Best Welding Practices.pdf

UNCONTROLLED INDIEN GEPRINT BBS handleiding/werkinstructie 04.00.2030

Wec : Nee Comm. Index : B / C Veiligheidsrapport : Nee Risico : M WWW-Aannemers : Ja Classificatie : Unrestricted Noodplan : Nee HSE kritisch : Ja SOX gerelateerd : Nee

HANDLEIDING/WERKINSTRUCTIE:

BEST WELDING PRACTICES (PERNIS/MOERDIJK)

Doel / scope To give background information/rules for the best practices of welding, experience gained from the past. It is a supplement for DEP 30.10.60.18 GEN Welding of metals, in which this part is deleted. In BBS doc 04.00.4052 Amendment to DEP-Gen requirements and reference are given to this doc.

Doelgroep Materials, Corrosion & Welding Engineers, Inspection, Welding Inspectors, Shop, Contractors.

Toetsers CEI/2, REA/3

Risico M. Het niet opvolgen van deze werkinstructie heeft als consequentie dat best practices niet worden gebruikt.

Revisie info Laatste revisie

Datum Reden

A 23-12-2008 First issue Meer revisie info

Inhoudsopgave 1. ACTIVITEITENBESCHRIJVING.......................................................... 3

2. REFERENTIE...................................................................................... 3

3. BEST WELDING PRACTICES GENERAL.......................................... 3

4. WELDING QUALITY ........................................................................... 4

5. WELDING OF CARBON STEELS WITH UTS < 490 MPA................ 14

6. WELDING C-STEELS WITH UTS > 490 MPA.................................. 19

7. RUN OUT LENGTH/VELOCITY OF FINE GRAINED STEELS......... 25

8. WELDING GUIDELINES FOR INSERT PLATES.............................. 28

9. WELDING LOW ALLOY CHROME MOLYBDENUM STEELS.......... 31

10. PRE-HEAT AND POST WELD HEAT TREATMENT ........................ 38

11. WELDING OF LOW ALLOY NICKEL STEELS ................................. 41

12. WELDING OF AUSTENITIC STAINLESS STEELS.......................... 44

13. WELDING OF SUPER AUSTENITIC STAINLESS STEELS............. 49

14. WELDING OF DUPLEX AND SUPER DUPLEX STAINLESS STEELS.5

15. WELDING OF MARTENSITIC STAINLESS STEELS ....................... 56

16. WELDING OF NICKEL ALLOYS....................................................... 59

Inhoudelijk beheer: CEI/6 Pagina: 1 van 91 Filenaam: 04002030.doc Rev.: A

Eigenaar: Voorzitter BBS proces 04 Niveau: 2


17. WELDING OF DISSIMILAR METALS ............................................... 64

18. WELDMENTS OF CLAD MATERIALS.............................................. 67

19. WELDING OF ALUMINIUM AND ITS ALLOYS................................. 71

20. WELDING OF COPPER AND COPPER ALLOYS............................ 74

21. WELDING OF TITANIUM, TANTALUM AND ZIRCONIUM............... 77

22. HARDFACING................................................................................... 79

23. CAST IRON....................................................................................... 84

24. GENERAL REQUIREMENTS FOR REPAIR WELDING................... 85

25. PREFERRED WELDING CONSUMABLES SHELL MOERDIJK AND SHELL PERNIS................................................................................. 90






1. ACTIVITEITENBESCHRIJVING In this document a background information/rules is given for the best practices of welding, experience gained from the past. It is a supplement for DEP 30.10.60.18 GEN Welding of metals, in which this part is deleted. In BBS doc 04.00.4052 Amendment to DEP-Gen requirements and reference are given to this doc.

