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PIPE / TUBES: ASTM - API Carbon & Low Alloy Steels.

PIPE Welding Steels and TIG - MIG and Flux Cored Welds.

Every pipe welding application has unique requirements guided by different codes and specifications. The following pipe weld guide is intended as a quick reference to assist with logical welding decisions. The information provided, is certainly incomplete and implies no guarantees. All pipe and pressure vessel recommendations should be verified by the applicable codes, especially when heat treatment, low hydrogen and low alloy electrodes are required. No pipe weld should be carried out unless that weld is first qualified. If the weld is required to match the properties of the pipe ensure the alloy content of the electrode is matched and verify the preheat or post heat recommendations. With the introduction of TIP TIG into the USA, pipe shops now have a single, easy to use process that will produce superior weld results than regular TIG, flux cored or any MIG weld trasfer mode.


When welding low and medium carbon steels, the 70XX stick electrodes, E70S-3-6 MIG wires and E7XT-X flux cored electrodes can be used. When welding low alloy 1.25% Cr - 0.5 Mo or 2.25 Cr - 1% Mo with up to 0.05% max carbon, typically 8018-B2L / 9018-B3L (L = low carbon) can be used.

When welding higher strength alloys or when tempering and quenching are required to attain the higher strengths the higher carbon 8018 B2 and 9018 B3 electrodes are utilized.

For more pipe welding data follow this link

COMMON PIPE ELECTRODES

E6010 Minimum Yield 50,000 psi Minimum Tensile 62,000 psi.
E6011 Minimum Yield 50,000 psi Minimum Tensile 62,000 psi.
E7010 Minimum Yield 60,000 psi Minimum Tensile 72,000 psi.
E7018 Minimum Yield 60,000 psi Minimum Tensile 72,000 psi.

E70S-3 and E70X6 MIG Wires
Minimum Yield 60,000 psi, Minimum Tensile 72,000 psi



Ed providing MIG and FCAW process control training
to Imperial oil pipe welders on 16 inch nat gas pipe

When it comes to MIG and flux cored welding, rather than providing weld process resolutions, most pipe welding codes can cause extensive weld confusion.

Welding decision makers often look to welding codes to provide practical, pipe welding advice and recommendations. The weld reality, most codes are usually written by individuals who lack MIG / flux cored weld process, consumable and weld application expertise.

50 YEARS AFTER THE INTRODUCTION OF THE "MIG PROCESS",
AND 30 YEARS AFTER THE INTRODUCTION OF FLUX CORED ELECTRODES, THE NEWLY REVISED 2001 "AP1 CODE 582" STILL CREATES WELD CONFUSION.

API. 5.2.3 Pulsed Gas Metal Arc Welding (GMAW-P. The pulsed process may be used for any material thickness. Whenever the welding system is changed or the settings on existing equipment are "significantly altered", the fabricator should verify weld properties. The extent of verification or testing should be as agreed between the purchaser and fabricator.

WELD REALITY. In contrast to the traditional two control MIG or flux cored process, there are many weld essential variables that can be readily changed with the pulsed mode. The API code warns against a "SIGNIFICANT" change in a pulsed setting. For the weld decision maker, what is significant? From my perspective, as the pulsed mode typically provides minimal side wall fusion any "MINOR" change in any of the pulsed parameters would be significant and have an influence on the weld fusion.

While on the subject of pulsed, the API code does not discus mechanized versus manual pulsed welding inconsistencies. When a code stipulates that a fusion sensitive process is OK for any pipe thickness, the code is sending the message that this process is recommended for both manual and mechanized welds. A controlled mechanized weld weave has a lot to do with success of the pulsed process when used for pipe welds. The traditional manual weld weave inconsistency would make pulsed welding a poor choice for a pipe shop, especially when it could choose the superior weld fusion all position gas shielded flux cored wires.

THE LAST FIVE DECADES HAVE SHOWN THAT BOTH THE ASME AND API CODE COMMITTEES HAVE NOT BEEN FULLY QUALIFIED TO DISCUSS EITHER THE MIG OR FCAW PROCESS.

