Friday, August 28, 2015

13 Most Common Pipe Welding Mistakes and Best Preventions (Part 1)

A tight grasp of most common mistakes in pipe welding process and how to avoid them will benefit tremendously your process of new welder training, raising quality and productivity and improving safety.

See also:
13 Most Common Pipe Welding Mistakes and Best Preventions (Part 2)

Whether it is about welding pipes for oil and gas industries or food and beverage, there are common problems that those in pipe welding positions overseas or locally should know about and find best ways to avoid. Those problems include everything from selecting a Mig gun with too low amperage to inappropriate drive rolls and shielding gas.  Because companies have been earnestly training new welders, working with new materials, raising quality and productivity, and improving safety, it is significant to center on some of those issues in pipe welding process that may affect those efforts. Given below are 13 most common mistakes made in pipe welding and how to avoid them.

In case you are interested in:
13-Most-Common-Pipe-Welding-Mistakes-and-Best-Preventions-Part-1
Most common pipe welding mistakes with preventions

1. Forget to grind the joint after plasma or oxy-fuel cutting

Both plasma and oxy-fuel cutting processes add an oxide layer to the cut edge. This layer must be got rid of before welding because the oxide, commonly, has higher melting point than the base metal. The arc being hot enough to melt the oxide is synonym to that it’s too hot for base metal and can induce burn-through. Also, the oxides can remain in the weld, and lead to porosity, lack of fusion, inclusion and other defects of welding. Importantly, welders remember to grind the joint down to parent material before welding, and grind inside out diameters of the pipe to get rid of those oxides as well as other potential contaminants.

2. Make poor cut that induces poor fit-up and necessary gaps

When welders work on materials more subject to distortion and influences of higher heat input – for example, aluminum, stainless steel, a poor cut can be conductive to poor fit-up and produce unnecessary gaps. Then to fill it, welders compensate by placing more filler metal (hence, heat) into the joint. That added heat can induce distortion, and with such corrosion resistant pipes as stainless steel, can worsen the corrosion-resistance of the base metal. Also, it can result in incomplete or excessive penetration. Not all, poor preparation induces longer weld cycle times, potential repairs and higher consumable costs.

Currently, shops employing band saws or chop saws to cut pipe should consider purchasing specialized orbital pipe cutting equipment to ensure cuts within thousandths of an inch of specified parameters. That precision would help guarantee best fit-up and minimize the amount of filler and heat into the joint.

3. Forget to cut out and feather tacks

Tacking is crucial to fit-up, and welders are recommended to cut out and feather tacks to ensure consistency of the final weld. Specially, in shops that a fitter gears up for the pipe and somebody else welds it, it is important that the welder knows what is in the weld. The tack left in the joint would be consumed by the weld. If there is a tack defect, or if the fitter employed the incorrect filler metal to tack the joint, there may induce defects in the weld. To avoid this potential problem, cut out and feather the tacks.

4. Prepare a joint for Mig welding processes in the same way as for stick welding

Welding training is a top priority in many shops. Not few welders apply past experiences to the new job. Those experiences can be dealt with adequate training though, one common mistake is that welders with stick experience don’t understand how to appropriately prepare a joint for the wire processes in pipe welding applications. Often, those trained in stick and Tig welding prepare the joint with the heavy landing area and desire to keep the gap narrowest as possible. Because shops now turn to such easier and more productive Mig processes as Regulated Metal Deposition, they prefer that welders take down the landing area to an edge of knife and space the joint at about 1/8 inch. This area is wider than that that those trained in stick and Tig processes use, and can induce various problems – for instance, incomplete penetration, too much heat into the weld edges, not enough reinforcement on inside of the pipe. Then shops should train their welders about particulars of each application and ensure they understand weld preparation and operational techniques before they come to work.

For those who are concerned about:

5. Mistakenly believe that more shielding gas is always better

A misconception among some welders is that more shielding gas is better. They crank gas wide open, and mistake that they are giving more protection to the weld. That technique results in lots of problems like wasted shielding gas in terms of cost and resources, increased agitation of weld puddle, convection effect sucking oxygen into the weld and inducing to porosity. Each station should be equipped with a flow meter, and each welder should seize how to set and follow the recommended flow rates.

6. Count on mixing with the flow regulator

There are shops that build a separate tank of helium and a separate tank of argon for the stainless steel application that needs 75/25% of argon/ helium. Then they count on the flow regulator to bleed in the right amount of shielding gas. In fact, with this method, you won’t know what you get in a mix. Buying mixed gas from trusted sources, or buying an appropriate mixer will ensure you exactly know what you are shielding your weld with and you are following proper weld qualifications/ procedures.


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