2. REFERENTIE API 582 Welding Guidelines for the Chemical, Oil and Gas Industries DEP 30.10.60.18-Gen Welding of Metals Amendment to API 582 BBS doc. 04.00.4052 Amendments to DEP 30.10.60.18-Gen EN ISO 3834 Quality requirements for fusion welding of metallic materials

3. BEST WELDING PRACTICES GENERAL The Best Welding Practices are deleted from the Welding of Metals DEP 30.10.60.18-Gen. Shell Global Solutions International has collected these Best Practices separately but not published. SNC/SNC have these Best Welding Practices written down in this BBS document. Practical guidelines and requirements are given for the welding of:

Welding Quality. Carbon steel. Run out length/velocity of fine grained steels. Welding guidelines for Insert Plates. Low alloy steel (Mn, Mo, Ni etc.). Pre-heat and Post Weld Heat Treatment temperatures by welding. Stainless steels ((super-)Austenitic, Martensitic, (super-) duplex stainless steel). Nickel alloys (Inconel, Hastelloy etc.). SS cladding on carbon steel. Dissimilar materials. Aluminium (all applicable series). Copper (and copper alloys). Titanium, Tantalum and Zirconium. Repair welding Cast Iron. General requirements for Repair Welding. Hard facing. Preferred welding consumable brands SNR/SNC-Pernis and SNC-Moerdijk. Both metallurgical and practical aspects of welding are discussed as well as the different applicable types of welding and the use of shielding gasses.


4. WELDING QUALITY

Shell International Oil Products Best Welding Practice and Procedures

4.1 INTRODUCTION Welding is considered to be a special process because the final result cannot always be entirely verified. The quality of the weld has to be manufactured into the product, not inspected. This means that welding requires continuous control and/or documented procedures to follow. Based on these circumstances the standard series EN ISO 3834 concerning quality requirements in welding has been prepared. Equivalent systems are described in the various Codes that may be used for manufacturing conform to this BWP. EN ISO 3834 is intended for arc welding of metallic materials and it is independent of products. However, the principles and many of the detailed requirements are relevant also for other welding processes, as well as welding related processes. The implementation of EN ISO 3834 may also coincide with new or revised requirements in product standards (codes etc. for welded structures and products), or more stringent requirements as regards welding procedure testing, approval testing of welders, etc. as possibly described in DEP 30.10.60.18. In all cases the latter document (DEP) is leading.

Use of a standard for quality The use of a standard for control of weld quality is voluntary. It does not matter whether the standard is harmonised by a directive or enforced by any other control mechanism or not. It is just a solid basis for an organisation that in principle should be considered capable of fulfilling the requirements as set forth in DEP 30.10.60.18 and is therefore highly recommended. Sometimes it might be necessary for other reasons to follow a recognized standard (like ISO 3834), e.g. where the law on product reliability is anticipating that welding is performed properly. The EN ISO 3834 has been prepared to cover:

Independency of the type of construction manufactured. Quality requirements for welding in workshops and/or site. Guidance for describing a manufacturers capability to produce constructions to meet specified

requirements.

EN ISO 3834 contains many attributes that contribute to a full quality management system (QMS). This section identifies those QMS elements that the manufacturer should consider implementing to support the manufacturer's EN ISO 3834 quality requirements: 1. Control of documents and records. 2. Management responsibilities and organisational structure. 3. Provision of resources. 4. Training, assessment and qualification of operational personnel. 5. Assessment and qualification of processes. 6. Determination of requirements related to the product. 7. Review of requirements related to the product. 8. Planning of product realization. 9. Subcontracting, purchasing. 10. Monitoring and measurement of product. 11. Control of non-conforming product. 12. Corrective and preventive action. 13. Internal audit. 14. Customer property.




If there is any need to use one specific standard for a certain contract, this shall be stated so by the principal in the contract.

4.2 QUALITY OF WELDS A welded joint must possess those qualities which are necessary to enable it to perform its expected function in service. The joint must have the required physical and mechanical properties. It may need to have a certain microstructure and chemical composition to meet the minimum requirements. Welded joints by their nature contain discontinuities of various types and sizes. Below some pre-determined acceptable level, these are not considered harmful. The acceptance levels are specified in design codes like ASME VIII div. 1 or div. 2, EN 13445 for pressure vessels and ASME B31.3, B31.4, B31.8 for piping systems. These standards may refer to supporting standards where the levels may be detailed such as ISO 5817 and ISO 10042.

Control of welding production quality In order to ensure repeatable quality to be achieved in welding operations, all standards require welding procedure specifications (WPS) to be used for all welding activities. An example of such a WPS achieved through the application of WPSelect (see DEP 30.10.60.18 of June 2003), covering all reasonable requirements of any Code is attached to this document.