API. 5.2.2 Short Circuiting Gas Metal Arc Welding (GMAW-S). The use of GMAW-S shall be limited to the following conditions:

a]. Short circuit shall not be used for branch connections or socket welds.

b]. For vertical welding, the root pass and second pass progression for a material of any thickness may be either uphill or downhill.

c]. The fill and cap pass for butt or fillet welds may be welded with this process, provided the thickness of any member does not exceed 3/8 in. (9.5 mm) and vertical welding is performed with uphill progression.

WELD REALITY: There are many myths about the short circuit weld process. The codes often mention a process but are not specific about the consumables used What about the SC weld gas? Note the API code does not spell out the MIG gas mix that must be used with the short circuit process on pipe welds. Use short circuit with argon 10% CO2 and you can weld in any position and almost guarantee lack of fusion on any parts > 1/8 (>3 mm). Using mixed gas mixes, Short circuit pipe welds require a minimum of 25% CO2 and short circuit should not be used vert up or vert down on any steels over 4 mm thick.

SUPERIOR SHORT CIRCUIT WELD FUSION IS ATTAINED WITH STRAIGHT CO2. HOWEVER I BELIEVE THERE IS NO PLACE FOR THE TRADITIONAL SHORT CIRCUIT PROCESS WITH ARGON - CO2 OR STRAIGHT CO2 ON PIPE LINE WELDING IN THE 5G POSITION..

 

Ed testing the short circuit and STT process
at the difficult 5 to 7 o'clock position

Short circuit vertical down, while fine for a rotated pipe root welds can with the 5G position cause root pass problems at the 5 to 7 o'clock over head positions.

All pipe shops should remember, what's good for mechanized welding is not necessarily OK for manual welding.

In 2001, the API code makes no mention of Spray Transfer, Globular Transfer, STT or metal cored wires, does that mean they can or cannot be used?

 

The weld process considerations and confusion that now surrounds pipe welding.

QUESTION. Ed when welding pipes we could use SMAW electrodes, flux cored or metal cored electrodes, short circuit, globular, spray, pulsed transfer, GTAW the Lincoln STT MIG process or submerged arc. As much of the welding process information we get is sales driven, can you shed some light on the subject of logical weld process and electrode selection?


ANSWER. Obviously many factors have to be considered before selecting a weld process or electrode for pipe welding. Of special consideration for the root weld is the pipe roundness, and the consistency attained with the root gap dimensions. The pipe diameter, wall thickness and bevel will influence the side wall weld fusion potential. Of course the weld deposition rate potential of the process and ease of use is important. For this type of data, visit the flux cored pipe weld section for extensive pipe welding data.

Yield strength. The stress that can be applied to a base metal or weld without permanent deformation of the metal.

Tensile strength. The ultimate tensile strength, is the maximum tensile strength that the metal or weld can with stand before failure occurs.

Lamellar Tearing: When welding, the weld shrinkage stresses impose tensile strains in the steel plate or on inclusions paralleled to the plate surface. The tensile strains can separate the inclusions causing cracks. Excessive strains can further elongate the cracks. Carbon, manganese and low alloy steels made at the mill with inadequate deoxidization are sensitive to lamellar tearing. The potential for lamellar tearing increases with the amount of inclusions in the plates being welded. Of special concern is when the inclusions are parallel to the plate surface. More data in ASTM A770 / A770M Standard Spec for through thickness tension testing of steel plates.

 

Mechanical Strength of Gas Shielded Flux Cored Electrodes from the ANSI / AWS A5.29. 1198 Specifications for Low Alloy Steel Electrodes for Flux Cored Arc Welding

Hardness:The resistance of the metal or the weld to penetration. Hardness is related to the strength of the metal. A good way to test a weld after the weld and heat treatment are complete is to test the hardness of weld and the base metal surrounding the weld.

Ductility:The amount that a metal or weld will deform without breaking. Measured on welds by the % of elongation in 2 inch 51 mm test piece. An E71T-1 flux cored electrode should result in a minimum of 20% elongation. An E70S--6 MIG weld should produce 22%.

