GB2083394A

GB2083394A - Shielding paste for arc welding, especially underwater arc welding

Info

Publication number: GB2083394A
Application number: GB8121976A
Authority: GB
Original assignee: PELKONEN HEIKKI
Current assignee: PELKONEN HEIKKI
Priority date: 1980-07-15
Filing date: 1981-07-15
Publication date: 1982-03-24
Also published as: GB2083394B; NO155481B; SE8104352L; FR2486843A1; FI802244A; DE3128000A1; FI67188B; IT8167973A0; JPS5739093A; NO155481C; CA1167605A; FI67188C; NO812416L

Abstract

A shielding paste especially suitable for underwater welding comprises a) a vehicle based on one or more long chain aliphatic acids b) amorphous phosphorus and/or magnesium as an illiminant; and c) iron oxide and/or magnesium for the removal of hydrogen. Aluminium powder may also be included. The vehicle is preferably a mixture of oleic, stearic, and palmitic acids with glycerin. Welding with rod or stick electrodes and SMA, MIG, MAG, TIG and plasma welding are referred to.

Description

SPECIFICATION Shielding paste for welding, especially un derwater welding The present invention provides a shielding paste for use in arc welding and especially in underwater welding.

Undertakings that carry out welding work and manufacture welding equipment and supplies have attempted to achieve, for their own use and/or to offer for sale, a welding method and equipment which would enable welding to be performed independent of external conditions. It is generally recognized that arc welding, especially the gas-shielded method which is simple to use in good external conditions, is not successful in windy, draughty, rainy and/or damp conditions, not to mention the conditions in underwater welding.

Underwater welding has been the subject of growing interest and development work in recent years. Underwater welding has been used principally in repair work on drilling platforms, underwater gas and oil pipelines, ships and habour installations. The structures welded have generally been such that it would be impossible or prohibitively expensive to raise them to the surface. The aim in underwater welding has been to achieve welds of high quality.

Known methods of carrying out welding underwater may be divided according to the welding environment into two main groups: wet methods and dry methods. Known wet methods using stick welding generally employ ordinary welding electrodes which have been given a waterproof coating of vinyl paint or paraffin wax to prevent them getting wet. In wet methods using a gas-shielded arc, besides the conventional equipment a welding tool is used in which a jet of water is projected in the form of a hollow cone from an outer annular orifice in order to keep the water out of the region of the arc. A water jet has been used with relatively good results in the CO, wet method. In wet methods, as implied by the name, the water has unhindered access to the region of the arc.In dry methods the water is prevented from reaching the region of the arc by covering it with a welding guard which is essentially closed (although, of course, the joint being welded must be left clear) or else open at the bottom, and which may be either transparent or opaque. With welding guards that are open at the bottom the welding tool is generally inserted from below; with the small, completely enclosed type, the tool is inserted through the wall. If the welding guard is sufficiently large the welder can work inside it. The atmosphere inside the guard may be either a shielding gas or air.

In underwater welding by dry methods almost the same quality of welding can be achieved, at least at small depths, as when welding in air out of the water. The dry methods, however, suffer from the drawbacks that fixing the welding guard in place and moving it are time-consuming, and that welding with a guard is an inconvenient and inflexible process. Moreover, in many places it is not possible to use a welding guard.

Wet welding, with which this invention is concerned, is a very flexible and economic way of carrying out underwater welding work.

It can be carried out using, apart from the necessary diving gear, the same equipment as is used for welding on land. The weld quality achieved by wet methods, however, does not approach the results obtained by dry methods.

Three factors detrimentally affect the quality of the weld, and each of them is a conse quence of the surrounding water. They are high cooling rate, high hydrogen content, and the ambient pressure, which particularly at greater depths affects the reactions occurring in the arc and the deposit of material, and also affects the the reactions between the melt and the slag.

The most serious problem in wet methods is the occurrence of hydrogen-induced cracks, which is the result of the high hydrogen content which is taken up by the welded join.

The problem is worsened by the high cooling rate, which reduces the diffusion of hydrogen out of the welded join, and the impracticability of using pre-heating or after-heating for the removal of hydrogen, stress reduction or the avoidance of brittle microstructure. As a consequence of the high cooling rate, structural steels frequently develop a microstructure with high internal stresses and a tendency to embrittlement.

Another significant problem in the wet methods is the poor impact strength of the welded joint. The ambient pressure, especially at greater depths, affects the conditions of the slag reactions. Moreover, the rapid cooling means that the kinetic preconditions for sufficient cleansing of the weld material are not met.