Type of defects/imperfections In general, imperfections may occur in welding. Depending on the welding process, position, condition, welders skill and the required weld quality, one or more of the following weld imperfections may be present in variable quantities: 1. Porosity. 2. Slag inclusions. 3. Lack of fusion. 4. Lack of penetration. 5. Cracks. 6. Undercut. 7. Oxide inclusions. 8. Heavy metal inclusions. 9. Shrinkage cavities.

A number of the welding defects mentioned above are more or less typical for specific welding processes.

Welding defects Characteristic for welding process(es)

Porosity SMAW, GMAW, GTAW, SAW, FCAW Slag particles SMAW, FCAW, SAW Lack of Fusion All welding processes Lack of Penetration All welding processes without backing strip Cracks All welding processes Undercut All processes used in position Oxide inclusions GTAW of aluminium Heavy metal inclusions GTAW Shrinkage cavities All welding processes

Defects in welds may originate from a number of different causes. No corrective steps can be taken unless the actual cause is known. It must, however, be kept in mind that in practice several factors may contribute simultaneously as sources of welding defects. To enable the user to deduce the underlying causes, a listing of possible defect causes is given.




Porosity

SMAW GMAW GTAW

Arc too long Insufficient gas flow Arc too long Root gap to wide Excessive gas flow Diameter gas cup too small Moist electrodes Deposit built up in nozzle Leaking gas tubes Wind, rain Wind, rain, draught Wind, rain, draught Dirt, rust, grease, paint etc. Dirt, rust, grease, paint etc. Dirt, rust, grease, paint etc Amperage too low Wire stick out too long Wrong manipulation Wrong polarity Wrong gas composition Too much shielding gas Travel speed too high Wrong parameters Too less shielding gas Insufficient degree of filling of the

welding wire.

Diameter gas cup too small Leaking gas tubes

Slag inclusions

SMAW, SAW, FCAW

Arc too short Current too low/high Root bead to convex Wrong electrode position Weaving too wide and too fast Wrong electrode diameter Improper cleaning between beads

Incomplete penetration

SMAW, GMAW, GTAW

Root gap too small Current too low Electrode too high up in the weld prep Electrode diameter too large Back chipping or gouging insufficient High-Low effect Wrong weld preparation Welding speed too high Wrong torch/gun/electrode position

Lack of fusion

SMAW GMAW GTAW Arc too long Low voltage/amperage Amperage too low Current too low Worn contact tube Travel speed too high Travel speed too high Wire extension too long Wrong torch manipulation Electrode manipulation Wrong gun manipulation Travel speed too high




Undercut

SMAW, GMAW, GTAW

Amperage/voltage too high Travelling speed too high Wrong electrode manipulation Too large electrode diameter

Heavy Metal Inclusions

GTAW

Amperage too high Wrong polarity Electrode diameter too small Stick out too long Wrong electrode material Strike starting

Cracks

SMAW, GMAW, GTAW

Root bead too thin Insufficient weld pre-heat Wrong welding procedure Wrong design Metal pick up Wrong welding parameters Chemical composition Wrong electrode coating Insufficient filling of end-crater

4.3 HEALTH RELATED TOPICS When welding, both the welder and its environment are exposed to a variety of fumes and gases related to the welding process. In most countries there are rules that may limit the exposure of personnel to welding fumes and gases. Some countries however dont have any rules. It is important for mankind to realize what kind of problems may occur during welding and how to prevent physical contact with welding fumes and gases. The type of hazards can be subdivided into two main groups: Metal fumes and gases. Both groups are listed below.

4.3.1 Metal fumes Source; Abstracted from Internet: National Occupational Health and Safety Commission Australia.

Lead Potential lead exposure occurs during welding and cutting of any metal coated with lead or lead-based paint. Lead poisoning is rare in welders, but may occur in persons employed in operations such as cutting lead-painted steel in ship breaking and bridge demolition. Occupational lead poisoning, which in welders results from exposure to lead oxide fume, may affect the blood, gastro-intestinal tract and nervous system.




