Advances in Welding Consumables for Petrochemical Sector
Aniruddha Vilekar
Chief Technical Officer & Head Marketing
Ador Welding Limited

Welding is an important and critical activity in fabrication, construction and erection of any component, machinery and plant. Petrochemical and Oil & Gas industries are no exception to this. Over the years, these industries have witnessed several technological advances which have enabled them to operate more efficiently. Welding technology has also grown hand in hand with these developments and today, we have a number of welding processes, techniques, equipments and consumables to meet most of these requirements.

CONSUMABLES FOR CARBON STEELS

Carbon steels are the most widely used materials in these industries. The common consumables like E6013, E7018 (SMAW), ER70S2 (GTAW), ER70S6 (GMAW), EL8, EM12K, and EH14(SAW) have been standardized with respect to their properties and performance and are being used for many carbon steel applications in these industries for many years now. However several special consumables have been developed to meet specific application requirements .

1) Consumables for NACE applications
In Petrochemical and O & G industries a number of components are exposed to hydrogen sulphide and sour gas environments resulting in stress corrosion cracking. Weld metals operating in these environments are normally tested to ensure that they with stand these service conditions. NACE specifications TM 01 77 and TM02 84 specify suitable tests to determine the behavior of the weld metal..

2) Moisture resistant and vacuum packed electrodes
Moisture is a detrimental factor in welding since higher moisture content in the environment, shielding gas and flux, base material can introduce more hydrogen in the weld metal. Hydrogen is not a desired element in the weld metal since it makes the steel brittle In order to ensure that the electrodes, fluxes are dry at the time of usage, they are normally re-dried, particularly low hydrogen consumables. However there are many occasions when re-drying may not be possible. In order to meet this requirement electrodes have been developed which resist moisture pick up. These electrodes are designated with a suffix 'R' indicating they are moisture resistant electrodes.

In order to preserve these electrodes in the factory packed condition till usage, they are vacuum packed which ensures quality at the time of usage. the advantage of vacuum packing is that these electrodes don't require re -drying like conventional low hydrogen electrodes.

3) Weld metals with enhanced toughness requirements
Weld metal toughness is an important property. It is usually measured with the CVN impact test which specifies a minimum value for the average impact strength at specified temperatures. Specifications today, call for minimum impact values which are much higher than the standard values.

Apart from this, weld metals are today required to meet CTOD value; CTOD is a fracture mechanics test to ensure toughness of the material in the presence of a running crack. AWS specifies a separate 'J' designation for an E71T1 flux cored wire which can meet the impact properties at minus 40C.

4) Pipe welding electrodes
For pipe welding traditionally the use of cellulosic types, like E6010, has been in practice for a very long time. The use of this electrode is normally restricted to lower strength levels and for higher strength levels such as at 70000 psi, special pipe welding electrodes like E7010P1 are to be used. Electrodes are available for higher strength levels also. These are specially made for vertical down welding of pipes, (popularly referred to as stove pipe welding) particularly the root pass where penetration is of great importance.

CONSUMABLES LOW ALLOY STEELS

Low alloy steels are widely used for low, high temperature and high strength applications. Apart from the chemical and mechanical properties, today emphasis is on properties like toughness, embrittlement, creep, hot strength which are very essential for satisfactory performance in service.

1) Consumables for Cr-Mo steels
Cr-Mo steels find use in elevated temperature applications in Oil, Gas and Power industries. A number of these steels with varying amounts of Cr, Mo and other elements are used to manufacture components. While some of the grades have been in existence for a long time, many are new versions have been introduced to suit specific needs. These are;
  • Weld metals with temper embrittlement resistance
  • Weld metals with hardness control
  • Weld metals with properties after prolonged PWHT
  • Weld metal meting Inter granular corrosion (IGC) test requirements
  • Weld metals with creep properties
  • Non-Synthetic types
  • Special grades with additions of V, W, B, N, Nb, Ti
























Figure 1: FFC skid for Chemical Plant

1.1 Weld metals with temper embrittlement resistance
Cr-Mo steels get embrittled when exposed for long periods in the temperature range of 400-500C.Tramp elements like P, As, Sb, Sn are the root cause for this problem. By controlling the tramp elements it is possible to overcome this problem. This is done by using two parameters X and J factor as detailed below;









A step cooling heat treatment is also performed to determine the susceptibility of the base and weld metals to this problem. All these go to show the stringent quality standards within which consumables are being developed today to meet the industry needs.

