Moisture testing Low-HY

Date 05-09-2003 21:50

The moisture content of the coating can be determined by a lab with the correct equipment. It is a standard test for military electrodes.

By Niekie3 (***)

Date 05-10-2003 17:19

Hi David

Just to add to what GRoberts is saying: There is a "relatively" simple lab test described in SFA5.1 regarding the measurement of moisture in an electrode coating. In addition, there is a "diffusible hydrogen" test to test the amount of hydrogen actually deposited in the metal. This test is however very difficult and specialized.

The moisture measurement entails the following:

Flux from the electrode is placed in a crucible and weighed. It is placed in an oven at around 1000°C. Dry oxygen is passed over the specimen to carry any vapours away. This is passed through a dessicant. The change in weight of the dessicant is then the amount of moisture that was present in the flux. Obviously there is a lot more surrounding the test, like special equipment to dry and filter the gasses at different points in the set-up.

I am not clued up enough regarding the diffusible hydrogen test to describe this, but understand that it involves the collection of hydrogen from a specimen while submerged under mercury etc. (Sounded very complicated to me!) Maybe someone else on the board can give us a description of this test?

Regards
Niekie Jooste

By billvanderhoof (****)

Date 05-11-2003 05:54

I assume that the electrical resistance of the flux will change with differing moisture content. If one is prepared to do the work a test could probably be divised with equipment you could carry that would at least identify suspect rods.
Bill

By goodarc Date 05-11-2003 14:43

All you have to do rather than testing the electrodes is pop them in a house oven at 250 F for several hours. They'll be good to go after this. You can only do this once though. Be sure those electrodes that have been out of the electrode oven for too long don't make it back in, this can actually raise the hydrogen level in the oven and foul all of your rods. Hope this helped.

By R. Johnson (**)

Date 05-12-2003 12:42

If you are welding to AWS D1.1-2002 then you cannot just put electrodes that have been out in the shop for a few days back in the oven at 250F. The code says that if the low-hydrogen have been out of the oven or the original sealed container less than their allowed exposure time then they may be put in a holding oven and heated for a minimum of 4 hours before reissue.
Electrodes that have been out of the oven or their original container beyond the allowable exposure time must be redried in a baking oven. Many holding ovens are not capable of reaching the correct drying temperatures.
The logistics of good electrode control is very difficult. David has pointed out the problem of what to do when you find the welders using electrodes that have exceeded the exposure limits. This can be very expensive to justify. There are many materials where good low-hydrogen electrode control is critical and extreme measures are necessary to insure exposure limits are not exceeded.

By sayeeprasad (*)

Date 05-12-2003 09:51

Four common methods of measurement of diffusible hydrogen are
1) Gas chromotography
2)The mercury method
3) The glycerine method
4) The ethyl alcohol method.
4 is used in Russia, 3 is used by LR and is popular in Russia and Japan
However Hydrogen has a tendency to dissolve in glycerine, gas collected in this method contains other gases as well and bubbles of Hyd adhere to the glass tubes and weldment giving wrong results. Still this method is one of the most pouplar methods.
The mercury method is a std method prescribed by AWS,IIW,ASME,BS etc . In some countries this method is not used because of safety regulations. In this test a Std size sample is kept at 72 hours at 45 -100 Degrees C in an eudiometer and the hydrogen gas evolved collected over Mercury column. The evolved gas displaces Hg in the top of the column and the volume measured by the amount of displacement.
See http://www.aws.org/wj/supplement/SmithPart1-05-01.pdf gives details of the tests.
See AWS A4.3 Standard for determining diffusible hyd content of martensitic, bainitic and ferritic weld metals produced by arc welding.

In the moisture absorption test, the sample is heated in a Ni or clay boat placed inside a combustion tube in order to remove the moisture from the coating. A stream of oxygen is used to carry the mositure to an absorbtion tube where the misture is collected. The moisture content is then determined by the increase in weight of the absorbtion tube and is expressed as a %age of the original weight of the covering of the electrode~0.6% for low hydrogen electrodes . See ASME IIC, SFA 5.5, section 14 for details.

By sayeeprasad (*)

Date 05-12-2003 11:28

By CHGuilford (****)

Date 05-12-2003 13:29

David,
I'm thinking of your problem from a different aspect here. Instead of you checking hydrogen levels to see if everything is OK, maybe you should put the burden of proof on the people using the rods. The codes limit atmospheric exposure and if that is exceeded the rods should be considered rejected until someone can prove otherwise.
It is nice to know how to test for hydrogen levels but I didn't see anything listed that could be used quickly in the field.
Of course, the other side of it is that unless you have a way to know how long the rods are out of the oven, you have to take someone's word for it.
It's probably better to work with the welders so there is a mutual respect and trust, if you can. I know that is not always easy or even possible but if you can do it, then you won't need hydrogen tests. If you can't, then something simple like signing out quantity of rods and time issued might work.
Hope all works out for you,
CHGuilford

By Michael Sherman (***)

Date 05-12-2003 19:40

One system is to count the electrodes given to each welder. The welder must return the same number of stubs as he was issued. You issue electrodes at the start of the day, collect stubs and unused elecrtrodes at lunch and reissue for the second half of the day after lunch. If you are in an enviroment that requires strict control of the low hydrogen electrodes, then you already have a designated person to issue them, so this is an easy way to control the length of time they are out of the oven.

Mike Sherman
Shermans Welding

By jwright650 (*****)

Date 05-13-2003 12:13

David,
I kinda follow what CHG and Mike has said about the QC program being in place to assure that the rods are in fact being used in a timely manner and being accounted for. Maybe you could ask for a letter from the erector that his rods are being kept within the exposure limits set forth by the governing code to cover yourself (at least you could then show that you at least asked the question). In a shop environment it is a lot easier to keep up with rod exposure times than in the field. I only let our guys get enough rods to hold them to lunch, then they come back replenish their rod pouches after lunch, any left overs get put in a designated re-drying oven marked with an "R". Keep us posted on how you make out with solving your question,
John Wright

By DavidP66 (*)

Date 05-13-2003 12:52

Mike, from what I understand now, that is what is going on here...they have a strict program about this. The do only give out a certain number of electrodes at a time. So, I i think it is under pretty good control. I dont think i have to worrry about this anymore.

thanks for all the speedy replies.

David