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PWL#069 - Pipes Underwater Flash Butt Welding, Cold Welding, Filler Metal Selection, Brazing Steel
April 30, 2009
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PWL#069 - Underwater Flash Butt Welding of Pipes, Cold Welding Steel to Nodular Iron, Brazing Stainless to Carbon Steel, Validation, Welding High Yield Steels, Certified Underwater Friction Stud Welding and more...

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May 2009 - Practical Welding Letter - Issue No. 69


1 - Introduction

2 - Article - Underwater Flash Butt Welding of Pipes

3 - How to do it well: Cold Weld Steel and Nodular Iron

4 - Welding Filler Metals Selection

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article - Brazing Carbon Steel to Stainless

8 - Site Updating: Validation, Welding High Yield Steels

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contributions: Underwater Friction Stud Welding

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board

1 - Introduction

It is a welcome infrequent event that this time an Original Contribution opens the present Issue #069 of Practical Welding Letter for May 2009. I am glad to be able to publish this work, pointing to new actual equipment used for real underwater pipe lines welding, through the courtesy of Mr. Leandros Prodromidis that represents in the USA the Paton Electric Welding Institute of Kiev, Ukraine.

Although equipment and working technology were used since a few years ago, it seems that this information is not widely available, probably because in the West it was not yet tested, evaluated and applied. It will be interesting to follow up, as news become available.

In the next section a question relative to an unusual materials and process combination is dealt with.

Readers may be interested in a recent article presenting guidelines for correct welding filler metals selection.

Brazing Carbon Steel to Stainless may be needed for certain applications: a recent query testifies to this possibility. Therefore a short note was written summarizing the most important characteristics that have to be taken into account.

The Pages of this Month added to the website, deal with Validation and Welding High Yield Steels, and are presented in Section 8, with suitable links.

A further contribution points to a recent successful application of friction welding of studs, bolts and nuts, performed underwater, approved and certified by US Naval authorities.

The other departments fall in at their usual place. Contributions, comments and feedback are welcome, as you already know. Don't use Reply. Use the Contact Us form instead.

2 - Article - Underwater Flash Butt Welding of Pipes

The E. O. Paton Electric Welding Institute of Kiev, Ukraine, developed equipment and technology to perform underwater automatic flash butt welding of pipes.

I am grateful to Mr. Leandros Prodromidis, President of PANSAT Enterprises Inc., 888 Blvd of the Arts T-1 S-402, Sarasota FL34236, USA, a Company that represents for more than 40 years the Paton Institute, who kindly submitted the information reported here.

A note added to the presentation informs that the method was also used for welding pipes in water pools of nuclear plants including that of Chernobyl.

A large part of the article by V.G. Krivenko and B.I. Kazymov which describes the essential elements of the method, is quoted hereafter with only minor editing.

"The E.O. Paton Electric Welding Institute has developed a new method for underwater pipe welding allowing to perform flash butt welding process automatically, without participation [intervention] of a welder-diver. [...]

For this purpose a special welding module has been developed. The main part of this module is a special welding machine. For the job, the machine is lowered from the vessel into the water on the prepared pipe ends, is located on them by using special video camera, and clamps both pipes. After this the welding is performed in automated mode and takes no more than 3 minutes. All these operations are done by using remote control from the vessel.

Pipe cutting and pipe surface cleaning for electrical contacts are done under water using conventional under water working equipment. The welding module was designed for welding pipes up to 325 mm O.D. and wall thickness up to 18 mm. It is of a much smaller weight and dimensions than the conventional welding modules for electric arc welding. Its electric power is 150 kW.

The weld area is protected from water during welding by using a local chamber and internal pipe seals. After the internal seals are installed, the welding machine clamps the pipes and simultaneously encloses the volume.

The water inside this volume is pumped out (displaced) by inert gas. Therefore, the welding is done in the gas volume under pressure exceeding the hydrostatic pressure created by water depth.

It is necessary to do preparation procedures before flash butt welding starts. If a new pipeline is laid underwater, pipe and pipe section ends can be prepared for welding at shore or above the water. Only preliminary rough pipe end alignment has to be made underwater.

For pipeline repair job all preliminary preparation procedures should be done under water, including washing away of soil around damaged pipe section and section removal, removal of concrete and insulation from pipe ends, pipe end fixing, preparation and electrical contact cleaning.

External and internal upset metal (flash and reinforcement) should be cut off at each weld. External upset metal is removed (if necessary) by shears incorporated in the welding head. Internal upset metal removal can be easily done on short pipe sections.