1.2 Weld metals with hardness control
Weld metal, HAZ and base metal hardness are important factors which determine the performance of the welded joint in service. Hence in many situations the weld metal chemistries are controlled to lower carbon levels to achieve lower hardness.

1.3 Weld metals with prolonged PWHT
Most of the Cr-Mo steels are subjected to Post weld heat treatment after welding to relieve the stresses. The AWS specifications also specify the PWHT for various weld metals. But in actual practice many times the weld metals are subjected to prolonged, repeated heat treatment cycles in which the standard AWS testing may not give the correct picture. Therefore many weld metal specifications, today, specify many changes in the PWHT. In order to meet these requirements the weld metal compositions have to be adjusted to optimum levels so that the desired properties are achieved. Table 8 gives details on some of the heat treatments for a few weld metals.

1.4 Inter granular corrosion (IGC) test.
This is a test to ascertain the suitability of austenitic stainless steel material under corrosive conditions. A pass or failure in this test will forecast the behavior of the material under actual service condition. Normally the IGC test is conducted as per ASTM 262 practices like A-B-C-D-E. All these tests are different and are used for different conditions.

1.5 Creep properties
For any elevated temperature application, creep data is very important. Providing creep data for weld metal has now become a regular feature, at least for normal grades. However generation of this data is time consuming and also expensive .

1.6 Non-Synthetic types
SMAW electrodes can be made with carbon steel core wire or with alloyed steel core wire. In Cr-Mo steels, especially at higher alloy levels, it is preferable to use non-synthetic types as they produce consistent properties. Today, nonsynthetic electrodes are available even in 9Cr-1Mo types, which produce consistent mechanical properties.

1.7 Special grades with additions of V, W, Nb, N, B, and Ti
With the operating temperatures and pressures going higher and higher and with increasing concern for increasing operational efficiency, controlling emissions, super and ultra super critical boilers are being considered which use Cr-Mo steel with additions of the above elements. Materials like P91, P911, P92, P23, P22V, and P24 belong to this category. Welding consumables meeting these requirements are under development and testing. In future many power plants will use these types of consumables.















































































Figure 2: Flare for Petrochemical unit

CONSUMABLES FOR STAINLESS STEELS

Stainless steels are used widely in Petrochemical industries . A variety of grades are used and they have been standardized for many applications. The common varieties like 'L' grades, stabilized grades and their combinations have been in existence for quite some time now.

1) Duplex and Super Duplex stainless steels (DSS and SDSS)
Of particular interest to us at this juncture are the duplex and super duplex stainless steels which are increasingly used in oil and gas industries especially for components which are subjected to stress corrosion cracking..

2) 'H' versions of standard grades
The higher carbon versions of 308, 347 are now being considered for their elevated temperature properties. New weld metals with higher carbon in the range of 0.04-0.08 are now available for these materials.

CONSUMABLES FOR NICKEL ALLOYS

Nickel alloys form one of the important material groups used in these industries. Many consumables have been developed to meet the welding requirements of this group; viz; grades like;

Ni CrFe2,NiCr Fe3, Ni Cr Mo3 , Ni Cr Mo6 and many others.

EQUIPMENTS FOR PETROCHEMICAL INDUSTRIES

ADOR Welding Limited has a wide range of equipments specifically suited to the Petrochemical Industry- including machines for welding the fabricated structures, pipe networks, cooling fins, low and high pressure vessels. Special equipments are used for pipeline layout, with pipe joining and cutting. The various models of Diesel Engine operated Welding Generators (SILENT CHALLENGER Series) and Motor Generators l(SUPERGEN 320) are specifically suitable for pipe root welding with cellulosic electrodes and complete pipe welding for Hot pass, filler and capping with low-hydrogen electrodes. Multipurpose machines like the Inverter based CHAMPMULTI series and more conventional Thyristorized RANGERMULTI machines can be used for Electrode as well as MIG / FCAW / TIG Welding. Submerged Arc Welding Equipments for large diameter pipes and vessels (MAESTRO Series) along with Handling and Rotating devices like Column & Boom, Manipulators, Roller Beds, Pipe cutting and bevelling machines, Welding Carriages are present in the portfolio of ADOR Welding Automation & Process Systems Division.

CONCLUSION

Petrochemical industries offer a number of challenges for welding by constantly using improved and newer materials. This has been the constant factor fuelling the development of a host of new and modified consumables to suit the application and also the service condition. Thanks to these cooperative efforts, today we have a wide spectrum of welding consumables meeting many service requirements.

Some Ador Welding Ltd. consumables for the Petrochemical sector and the tests performed.