 

WELD POROSITY: Weld porosity, a cavity discontinuity that forms from a weld gas reaction. The weld porosity can trapped in the weld or at the weld surface. The porosity is typically round in shape but can also be elongated


CLUSTER WELD POROSITY. A localized group of pores with random distribution.
Causes. Arc blow, gas flow inconsistency, intermittent material or wire contamination, poor weld parameters or technique.

PIPING WELD POROSITY. The pore length is longer than it's width. Often in fillet welds the pore is seen working its way from the root towards the weld surface. Typical porosity when using argon oxygen mixes on parts >6 mm. Increase weld energy, slow weld speed avoid weaves.

ALIGNED WELD POROSITY. Linear porosity, an array of round pores in a line. Typically caused from contamination in the metal or electrode. Add energy use arc to break up surface ahead of weld.

ELONGATED WELD POROSITY ( wagon tracks). Typically found parallel to weld axis. Classic porosity when moisture is evident in gas shielded flux cored wires. Increasing the flux cored wire stick out and increasing the wire feed rate will help. Baking flux cored wires and storing wires in a dry environment also reduces potential. For MIG welding slow weld speeds, make welds larger, avoid weaves, add energy to decrease weld cooling rate.

SCATTERED WELD POROSITY. Porosity scattered randomly throughout the weld. If the weld surface is gray and looks oxidized it's typically insufficient gas flow. If the weld surface looks as clean as normal the scattered porosity is usually caused by part or electrode contamination, or weld data that causes the weld to freeze too rapidly

LARGE PORE WELD POROSITY. If weld surface is clean and does not look oxidized, the large pore MIG / FCAW porosity is usually a result of excessive gas flow, gas turbulence with gas flow greater than 40 cuft/hr. If weld surface dirty the cause is often a result of insufficient gas less than 20 cuft /hr.

PRE HEAT ALSO MEANS MINIMUM INTER-PASS TEMPERATURE

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Question: All position gas shielded flux cored consumables when used for pipe welding can provide superior weld fusion and deposit four times as much as SMAW pipe electrodes. The flux cored wires have been around for more than two decades. Ed why did it take many in the the pipe / pressure vessel industry 25 plus years to accept these great consumables?

Answer: If an organization does not have the required weld process expertise, then the management does not have the tools or confidence necessary to implement a major weld process change.

The bottom line, for decades the oil / pipe companies, power companies, chemical plants and pressure vessel shops did not have qualified weld management or qualified weld personnel with sufficient FCAW expertise to carry the process flag and lead the way.

As we are all aware, many SMAW pipe welders are often die-hard traditionalists who are proud of their SMAW skills and often less than enthusiastic to make a change to a process which requires process expertise. The SMAW welders would try the flux cored wires, and many would play around with the unfamiliar MIG equipment controls. Without optimum settings the flux cored consumables would not perform the way they were designed to perform. The stick welders would be disgruntled and resist the feeble attempts by management for a cost affective weld process change.

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STRESS RELIEVING (SR). BASIC GUIDELINES:

• STRESS RELIEF - CONTROLLED HEATING & COOLING TO REDUCE STRESS.
• STRESS RELIEF MACHINED PARTS FOR DIMENSIONAL STABILITY.
• STRESS RELIEF SLOW HEATING AND COOLING REQUIRED
• CONFIRM WITH CODE SPECIFICAIONS FOR STRESS RELIEF REQUIREMENTS.
  
  
  

Why is it rare to find anyone in a pipe / pressure vessel shop that can tell you

[a] the 0.045 (1.2mm) MIG wire feed position and weld voltage which is the starting point for spray transfer?

[b] the 0.045 gas shielded E71T-1 optimum single wire feed setting and voltage for welding 6 mm steel plate or pipe vertical up?

If an industry, in which many of it's educators, engineers and managers places little importance in weld process control training, why should we expect welders to focus on the weld process details.

 

Why in the welding industry is it difficult to find someone who knows the real cost of a MIG or flux cored weld?