When making closure welds of long pipe sections this procedure is quite complex. To avoid this problem a special procedure is described [...].

The new welding method and equipment were tested and approved under extreme weather conditions (wind gusts of 14-16 m/s and wave height up to 5.5 m) at the Black Sea at the depth of 40-60 meters by welding pipes 219 mm O.D. and 12-20 mm. wall thickness.

Commands to perform the appropriate preliminary operations were given from the vessel by the operator. Control over these operation executions was carried out by a diver who informed the operator over an intercommunication system.

The quality of welded joints was evaluated by real time monitoring of the main welding parameters. This method is widely used in practice at construction of on-shore pipelines. Mechanical properties of joints were determined according to API Std.1104, 17th Edition.

Pipes of 219 mm O.D. and 16 mm W.T. made of St20 steel (chemical composition: C-0.18%; Si-0.27%; Mn-0.46%; Cr-0.14%) were welded in 90 sec. at optimal conditions.

Strength of welds was comparable to that of base metal (Y.S. 340-367 MPa, (average-351 MPa); U.T.S. 486-521 MPa, (average-510 MPa)).

The weld specimen rupture occurred mainly outside HAZ. Study of fractured surfaces of the specimens along weld line showed that the welded butts were of high quality. No welding defects were detected in fractures. The high quality of the joints was confirmed by metallographic investigations, which included investigations of microstructural transformations and joint zone formation.

The joints made by the new underwater welding method do not differ from the joints welded on-shore in structural transformations that occur in the weld zone, including the joint zone formation.


1. The new method allows:

  • not to use welders-divers. Assistance of a worker-diver is required at this stage only to install the welding machine on the pipe ends to be welded;
  • to raise productivity independent of the pipeline depth;
  • to improve safety of welding operations;
  • to remove limitations on the depth at which welding operations are performed;
  • to provide high quality welded joints independent of the depth at which welding operations are performed;
  • to simplify the procedure of the welded joint quality evaluation;
  • to greatly reduce the costs of repair operations.

2. The new method can be used for underwater pipe welding not only for repair purposes, but also for the construction of pipelines, e.g. to join long pipe sections to each other, to weld a pipeline end to a stack.

3. Preparation of pipe ends for welding with the new method is practically the same as for conventional underwater arc welding methods. Since the flash butt welding equipment incorporates some press units, it is possible to simplify the design of alignment devices and other auxiliary mechanisms."

Note: As this issue of PWL is going to be released, I am informed that a new and revised edition of the above information with high quality pictures is going to be made available in the near future. As soon as the relevant information is made public I will let it be known to this audience.

3 - How to do it well: Cold weld Steel and Nodular Iron

Q: Is it possible to cold weld steel and nodular iron?

A: Cold welding in general is feasible for forgeable metals having substantial ductility. Nodular iron may have a certain elongation, but is not forgeable.

Furthermore welding would not occur on graphite nodules. So that some local contact can be obtained, however without any sizeable penetration and without load carrying capability.

4 - Welding Filler Metals Selection

A thorough article explaining criteria for correct selection of welding filler metals was published at page 30 of the April 2009 issue of the Welding Journal. Although most welders would like to be able to use a table suggesting the filler metal to use, referring only to the base metal type, the article lists the many factors that influence selection.

Available welding equipment, necessary welding position, joint design, service environment and welder's skill should be known. But additional factors like chemical and mechanical properties, shape, thickness and welding procedures must be considered in order to match the filler metal to the given base metal.

Examples are given explaining the meaning of "matching" and also of "undermatching" and of "overmatching" referred to the mechanical properties of the weld metal relative to those of the base metal. Cases are offered for situations where some differences in properties may be preferred.

Penetration and backing requirements may also influence selection. Not only strength may be required but also ductility (as minimum elongation) and toughness (as Charpy V-Notch properties) at specified temperatures.

If the filler metal selection is not prescribed by codes or specifications, and especially in repair situations where local constraints may apply, careful consideration of preheat and post weld heat should be taken into account.

Dissimilar materials welding may need considering also dilution and maximum permissible heat input which may influence filler metal selection. All this may give an idea why thinking of solving the selection process simply by referring to a table of filler materials may be grossly inadequate.

Interested readers are urged to seek the complete article indicated above.

