Recent Developments in SMAW Consumables and Future Challenges
The Manual Metal Arc Welding process continues to dominate the industry and is still being widely used by the fabricators, even though the percentage of weld metal deposited by this process is declining and is slowly being replaced by the automatic and semi automatic welding processes.
The welding electrode industry in India which produced its first electrode in the year 1943 has grown and advanced both in terms of size as well as technologically. The growth and technological achievements were too rapid, that within a short span several indigenous electrodes replaced the imported ones thus conserving a sizeable amount of foreign exchange on one hand and making it easier for the fabricators to fabricate new and sophisticated jobs on the other hand without having to depend on the imported electrodes.
It can be said with certainty that the electrode manufacturers in India have always been enthusiastic and had the spirit to face the challenge of the fabricators in developing and standardizing new consumables.
Thanks to the constant support of the fabricators, the challenges continue to flow to the consumable manufacturers and the developments of new consumables and achievements are seen frequently in this field.
The SMAW process as said earlier is widely used for the fabrication of a variety of materials right from carbon steels to Ni & Ni base alloys. The following pages detail briefly the recent developments in the SMAW consumables and the challenges of the future.
2.0 LOW HYDROGEN ELECTRODES
It is worth observing that the common mild steel low hydrogen electrodes like E-7016, E-7018 & E7018-1 were developed and introduced as early 1962 and since then these electrodes have been used by the fabricators in fabricating several critical components with extremely satisfactory results.
Therefore, recent development in these types is introduction of moisture resistant electrodes with vacuum packing. All these types are well received by the customers and understood its advantages.
Some of the typical requirements to be met in this class are shown in table-1.
2.1 CONSUMABLES FOR OFF-SHORE APPLICATIONS
Indian manufacturers responded quickly to the off-shore requirements with suitable consumables. Meeting AWS Specification alone is not sufficient, since the customers/consultants specifications vary widely and are more stringent. It has to meet stringent requirements of HIC & SSCC tests as per NACE standards.
All these consumables developments are a classic example of the close co-ordination between the user and inspection and manufacturing agencies and the higher technological standards attained by the Indian electrode manufacturers.
Some of the latest customer requirements are shown in the Table-2.
3.0 LOW ALLOY STEEL ELECTRODES
The increasing use of low alloy steel material for high temperature, low temperature and high tensile service and the continuous development of new steel, with specifically enhanced properties have led to the development of several new types of electrodes.
A reference to the AWS SFA 5.5-1996 and 2006 will reveal that 27 new consumables were introduced and it clearly speak of the rapid pace of standardization of low alloy steel electrodes. Apart from the standard type electrodes there are now a host of low alloy steel electrodes which are tailor-made to suit the specific composition and mechanical property requirements.
Some of the significant developments are shown in Tables-3 to 7
4.0 STAINLESS STEEL
As we know that the hydro-turbine runners are made up of SS-410 Ni Mo type martensitic stainless steel [13% Cr, 4% Ni and 0.5 % Mo] castings. Welding is used for the assembly and repair of casting defects. Suitable consumables are developed by Indian manufacturers to meet stringent requirements of hardness and toughness. These consumables are specified even for repair of worn out runners because of
(a) The erosive action of water flow
(b) The abrasion of solid particles in the moving water with themetallic surface.
(c) The corrosive action of water.
The details of the party’s requirements are shown in Table-8
4.1 DUPLEX STAINLESS STEEL
The demand of Duplex stainless steels is increasing day by day for their applications in Oil and Gas fields; Chemical and Processing; and Paper and Pulp industries because of their increased strength and improved corrosion resistance which are not readily attainable by conventional single phase ferritic or austenitic stainless steels. Indigenous products are not only standardized to meet AWS requirements but also it was fine tuned to meet specific requirements.
Some of the customer requirements are shown below:
Special Requirements apart from AWS class are shown below
Ferrite : 30 to 55 FN
Hardness: [Weld] : 300 HV10
CVN Impact : at +20oC 45 Joules Min & at -40oC 35 Joules Min
SSCC : at 24oC with 350 N/mm2 stress
: at 90oC with 325 N/mm2 stress & 16 bars partial pressure
Test Criteria : Test sample failure at or after 720 Hrs.
PREN No. > 35 (PREN No. %Cr + 3.3(%Mo) + 16(%N)
5.0 Ni AND Ni BASE ALLOYS
In the past because of non-availability of suitable wires Indian manufacturers used to produce Inconel types with Ni wires and it has got its own disadvantages. But all these consumables are fully tested and standardized to meet stringent requirements even at -196oC impact and lateral expansion. One of the typical customer specifications is shown in Table-9
6.0 PACKING OF ELECTRODES
Electrode packing has always been one of the popularly discussed subjects whenever an electrode manufacturer meets a fabricator. Damaged cartons, torn off polyethylene bags create problems in the use of the electrodes and their quality deteriorates, especially when they are to be stored for quite some time in that condition before they are used.
To a great extent these problems have been overcame by the leading electrode manufacturers who had to carry out a lot of modifications and experiments before arriving at a solution.
The electrodes are now supplied with LDPE, HDPE & vacuum packing to ensure that the electrodes reach the user in good condition. Suitable polyethylene covers inside and outside the carton and outside the shrink wrapping of box ensures the quality of electrodes.
i. Sophisticated vacuum pack machines are being used to meet stringent vacuum pack requirements and increase productivity.
ii. The pouches, which are used, have got three layers. (PP layers minimum 12 micron, Aluminium foil layers minimum 12 micron, polythene layer 98-110 micron.)
iii. Once the vacuum pack sealing is over, the cartons are checked for any leakage and clear for further packing.
For proper identification and traceability even they are supplied in different colours.