Cadmium Cadmium may be present as a coating on certain materials being welded. Cadmium oxide fume inhalation may cause acute irritation of the respiratory passages, bronchitis, chemical pneumonia or excessive fluid in the lung tissues (pulmonary oedema). There may be a latent period of several hours between exposure and onset of symptoms. The effects of overexposure to cadmium fumes may resemble metal fume fever initially. A single exposure to a very high concentration of cadmium oxide fume may be fatal. Chronic cadmium poisoning results in injury to lungs and kidneys.

Manganese Potential exposure to manganese occurs whenever this metal is used in electrode cores and coatings or in electrode wire. Acute poisoning from oxides of manganese is very rare in welding, although respiratory tract irritation from the fume may occur. Exposure to fume from welding on manganese steel may give rise to acute inflammation of the lungs. Metal fume fever is also a possibility after exposure to manganese fume. Chronic manganese poisoning, characterised by a severe disorder of the nerves system, has been reported in welders working in confined spaces on high-manganese steels.

Zinc Zinc may be present as a surface coating on steel products, that is, galvanised steel. Exposure to freshly formed zinc oxide fume may produce a brief acute self-limiting illness known as metal fume fever, zinc chills or brass founders ague. The symptoms, which resemble those of an acute attack of influenza, usually occur several hours after exposure to fume and usually with complete recovery within about 24 to 48 hours. Freshly formed oxide fume from several other metals has also been reported to cause metal fume fever. Leucocytes, a transient increase in white blood cell counts, is reported to be a common finding in metal fume fever, but is not known to be common among welders.

Iron Most welding involves ferrous materials. The most abundant constituent of ferrous alloy welding fume is iron oxide. Long, continued exposure to such welding fume may lead to the deposition of iron oxide particles in the lungs. When present in sufficient quantities, the deposition is demonstrable on chest X-ray films as numerous fine discrete opacities (nodulation and stripping) resembling silicosis. The technical name for this is siderosis and it is a benign form of pneumoconiosis. Siderosis tends to clear up when the exposure to metallic particles stops.

Molybdenum Molybdenum is found in some steel alloys. Molybdenum fumes may produce bronchial irritation and moderate fatty changes in the liver and kidneys.

Cobalt Cobalt is a component in some high-strength, high-temperature alloys. Inhalation of cobalt fumes can cause shortness of breath, coughing and pneumonitis. Hypersensitivity appears to be involved because lung changes occur at low incidence and are varied in intensity and time of onset. In most cases, the symptoms disappear after exposure ends.

Vanadium Vanadium may be present in some filler wires and special alloy steels. Exposure to oxide fume, especially pentoxide (V2O5), gives rise to severe irritation of the eyes, severe throat and respiratory tract irritation, and may also cause chemical pneumonia.

Nickel Nickel is a potentially carcinogenic metal found in fumes from the welding of nickel-plated mild steel, stainless steel, nickel base alloys and high-strength low-alloy steel electrodes. Nickel oxide has been found to be carcinogenic in laboratory animals. There is, however, very little direct information on the health effects of nickel-bearing welding fume on welders. Irritation of the respiratory tract has occurred in stainless steel welders.




Chromium Chromium may be present as a coating on the work piece, and mainly in stainless steel, hardfacing and chrome-alloy electrodes. Chromium is normally not present in any significant amount in aluminium alloys. Chromate, which may be generated in stainless steel welding fumes or in fumes from hardfacing and chrome-alloy electrodes, is an irritant to the mucosal tissue in the respiratory tract. Exposure to fume containing high concentrations of water-soluble chromium (VI) during the welding of stainless steel in confined spaces has been reported to result in both acute and chronic chrome intoxication, dermatitis and asthma. Epidemiological studies and animal tests have confirmed certain chromium (VI) compounds as occupational carcinogens. These health risks were determined from non-welding occupations. GMAW stainless steel welders are usually likely to be exposed to much smaller concentrations of chromium (VI) than MMAW stainless steel welders. A considerable amount of stainless steel welding is carried out nowadays using GMAW and GTAW methods. Chromium (III) compounds are generally believed to be biologically inert. Welding fumes may contain Cr2O3 (a chromium (III) compound), or double oxides, such as FeO Cr2O3, or both.

