. That is more important than matching tensile strengths.

By - Date 10-19-2000 20:46

Very good.I agree. Now can you ask your welding engineer his opinion, for GMAW (Z-662) pipe welding steel having 60 ksi tensile, about the use of a filler (ER70S-x) having a higher tensile (70 ksi).
I don't know if ER60S-x is available. How do you deal with that point.

Regards,

Yvan Lessard

By NDTIII

Date 10-20-2000 05:02

Again, look at your job specification. I have never seen ER-60S-x wire. If your job specification calls for 60 ksi, then you use 60 ksi pipe and ER-70S-x is perfectly acceptable provided you qualified your procedure. If 70 ksi is required, you need to purchase pipe with a higher tensile strength. Matching is not required. It is OK to have a higher tensile strength, (to a point) but not a lower. Believe me, we do it all the time. What type of pipe are you using that has a 60 ksi tensile strength? Is it A-106 Grade B? Again, if you qualified your PQR and it meets the design specification, then it is perfectly acceptable. You have nothing to fear.

By - Date 10-20-2000 14:38

The weld metal in most cases, correct me 99% of the time is 10-20 ksi higher the base metal strength. ASTM A36 ulimate load 36ksi is welded with 70XX etc.. thats almost 40k higher. However, lab testing will show the closer the mechanical properties are matched (ie 70k base metal w/70k filler metal) the better the tensile results. Go figure. I guess the mentality is, given the possibility of defects in welds, let us all use higher strength filler metal to insure the weld is stronger. I say select the filler metal with the same or slightly higher than that of the base metal strength.

So Remember: The Best Weld is "No Weld at All"

By R. Johnson (**)

Date 10-20-2000 16:26

A36 has a yield strength of 36,000 psi and a tensile strength anywhere between 58,000 and 80,000 psi. In the past it was almost always the best practice of having the filler metal exceed the tensile strength of the base metal.
The best way to know that you have selected an acceptable base metal filler metal combination is to perform a qualification test record. Tensile strength is only one consideration that must be considered for the mechanical design of the joint. Ductility and toughness of weld could be more important than the ultimate tensile strength, especially if you have a working stress design and not an ultimate stress design.

By - Date 10-20-2000 20:25

Very well. This answer my question. Many thanks.

Yvan Lessard