5 - Online Press: recent Welding related Articles

The Differences Between a Welding Engineer and a Certified Welder?
Note: This article may be a useful complement to my previous publication in the Mid April Bulletin ( see PWL#068B)

Laser Photonics Offers Key to Survival - Get Lean

Tips on setting up a welding shop

Robot vs robot

Eight light poles nationwide have fallen recently
(Removed by the Source: )

6 - Terms and Definitions Reminder

Microexamination means metallographic examination under optical microscope in which a sectioned surface ground, polished and etched is examined at high magnification.

Postheating is the application of heat to an assembly after brazing, soldering, thermal cutting, thermal spraying or welding for the purpose of improving properties.

Roll Spot Welding is a resistance welding process that produces intermittent spot welds, isolated or overlapping, using rotating circular electrodes. During welding, the rotation may or may not be stopped.

Substrate is the surface of the material upon which a material layer is being deposited by suitable processes.

Travel Angle defines the angle, less than 900, between electrode-axis (or gun-, torch-, rod-, beam-) and the perpendicular to weld axis in the plane of both those axes.

Unfused Flux is the portion of granular flux not being melted during submerged arc welding.

Vacuum Plasma Spraying is a plasma spraying process performed in evacuated enclosure.

Whipping is a manual welding technique in which the arc or the flame is oscillated forward and backward in the direction of travel along the welding path.

7 - Article - Brazing Carbon Steel to Stainless

A query was recently received related to brazing carbon steel to stainless.

There are different considerations and precautions that have to be taken into account, depending on actual configuration and joint details. Also production quantities will dictate the most economic assembly and heating methods.

Nevertheless different basic characteristics for the two base metals above need always be accounted for.

Coefficient of Thermal Expansion: if a metal with higher thermal expansion (like austenitic stainless) is the outer part of the joint where the inner part is a lower expansion metal (like carbon steel), clearances that are correct for allowing capillary flow at room temperature become excessive at brazing temperature.

Interchanging the materials in the same configuration (outer in place of inner material) risks to close the gap at all at brazing temperature: this should be avoided.

Thermal expansion differences should be known and used to obtain the correct gap at brazing temperature.

The brazing filler metal must be compatible with both base metals: this generally means that no brittle intermetallic compounds should be formed. If corrosion or oxidation resistance is needed, the behavior of the filler metal in service conditions should be known.

In the proposed combination above, the stainless material (depending on the actual type) has some corrosion resistance to atmospheric exposure, while the carbon steel, lacking it, must be provided with a suitable protection (oil, paint or plating).

Galvanic couplers susceptible of promoting crevice corrosion, should be avoided. The ferritic, non hardenable stainless steel type 430 is known to be subject to interfacial corrosion when brazed with most silver based filler metals. A special silver base brazing filler metal containing nickel and tin, AWS BAg-21, was developed to avoid corrosion with this material.

Thorough cleaning of the elements is required as usual before brazing. Depending on the heat application method used, a suitable flux may need to be applied because heating in air develops surface oxide that interferes with brazing.

For austenitic stainless steel (300 series type) many fluxes are suggested as suitable, differing in the activity temperature range, typical ingredients and form (liquid, powder or paste). See AWS A5.31 - Specification for Fluxes for Brazing and Braze-Welding.

Fluxes are available as commercial brands. One should select and test a product compatible with the filler metal selected and, in the case above, suitable for all brazeable ferrous metals (except those with aluminum or magnesium).

Of the different brazing filler metals available, the ones based on silver have lower brazing temperature than those based on copper and should be preferred whenever possible.

8 - Site Updating: Validation, Welding High Yield Steels

The Pages of this Month refer to topics that were already briefly dealt with in the past in old issues of Practical Welding Letter.

Validation is the process of proving that the complex of requirements necessary to assure the integrity of welding operations satisfies established criteria detailed in binding documents.

It is not enough to have a good written Quality Manual if its prescriptions are not applied constantly and completely. Validation will prove that indeed all instructions are always performed satisfactorily.

The first new page is available at Welding Validation.

Welding High Yield Steels was successful only after dedicated research efforts to develop procedures suitable to produce the minimum properties established by the US Navy. It was a proof that need and determination permit to overcome all obstacles.

The results sought were achieved and are available to this day for suitable applications. Unfortunately, for the primary purpose of building ships, the productivity was found to be too low. The lessons learnt were not wasted though, because new aims were established and later achieved with new classes of steels.

The second new page is available at Welding High Yield Steels.

Check for new pages in the Site Map or subscribe to the RSS feed using the instructions given in every page ( under the Navigation Bar.