If an industries focus is on on the cost of the weld wire or gas and that industry ignores the MIG or flux cored wire feed rates (weld deposition rates) attained, it's understandable when the real cost of a weld is rarely understood.

A shortage of skilled weld personel. The manager states, "how will we ever replace this aging, highly skilled welding workforce"?

TIG - MIG and FCAW Weld Reality: With all the issues that occur with with welding, managers often perceive that the welding processes are complex. Lets face it if managers have to watch their highly skilled welders and robot programmers play around with the weld equipment controls for decades, then its logical to assume that they will think the processes are difficult to control and complex.

THE WELD REALITY: Its important to note that for code quality pipe welds, the TIP TIG process is easy to learn. The majority of welding issues that occur daily in the MIG / flux cored welding shops are a result of an industry and educational system that for decades placed no focus or importance on weld process control expertise.

When training a suitable individual who has never welded, it will take no more than 3 days to train a TIP TIG welder to weld all position pipe and approx. 5 days to train that person to be a MIG / flux cored welder who can pass any weld qualification / code requirements. Consider my CD process control training resources, they are a great training aid for guys who dont want to "play around" with their weld controls..


WELD PERSONNEL WHO ARE PROUD OF THEIR SKILLS WILL ALSO TAKE PRIDE IN THEIR PROCESS KNOWLEDGE AND IN THEIR CAPABILITY IN CONTROLLING THE WELD PROCESSES THEY OPERATE.

Toughness:The ability of the metal or weld sample at a predetermined temperature to withstand a shock. The test for toughness measures the impact of a pendulum on a notched specimen. You may see that the required impact properties for the metal or weld are 20ft-lbf @ -20 F (27 j @ -29C). Some things that can influence toughness in a weld;

[] lack of fusion.
[] excess weld heat.
[] porosity in welds and laminations in the steels.
[] weld undercut.
[] incorrect weld profiles
[] incorrect weld consumables.

Fatigue: The ability of a metal or weld to withstand repeated loads. Fatigue failures occur at stress levels less than the metal or weld yield strength. Some things that can influence fatigue failure:

• Excess weld profiles.
• Welds which cause undercut.
• FCAW or SMAW slag inclusions.
• Lack of weld penetration.
• Excess weld heat, typically from multi-pass welds without inter-pass temp controls.
• Items to a part that adds restraint while welding.
• Items added to a part that can concentrate stresses in a specific location.
• Incorrect selection of filler metal, weld too weak or weld too strong.
  
  

Brittleness: The ease at which the weld or metal will break or crack without appreciable deformation. When a metal gets harder it becomes more brittle. Preheat, inter-pass temp controls and post heat all are designed to reduce the potential for brittleness.

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Malleability: The ability of a metal or weld to be permanently deformed by compression such as in a rolling or forming operation. Ductile metals are malleable.

Grain Size. A good way to demonstrate the effect of the grain size on a metal or weld. Take a full length wooden pencil, then break it in half, now break the two halves in two, try it again. You will note how difficult it is to break the smaller pieces. When we weld, the heat from the weld can make the grains in the base metal elongate, as the weld cools down the grains will get smaller. If we are doing multi-pass welds such as welding in the vee-prep of a pipe, and we don't have inter-pass, or post heat controls the welds may look good, however the high energy from the mult-pass welds may result in grain size greater than that approved by the pipe / steel manufactures. In fatigue situations, elongated grains can influence failure.

HAVE YOU EVER PURCHASED A BOOK ON WELDING?
Most welding books can be boring and few provide practical, cost effective weld data. My books are easy to read and will make you a weld process expert.

Ed, why can't we use an E71T-1 flux cored wire and weld the pipe root pass and also weld the pipe fill passes vertical down?

You could, however the flux cored process is not suited to gaps, as the arc energy is too high. When welding vertical down with a flux cored wire, you will trap the fast freeze slag which will get your QC personnel agitated

1990s: Ed Teaching Jessie, age 11,
how to do the pipe MIG root pass

Visit the MIG and flux cored pipe weld data section