7.0 FUTUTRE CHALLENGES
The Indian electrode manufacturers having faced several challenges in the past with the development and marketing of several electrodes look at the future which has several challenges of a mixed nature. The higher productivity at economical cost does not permit the use of SMAW in many cases.
Facing these retarding forces and increasing stringency of quality requirements from customers, the Indian electrode manufacturers’ step into future. There is a lot to be done both technologically in terms of development of new types as well as commercially with a view to reach customer at an economical cost.
There are so many manufacturing units who are producing popularly known as E-6013 types. While on one hand, the technological advancement and the increasing number of manufacturing units is a welcome sign on the other hand there are several associated problems related to quality.
Therefore is the importance of making ISI certification [BIS License]. Efforts should be made to see that all the plants including those of the small scale units are certified by ISI.
7.2 Low fume electrodes
The effect of welding fumes on the welder and environment has been discussed at length in various seminars. Efforts have been made by the electrode manufacturers in reducing the fumes to a low level and many of the common types of electrodes are now formulated in order to produce minimum fumes.
On this subject it will be relevant to highlight the importance of other facilities like good ventilation, de-fuming/de-smoking apparatus etc. for providing a healthy environment to the welder. The formation and the activities of the OHS, Trichy are a welcome one in this direction.
7.3 Nil Ductility transition temperature data
Proper data to be generated for the consumables especially low hydrogen carbon steel & low alloy types even though still CVN toughness is still continuing. This data is required by off-shore drilling platforms, some of the nuclear components etc.
7.4 Creep Data
It has become essential to develop creep rupture data for the recent developmental consumables to ascertain its suitability. Co-coordinated efforts between user and manufacturer are important to carry out these tests since it is a time consuming test.
7.5 Step Cooling Data
As we know the temper embrittlement needs to be studied for the weldment. Enough literature is available on this subject and procedures are established at both fabricators’ & consumable manufacturers’ end. There is a challenge for manufacturers to generate data and submit to the fabricators for consideration.
7.6 17-Class Stainless Steel Products
17 class electrodes is a modification of 16 class covering. 17 class produces spray arc and a finer rippled weld bead surface. The finish need not demand further machining. But it needs proper baking before use at 300oC for 1 hr to avoid starting porosity. This is another challenge at the users end.
Apart from development and improvement of SMAW consumables, it is equally important to educate how it is used at user’s end. It can be said with certainty that the successful development of an electrode and its acceptance can only be possible if it is used carefully at fabricators end.
7.7 Users’ support
The development and standardization of new and improved consumables is possible only with constant support of the users including consultants, inspection agencies etc. Unless the electrode manufacturers are given details of the requirement of the electrodes and also the feedback on the consumables developed, it will not be possible to develop suitable types.
The interest shown by the users in developing suitable indigenous consumables for their requirement has been excellent and thanks to their efforts which are responded by the electrode manufacturers who meet the challenge of developing suitable consumables. This coordinated effort must continue and Indian manufacturers should be given an opportunity and encouragement to develop suitable equivalents.
The SMAW consumables have been developed with a rapid pace which is primarily motivated by the development and use of new steels, improvement in quality standards, performance characteristics. Most of the applications are converted in to automation. With the increasing use of the automation higher productivity, the use of SMAW process is on the decline. The users also have to meet challenges in SMAW consumables in terms of their proper storage and use. A coordinated effort from the manufacturer as well as the users will go a long way in improving the standard, and achieving a better result.
TABLE-1: E7018-1 H4R with special requirements.
Mn+Cr+Ni+Mo+V: 1.75 Max
Diffusible hydrogen: 4 ml/100gms of weld metal (Max)
Moisture: 0.3 as received or Conditioned
0.4 as exposed (27oC, 80 % RH & 9 Hours)
PWHT: SR at 600-640oC for 4 hrs
TABLE-2: Offshore requirements
HIC Test : CSR ≤ 0.009 & CLR ≤ 10.00
SSCC Test : At 72 % of YS
“Time to failure’ shall not be less than 720 hrs”
TABLE-3 : Special properties demanded by the fabricator
* Ti, Cb+Ta, Co : To report
Fe : Balance
Ti + Cb + Ta + Cu + Co : ≤ 0.25%
Diffusible hydrogen : 4ml/100 gms of weld metal
Preheat : 150oC
IPT : 250oC
PWHT : 552 ±10oC / 195 minutes
H/R : 55oC/ 1hr Max
C/R : 55oC/ 1hr Max
Nil Ductility Transition Temperature
Specification: ASTM E208
Specimen Type: P1
Testing Temperature: -46oC to +20oC
Fracture toughness test as per: E1820
TABLE-4: WB-36 Material Composition and Its Properties
TABLE-5: P-91 consumable specification
PWHT: 760oC for 2 hours
PWHT: 760oC for 2 hours
Table-7: Special Properties Specified By One Of The Customer
Heat treatment: SR at 690oC for 3 hrs
Normalizing at 940oC & Tempering at 720oC
TABLE-8: 410NiMO (MSS Consumable requirements)
Heat treatment: SR at 600oC for 3 hrs
TABLE-9: INCONEL 182
Base metal: SA 387 Gr 11 Cl 1 + SA 240-410S
Application: Weld overlay and clad restoration
Preheat: 150oC Min
IPT: 315oC Max
Rate of heating: 75oC Max for 1 hr
Rate of cooling: 95oC Max for 1 hr
Holding temperature: 705oC Min
Holding time: 145 minutes Max
CVN at 0oC: 60 J Min (avg)
Min acceptable for one specimen: 50 J
Hardness: 241 BHN Max
Chromium Content: 13.5% Min
All other properties are as per ENiCrFe-3 classification