9 - Short Items

9.1 - Activation is modifying a passive surface of a metal to a chemically active state. Also defining the chemical or mechanical process of making a surface more receptive to wetting, to bonding with a coating or to an encapsulating material.

9.2 - Equilibrium Diagram is a graphic representation of temperature, pressure, and composition limits of phase fields in an alloy system as they exist under conditions of thermodynamical equilibrium. In metal systems, pressure is usually considered constant.

9.3 - Melting Point is the definite temperature at which a pure metal, compound, or eutectic changes from solid to liquid. At this temperature liquid and solid coexist at equilibrium.

9.4 - Rib is a long V-shaped or radiused indentation used to provide resistance to bending to large sheet metal panels. Also a long, usually thin protuberance used to provide flexural strength to a forging, a casting or a weldment.

9.5 - Stress-Intensity Factor is a scaling factor, usually denoted by the symbol K,(followed by various subscripts) used in linear-elastic fracture mechanics to describe the intensification of applied stress at the tip of a crack of known size and shape. At the onset of rapid crack propagation in any structure containing a crack, the factor is called the critical stress-intensity factor, or the fracture toughness.

9.6 - Ultrasonic Welding is a solid-state welding process in which materials are welded by locally applying high-frequency vibratory energy to an overlapping joint held together under pressure.

10 - Explorations: beyond the Welder

$20 artificial knee for patients in the developing world

What is Mass Customization?

New Video on Foster Wheeler's CFB technology
downloadable from

Super Green Automotive Engine Technology

Obama's Climate Challenge: Winning the Carbon Game

11 - Contributions: Underwater Friction Stud Welding

11.1 - More on underwater welding. A short note published at page 14 of the April 2009 issue of the (AWS) Welding Journal reports on a definite underwater portable friction welding machine (a lightweight air tool) developed by a commercial company to weld studs, bolts and nuts. The special characteristic of this implement is that, according to the manufacturer, it is the only automatic stud welding machine that has been qualified and certified under Mil-Spec Standards by the Department of Defense, Naval Sea System Command. Interested readers are referred to the above publication.

11.2 - A reader wrote: "Please include articles or case studies on repair and maintenance welding." I agree that short notes based on experience could be most interesting to all.

I would be pleased to publish such information if some of the readers were ready to write and send their contributions. You are all invited. You may have reports already written, just to summarize and delete unwanted specific references.

You may use the Welding Talk page or just send a note using the
Contact Usform.

12 - Testimonials

Name: Eric Anderson
E-mail Address: removed for security
Country: United States
Introduce Your Organization: Cequent Performance Products
Describe Your Responsibility: Engineering Manager


Thank you very much for the research, it is all very helpful.


Thanks again,

On Mon Apr 13 06:19:03 2009, the following results were submitted from the "Form 5" on
Name: Nori Murthy
E-mail Address: removed for security
Country: India
Introduce Your Organization: Consultancy
Describe Your Responsibility: Consultant
Questions and Feedback : This website is very good, informative and interesting.

Thanks for the spread of welding knowledge - the keystone for the overall progress.

Nori Murthy

13 - Correspondence: a few Comments

Unexpected questions pop up sometimes. How would you describe the following?
"What are the main consequences of a poor weld preparation?"
Can you imagine to get good welding results?

Some readers ask for specialized articles or information that only research institutes or searchable libraries can provide. I am grateful for these questions, that enlarge my view of the scope of readers interests, but my help can only be quite limited.

Another reader, dealing with a very specific application, asks if international standards spell out strength requirements for those welds. Standards are not substitute for good engineering practice. It is the designer who has to establish minimum requirements for the performance of the designed product.

Another inquirer would like to know specific parameters for welding tubes, but he does not care to establish by which process. It should be understood that it is impossible to provide useful answers to undetermined questions.

Nevertheless it is a refreshing experience to see so many enquiries. I am trying to be helpful...

14 - Bulletin Board

14.1 - Int'l Thermal Spray Conf. & Expo. (ITSC)
May 4-7, 2009 - Las Vegas, Nev. USA

14.2 - 20th Advanced Aerospace Materials & Processes Conf. & Expo (AeroMat)
June 7-11, 2009 - Dayton, Ohio, USA

14.3 - If the global economic crisis threats yourself or someone near you, see how you can Create your job.

Important Announcement

For assembling at no cost your own Encyclopedia Online,
a rich collection of valuable information from expert Internet Sources, on
Materials, Volume 1,
and Metals Welding, Volume 2,
is now available.
See our New Page on Metals Knowledge.

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