Especially in rod welding by the wet method, the avoidance of weld defects such as porosity, slag inclusions, slag line and joint or root defects requires great skill while working under difficult conditions.

The purpose of the shielding paste of the invention is to eliminate the drawbacks hitherto associated with wet methods of welding and to achieve a shielding paste which is suitable for arc welding performed in water or other liquid and in air. The new shielding paste comprises a) a vehicle based on one or more long chain aliphatic acids b) amorphous phosphorus and/or magnesium as an illuminant; and c) iron oxide and/or magnesium for the removal of hydrogen.

The basic components of the shielding paste of the invention are the vehicle or base, an illuminant (which makes working easier), and a substance for the removal of hydrogen.

The base is preferably formed of one or more and preferably all three, of oleic acid, stearic acid and palmitic acid which may conveniently be mixed with glycerin.

The illuminant can be phosphorus, and iron oxide can be used for the removal of hydro gen. Magnesium can be used both as an illuminant and for the removal of hydrogen.

A little aluminium powder can be mixed in the shielding paste when welding stainless steel and using austenitic electrodes.

In the recommended form of application of the invention the base contains 41-60% by weight of oleic acid, 8-21% by weight of stearic acid and 20-30% by weight of palmitic acid. In addition it may contain 1-4% by weight of myristic acid and/or 1-10% by weight of linoleic acid.

The amount of amorphous phosphorus used as an illuminant is dependent on the depth of working and visibility, but is generally about 2-10% by weight of the base.

A suitable amount of the iron oxide used for the removal of hydrogen is about 4-6%, for example 5%, of the weight of the base.

Magnesium can be used both as an illuminant and for the removal of hydrogen, in which case the amount present is suitably about 5-15% of the weight of the base.

By a substance introduced into the region of the arc and/or by a substance which together with water forms a liquid, fluid mixture, solution or such like which conducts electricity, an attempt is made to facilitate the controlled burning of the arc, to achieve a larger weld melt, to retard the cooling of the weld and to limit the direct presence of water in the region of the arc and its contact with the weld melt.

In use of the invention electrically conducting material in the region of the arc facilitates the striking of the arc and its burning in water. On burning it forms a shielding gas zone, preventing water from reaching the arc and the melt. Such a shielding gas zone is formed especially when using organic substances. Moreover it forms a layer of slag, which protects the melt from the action of the water when there is so much of the substance that it is not entirely consumed in the arc.

This additional layer of slag formed by the substance retards the cooling of the weld and thereby improves the separation of gases from the weld. Due to the slower cooling it is easier to obtain a satisfactory weld shape. The substance affects the melting speed and penetration. The melting speed and penetration are improved particularly when using organic substances, which on burning in the arc produce considerable quantities of thermal energy.

In welding tests with shielding paste according to the invention, excellent results have been achieved. The reasons for this are not fully understood. Another factor retarding the cooling of the weld, in addition to the protective effect of the auxiliary substance, could be that as a consequence of the use of the auxiliary substance electrical currents are formed outside the actual arc, between the electrode and the whole of the object being welded, thereby heating the object, water which may possibly be in its vicinity, and the weld seam together with the slag layer and the additional layer of slag. The weld would then remain hot longer, improving the escape of hydrogen and thus reducing hydrogenembrittlement, with a resulting strengthening of the weld seam.

Welding performed underwater with the shielding paste of the invention can be classed as a wet method, because the water together with possible additives has almost unrestricted access to the region of the arc.

The method is suitable for use with all types of arc and gas arc welding methods, such as rod (stick, SMA) welding, MIG, MAG, TIG (GTA), Arcatom and plasma welding. The equipment and apparatus required vary according to the welding method chosen.

The description given below is primarily concerned with underwater welding, because arc welding underwater currently presents the greatest problems. Nevertheless, it is possible to use the method for arc welding performed in other external conditions, for example in connection with arc welding which is performed in air. In this case the electrically conducting substance and/or the substance which together with water forms an electrically conducting liquid, fluid mixture, solution or such like prevents the harmful effects of air as well as water on the weld. When the shielding paste is used in connection with arc welding performed in air, the formation of fumes is greater than when it is used in connection with underwater welding. In this connection mention may be made of an application of the invention in which the normal shielding gas used in arc welding is replaced by a paste which protects both the arc and the weld. The paste is extremely suitable for use in connection with arc welding performed in both water and air, the paste protecting both the arc and the weld.

