Low-Hydrogen Electrode Control on the Job

A low-hydrogen rod is only low hydrogen until its coating picks up moisture. Then you are putting hydrogen into the weld while everything still looks fine. The bead runs well, the weld passes a visual check, and a crack may appear hours or days later. That is why rod control is a system and not a habit. A senior welder or lead knows the rules that apply to the job, runs the ovens and the logs, and knows what to do when the rules disagree.

The numbers below come from maker literature and published specifications. They are not universal. Your job's code, specification and WPS set the actual limits, and these can be much stricter than a maker's data. Always check before you rely on any number here.

What You Will Be Able to Do

• Explain how moisture in a rod can lead to cracks.
• Read the H and R markings on a low-hydrogen rod.
• Find which exposure rule applies when documents disagree.
• Run storage, holding ovens, issue logs and returns.
• Decide what to do with rods that were exposed, wet or left out.

Why Moisture Matters

The coating of a low-hydrogen rod is made to hold very little water. Any moisture it picks up breaks down in the arc and puts hydrogen into the weld pool. As the weld cools, hydrogen can collect and help crack the steel.

Hydrogen cracking needs three things together: hydrogen, a hard or sensitive area of steel, and stress. Thick plate, restraint and high-strength steels raise the risk. You control the hydrogen with dry rods and clean joints. You control the steel with preheat, and the stress with fit-up and sequence.

Maker data says moisture cracking is a particular concern with steels of 80,000 psi yield strength and higher. Lower-strength steel is not immune, so the job rules still apply.

Reading the Markings

Take E7018 H4R as an example.

The H number comes in steps of H4, H8 and H16. A lower number means less hydrogen. An H4 rod is not the same as an H8 rod, so check that the can matches the WPS.

The R means that the coating took on no more than 0.4 percent moisture after 9 hours at 80 F and 80 percent relative humidity. It is a test result. It does not say that you can leave those rods out for 9 hours on your job. Humidity on your site may be worse than the test, and your code may set a shorter limit.

Who Sets the Rule

Different documents can say different things. Work down this list, and use the strictest limit that applies unless the engineer states otherwise in writing.

Here is how far apart these can be. One maker's data sheet for an E7018 H4R rod gave a maximum exposure of 9 hours under the 2002 edition of D1.1, and 4 hours under the 2002 edition of D1.5. The same rod, in the same can, had two limits depending on the job. One state DOT spec has rods re-dried if they are not used within 4 hours of leaving the oven. Another state's spec does not allow re-drying at all.

So you do not ask what the limit is for E7018. You ask what the limit is on this job.

Storing Rods

Sealed cans. Unopened, undamaged cans keep rods dry. Store them in a dry place, off the floor. Check each can when it arrives. A dented or punctured can may have lost its seal, so set it aside and ask.

Opened cans. Once a can is open, the clock is running. Maker guidance is to hold opened low-hydrogen rods in a heated oven at 250 to 300 F. Another maker lists 225 to 300 F. Use the range in your job rules.

Holding ovens. A holding oven keeps dry rods dry. It does not dry out rods that have already taken on moisture.

• Keep the oven powered day and night, and put it where it cannot be switched off by accident.
• Use a working thermometer, and log the temperature each shift.
• Keep rod types, sizes and lots marked and apart.
• Keep cellulosic rods out. One maker says not to share an oven with them, and E6010 and E6011 rods need their moisture to work. Heating them can ruin them.

If an oven loses power, or if you find it cold, treat the rods inside as exposed. Mark them, hold them, and tell your lead. Do not assume they stayed dry.

Issuing Rods

Issue only what a welder will burn in the allowed time. Maker guidance for standard EXX18 rods is to supply welders twice per shift. A heated rod caddy at the work point can help, but only if the job rules accept it, and only if it is plugged in.

An issue log tracks rods the way a parts list tracks parts:

Write the latest use time on the caddy or tag. A welder should not have to work it out at the end of a long shift.

Worked Example: Exposure and Return

Your job allows 4 hours of exposure. If rods come back inside that limit, they need 4 hours in the 250 F holding oven before they can be issued again. That return rule is written into your job specification.

• 7:00: Rods are issued. The exposure clock starts.
• 11:00: Latest use time.
• 10:30: Rods come back with 3.5 hours of exposure. They are inside the limit.
• 10:30 to 14:30: They sit in the oven at 250 F.
• 14:30: Earliest they can be issued again.

If a welder instead brings the rods back at 11:30, the rods are past the limit. They cannot simply go back in the holding oven. Depending on the job, they must be redried under the rules or thrown out.