Silica and silicates The silica and silicates formed in welding fumes are amorphous, that is, not crystalline, and are generally believed not to be harmful.

Fluorides Welders may be exposed to fluoride dust, fume and vapours from certain MMAW, FCAW and GMAW operations and SAW fluxes. Fluoride fumes may produce irritation of the eyes, throat, respiratory tract and skin. Chronic fluorosis is a syndrome characterised by an increased density of bones and ligaments due to fluoride deposition. However, no corroborating data are available which identify a relationship between exposure to fluoride-containing welding fumes and disorders of bones or ligaments.

Other metals Welding may produce fume from other metals, including aluminium, copper, magnesium, tin, titanium and tungsten. Within the confines of the current information available, no serious health disorders in welders are known to occur from exposure to fume from these metals but, under certain conditions, copper, aluminium and magnesium may give rise to metal fume fever and others to irritation of the respiratory tract. Beryllium is a volatile and toxic component that may be present in many copper alloys being welded, that is, in the work piece itself. Beryllium oxide fume is very toxic to the respiratory tract, lungs and skin, and is quick-acting. Beryllium is a suspect human carcinogen. Note that beryllium may also be present in some aluminium or magnesium brazing alloys.

4.3.1.1 Preventive measures In all cases the best action to prevent long term exposure to the up mentioned metal fumes, is the use of local fume extraction, together with additional ventilation.

Local rules may give stringent action to be taken!




4.4 GASES

Oxides of nitrogen The oxides of nitrogen, nitric oxide and nitrogen dioxide, are frequently formed by the direct combination of oxygen and nitrogen in the air surrounding the arc or flame, as a result of heat from the electric arc or gas torch (oxidising flames) during welding and cutting. In outdoor or open shop welding, hazardous abnormal concentrations are unlikely, except perhaps for short periods. In confined spaces, hazardous concentrations of nitrogen oxides may rapidly build up in welding operations. High concentrations of nitrogen oxides have also been found during plasma-arc cutting of stainless steel. Exposure to oxides of nitrogen may not always produce immediate effects but may result in fatal excessive fluid in the lung tissues (pulmonary oedema) some hours after the exposure stops.

Ozone Ozone is formed only in small amounts in SMAW and in gas welding. It is, however, produced in significant amounts in GTAW, GMAW when welding with argon, especially when high amperages are used. High ozone concentrations are especially a problem when welding on reflective surfaces, such as aluminium and its alloys and stainless steel, and with high-energy processes such as plasma arc welding. Ozone is actually formed a short distance away from the arc. The persistence of ozone under certain conditions may be explained as an inverse function of the amount of fume produced. The greater the mass of fume (particulate), the less the penetration by ultraviolet radiation and thus the less ozone produced by the ultraviolet radiation acting on oxygen. Ozone also reabsorbs ultraviolet radiation of wavelengths of 200 to 290 nm and can spontaneously decompose back to oxygen. Harmful levels of ozone may be found in welding in confined spaces. The gas is very irritant to the upper respiratory tract and lungs and its effects may be delayed. Ozone is capable of reacting explosively with combustible materials.

Carbon monoxide Carbon monoxide is derived from carbon dioxide-shielding atmospheres by reduction of shielding gas, and to a much lesser extent in all welding of steel by partial oxidation of carbon in the consumables. Carbon monoxide will also be produced in gas welding when combustion of acetylene is incomplete, as with a reducing flame. Carbon monoxide levels may build up in confined spaces and poorly ventilated spaces. Over exposure may cause drowsiness, headache and nausea. If carbon monoxide exposure is sufficiently severe, unconsciousness may occur.

Carbon dioxide Carbon dioxide at high concentrations can act as an asphyxiant. It is therefore necessary in GMAW in confined spaces to maintain adequate air and oxygen to avoid asphyxiation of the welder. Note that high oxygen concentrations should also be avoided since they constitute a fire hazard.