Methods of use of the paste according to the invention are described in the following with reference to the accompanying drawings.

In Fig. 1 the arc 1 is struck between the welding electrode 9 and the base material 13.

At the same time the welding electrode 9 melts and forms the weld 10, which fuses with the base material 13. As the weld 10 is formed, the coating of the welding electrode 9 creates a slag layer 11 on top of the weld.

The paste 2 according to the invention is introduced through tube 12 into the region of the arc 1.

In the application represented in Fig. 2 the paste 2 is introduced to the region 14 of the arc 1 via an annular nozzle 4 which surrounds the welding electrode 9 and the arc. The paste causes the region of the arc to become electrically conducting. This method resembles gas-shielded arc welding (MIG, MAG, TIG), but with the paste of the invention in place of the gas. The annular nozzle can, of course, extend to the filler wire. The use of shielding gas in addition to the paste is, of course, possible. Such gas can be introduced via the annular space between the inner wall of the nozzle 4 and the outside of the electrode 9.

Fig. 3 represents an application in which the arc 1, which is formed between the welding electrode 9 and the base material 13, is partially protected by a paste 3 according to the invention. In the region of the arc a substance is given off by the paste 3 which dissolves and makes the water in the region of the arc electrically conducting; the welding takes place under water with water surrounding the object being welded. As the welding proceeds the paste 3 is moved along behind the arc as the weld is formed, so that the arc burns in the hollow 7 formed by the piece of paste. The paste 3 also deposits a protective layer 8 on the weld 10. The protective layer 8 retards the cooling of the weld joint 10 and inhibits contact between the water and the weld joint.Furthermore, the paste 3 remaining on the hot weld joint 10, being an organic substance, continues to burn even after the arc, and this is conducive to efficient prevention of excessively rapid cooling of the weld.

The application of the invention to a welding electrode 9 is represented in Fig. 4. In this a conventional, either coated or bare, welding electrode 9 is additionally coated with a paste 3 which gives off and/or dissolves in the region of the arc 1 a substance making this region electrically conducting. The hollow 7 can, of course, also be enclosed by the paste on the open side of the gap being bridged by welding, in which case the arc is essentially in a closed space.

The application of the invention is not limited to the specific examples given above.

Thus, for instance, the guides for the auxiliary substance used in the welding and which are part of the welding equipment used, may consist, for example, of an annular nozzle or similar partially or preferably completely encircling the electrode rod or wire, or of one or more tubular or other nozzles or such like located in the immediate vicinity of the electrode rod or wire. Further, the auxiliary substance may be fed by means of a piston, centrifugal or diaphragm pump or other such pump or such like feeding device or other feeding device, as, for instance, a screw feeder or similar.

Claims

1. A shielding paste for use in welding and especially in underwater welding by wet methods, comprising a) a vehicle based on one or more long chain aliphatic acids.

b) amorphous phosphorus and/or magnesium as an illuminant; and c) iron oxide and/or magnesium for the removal of hydrogen.

2. A shielding paste according to claim 1 in which the vehicle contains one or more of oleic acid, stearic acid and palmitic acid.

3. A shielding paste according to claim 2 in which the said vehicle contains all three said acids mixed with glycerin.

4. A shielding paste according to claim 3, in which the vehicle contains 41-60% by weight of oleic acid, 8-21% by weight of stearic acid, and 20-30% by weight of palmitic acid.

5. A shielding paste according to claim 2, 3 or 4, in which the vehicle additionally contains 1-4% by weight of myristic acid and/or 1-10% by weight of linoleic acid.

6. A shielding paste according to any one of claims 1 to 5, which contains 2-10% of amorphous phosphorus, expressed as a percentage of the weight of the vehicle.

7. A shielding paste according to any one of claims 1 to 6, which contains 4-6% of iron oxide, expressed as a percentage of the weight of the vehicle.

8. A shielding paste according to any one of claims 1 to 5 which contains 5-15% of magnesium as an illuminant and for the removal of hydrogen, expressed as a percentage of the weight of the vehicle.

9. A shielding paste according to any one of claims 1 to 8, which additionally contains aluminium powder.

10. A shielding paste according to claim 1 substantially as herein before described.

11. Method of welding in which a shielding paste as claimed in any of claims 1 to 10 is used.

12. Method according to claim 11 substantially as herein before described with reference to any one of the Figures of the accompanying drawings.

13. Method according to claim 11 or 12 in which the welding is effected underwater by a wet method.

14. Welds produced by the process of any of claims 11 to 13.