Redrying

Redrying, also called rebaking, drives moisture out at a much higher temperature than holding. Do it only if the job allows it, and only by a written method.

Here is one maker's published guidance:

Follow these rules:

• Use a separate redry oven. A holding oven usually cannot reach these temperatures.
• Spread the rods out. A pile dries unevenly. The rods in the middle may never reach temperature.
• Do not trade temperature for time. The same maker warns that a lower temperature for longer is not the same thing. Three hours at 500 F does not equal one hour at 700 F.
• Log every cycle. Record rod lot, temperature, time in, time out and who did it.
• Check the rods afterward. Throw out any rods with flaking or damaged coatings, or if the arc changes.

Other sources give other numbers. Some job rules allow only one redry. Some allow none at all. Your job rule wins.

Wet Rods

Rods that have been rained on, dropped in a puddle or stored in high humidity are a separate case.

One maker gives a recovery method for rods that have touched water or high humidity. It starts with a low-temperature pre-dry at 180 to 220 F for one to two hours, then a normal redry. The pre-dry drives water off slowly, so that the coating does not crack.

Some public specifications simply forbid it. One state DOT spec says that rods that have been wet shall not be used. On a job like that, the maker's recovery method does not matter. The rods are scrap.

If you do not know the job rule, do not use the rods. Mark them, hold them, and ask. A can of rod costs far less than a crack in a finished weld.

Other Sources of Hydrogen

Dry rods are only part of the job. Moisture can reach the weld in other ways.

• Damp or cold joints. Cold steel can collect condensation. Dry the joint and apply preheat as the WPS requires.
• Oil, grease and paint. All of them put hydrogen in the arc. Clean the joint.
• Rust. Heavy rust holds moisture.
• Wet gloves. Sweaty or wet gloves can wet a rod coating.
• Rain or fog at the work point. Do not weld wet surfaces. Protect the joint.

When Something Goes Wrong

Every job has a day when rods get used past their limit. The right response is to say so.

1. Stop using the rods. Take them out of the work area and mark them.
2. Find out which welds used them. The issue log tells you.
3. Tell your lead or quality contact. Do this now, not at the end of the shift.
4. Let the right person decide. The welds may need extra testing, a delay before inspection, or nothing more. That decision is not yours.
5. Fix the cause. Ask why the rods stayed out. Maybe too many were issued, or the work point is too far from the oven.

Hiding it is the worst option. A crack in that weld could appear days later, and nobody would know where to look.

Auditing a Rod Program

A quick walk-through tells you if a program is real or only on paper.

• Is every oven on, and at the right temperature?
• Does the log match what you see in the ovens?
• Are the rods in use within their time limits?
• Do the rod type and lot match the WPS?
• Are any stubs of the wrong rod type lying near the work?
• Are damaged cans set aside?
• Can a welder tell you the latest use time without guessing?

Common Mistakes

• Using the R rating as the job limit. The rule may be shorter.
• Treating a holding oven as a dryer. It keeps dry rods dry. It does not redry them.
• Putting E6010 in the low-hydrogen oven. It can damage the rod.
• Piling rods in the redry oven. The middle does not reach temperature.
• Running the oven cooler for longer. The result is not equivalent.
• Following the maker when the spec is stricter. The stricter rule applies.
• Saying nothing about overdue rods. You lose the chance to check the welds.

Check Your Understanding

Your specification has a 2 hour limit for a high-strength rod. A rod's maker bulletin mentions longer times. Which do you use?

The 2 hour limit. The stricter job rule applies unless the engineer says otherwise in writing.

A welder's rods came out at 13:15 under a 4 hour limit. When is the latest use time, and what happens to any rods still in the caddy at 17:30?

The latest use time is 17:15. At 17:30 those rods are past the limit, so they come out of use and are handled under the job rules.

A new helper wants to dry a batch of rods by leaving them overnight in the 300 F holding oven. Why does that not work?

A holding oven is not hot enough to redry rods, and more time at a lower temperature is not equivalent. Use a proper redry cycle if the job allows it.

A welder working on a roof asks for a full can so that he does not have to climb down all shift. What do you tell him?

Issue only what he will burn in the allowed time. Anything left over past the limit comes out of use, so plan smaller issues, or a heated caddy if the job rules accept one.

Key Takeaways

• Moisture in the coating becomes hydrogen in the weld, and that can cause delayed cracks.
• The H number limits hydrogen, and the R mark is a test result, not a job limit.
• Use the strictest rule that applies, and know the rule for this job.
• Holding ovens keep rods dry, and redrying needs a much higher temperature.
• Log rods out and in, and give each welder a clear latest use time.
• When rods go past their limit, stop, mark them, and report it.