Phosgene The toxic gas phosgene, also known as carbonyl chloride, is not a normal component of welding gases, but is formed by the oxidation of chlorinated hydrocarbons (for example, trichloroethylene, trichloroethane and perchloroethylene), such as when welding is carried out in the presence of solvent vapours escaping from a nearby degreasing tank or when solvent is left behind after degreasing. Exposure to phosgene produces, after a latent period of several hours, irritation of the respiratory tract or perhaps serious lung damage. Phosgene formation is promoted by ultraviolet radiation, hot metal surfaces, flame and cigarette smoking. The gas-shielded arc welding processes (GMAW and GTAW) and plasma processes provide greater ultraviolet light intensity than the flux-shielded arc welding processes (MMAW, SAW, FCAW). Note also that heat and ultraviolet radiation from the welding arc may react with solvent vapour to produce irritant gases such as acetylchloride and acetylchloride derivatives such as dichloroacetylchloride.

Phosphine Phosphine is generated when steel coated with a rust proofing compound is welded. High concentrations of phosphine gas are irritating to the eyes, nose and skin. There may also be serious effects on the lungs and other organs.




Insufficient oxygen In GMAW, the presence of inert gases (argon, helium) in confined work environments may reduce the oxygen content of the atmosphere to dangerous levels, with the threat of asphyxiation. See also the section on carbon dioxide in this appendix.

Pyrolytic products of resins used in primers/paints The main products of thermal decomposition of resins used in primers and paints are carbon monoxide and carbon dioxide. Specific toxic or irritant chemicals given off from the resins used in priming materials include such hazardous substances as phenol, formaldehyde, acrolein, isocyanides and hydrogen cyanide. Usually, a very complex mixture of organic gases is formed.

4.4.1 Preventive measures In all cases the best action to prevent long term exposure to the up mentioned metal fumes, is the use of local fume extraction, together with additional ventilation.

Local rules may give stringent action to be taken!

Note: Fume particles may be filtered adequately; gases however can never be filtered!




Example of first page of a WPS




Example of the second page of a WPS




5. WELDING OF CARBON STEELS WITH UTS < 490 MPA

Shell Global Solutions Best Welding Practice and Procedures

5.1 INTRODUCTION Carbon steel with an UTS < 490 MPa is an iron alloy, containing carbon (C < 0,25%), manganese (Mn < 0,8%) and silicon (Si < 0,5%). It belongs to the group of unalloyed steels; this group may also contain up to 0,5% Mo. These materials belong to the following groups:

According ASME: P1 and P3. According EN ISO 15608: Group 1, 2, 3 and 11. An increase of the carbon content will lead to higher UTS and yield strengths and lower elongations. For steels, having an UTS < 490 MPa, the yield strength is < 320 MPa and the elongation about 20 24%. These steels are mostly delivered in the normalised condition (N), that means that after rolling a heat treatment (normalising) has been carried out. These steels are generally used for construction material for pressure vessels, piping, supports and building structures. The readily weldable low-carbon steels are applied for most cases. The weldability of ferritic steels depends on the carbon content and the carbon equivalent (Ceq). The carbon content can be calculated according the IIW-formula:

Ceq. = % C + % Mn/6 + % (Cr + Mo + V)/5 + % ( Ni + Cu)/15

Good weldability, without the need of PWHT is obtained when the following product analyses are met:

C 0,23 % for plate material. C 0,25 % for forgings and castings. Ceq < 0,45 %.

5.2 WELDABILITY The weldability is directly related to the carbon content and Ceq. If the values are beyond the above limits, more precautions shall be taken. The main problems are hardening in the weld metal and HAZ, with a high risk of hydrogen cold cracking. If the specifications for the carbon content and Ceq are not met, a PWHT may be required to comply with the design code. Generally no special precautions are required for welding. Suitable welding electrodes are of the rutile, cellulose or basic low-hydrogen types. For wall thicknesses above 25 mm, basic low hydrogen electrodes shall be applied.

5.3 APPLICABLE WELDING PROCESSES These steels may be welded with one or more of the following welding processes (see API 582 clause 5):

SMAW GMAW FCAW GTAW SAW FCAW-S OFW




5.3.1 Welding consumables

5.3.1.1 SMAW (ISO process number 111) According to API 582 Appendix A table A1, the electrodes to be used shall be of the type:

E70XX low hydrogen (according to AWS A 5.1) or E 42 X B XX H4 (according EN 499) The hydrogen content of the weld deposit shall be 10 ml/100 g maximum.

For rootpassing electrodes type

E6010 (according tot AWS 5.1) or E 42 X C XX (according to EN 499) may be used. For references see: API 582 Appendix A table A-1 and DEP 30.10.60.18 clause 6.1 and 6.6.

The use of dried basic electrodes is preferred when:

Thick materials have to be welded (wall thickness above 25 mm). Welding at temperatures below + 5C (see DEP 30.10.60.18 clause 8.3: welding conditions). The materials are critical to porosity, e.g as found in good machinable steels.

5.3.1.2 GMAW with solid wire (ISO process number 135) Welding with solid wire is allowed. For solid wires, all types according to

AWS 5.18: ER 70S-6 EN 440: G 46 4 M G3 Si1 may be used.

The filler wires used shall be compatible with the type of gas. De-oxidizing elements shall be present in the filler wire. Only for welding structural steels CO2 can be used. Disadvantages are a globular metal transfer and weld spatter (metal losses about 15%). Other suitable gasses are Argon with additions of CO2 like i.e. 80% Ar 20% CO2 and 85 Ar 15 CO2. These gasses maintain a stable arc and give little spatter. The latter mixture is recommended when deeper penetration is required (e.g. for welding thicker plates). The purity of the shielding gasses used and its flow shall be stated on the WPS.

For references see: DEP 30.10.60.18 clause 6.1 and 6.6.

5.3.1.3 FCAW (ISO process number 136) For flux-cored arc welding, basic-, rutile as well metal-cored wires may be used. The deposit shall have a maximum hydrogen content of 10 ml/100 g weld metal. Classification according to:

AWS 5.20: E 7X T-X EN 758: T 46 R/B/M XX The flux cored wires to be used shall be compatible with the type of shielding gas. The purity of the shielding gasses used and its flow shall be stated on the WPS.

For references see: DEP 30.10.60.18 clause 6.1, 6.6 and 7.6.




5.3.1.4 GTAW-welding (ISO process number 141) For root-passing the GTAW-process may be used, applying the type of wire as shown below. Classification according:

AWS 5.18: ER 70 S-6 EN 1668: W 42 5 W2 Si There shall be no oxidizing element as oxygen in the shielding gas; such to avoid oxidation of the tungsten electrode. When welding the root and the first pass, the backside of the weld can be protected to prevent oxidation. When welding unalloyed carbon-manganese steels the backing gas may be N2 or Ar (99,99%).

5.3.1.5 SAW (ISO process number 121) The SAW-process may be used using solid or flux-cored wires. The type of welding flux to be used depends on the application and shall be compatible with the welding wire:

Welding thick plates (< 20 mm) basic fluxes shall be used (aluminate-basic or fluoride-basic). Welding fillet welds rutile fluxes may be used. The consumables shall be of the low-hydrogen type, that means that the hydrogen contents of the deposited weld metal shall be below 10 ml/100 g. Recycling of the welding flux is permitted only when it can be stated as conditioned recycling.

For references see: API 582 clause 6.1 and DEP 30.10.60.18 clause 6.1and 6.6.

5.3.1.6 FCAW-S (ISO process number 114) With respect to API 582 clause 5.2.4 the self shielded flux cored arc welding process may be used, for welding carbon steel structural items only. The welding wire types identified by the manufacturer for multipass application should be used.

For references see: API 582 clause 6.1.

5.3.1.7 OFW (ISO process number 311) With reference to DEP 30.10.60.18 clause 5.2 this process may only be used for pipe welding, if all of the following requirements are met:

The base material has an UTS < 460 Mpa. Service temperature is above +10C. Pipe diameter < 50 mm. Wall thickness < 5 mm.

5.4 WELD PREPARATION Flame cutting, plasma cutting as well as cold shearing may be used for weld preparation. Cold shearing may be applied up to 25 mm material thickness. For the demands for the weld preparation see DEP 30.10.60.18 clause 8. To prevent excessive carbon pick-up during arc-air gouging, a power source with a minimum open circuit Voltage over 80 V shall be used. In addition, the pressure and the amount of compressed air must be in accordance with the recommendations of the electrode manufacturer. When gouging has been carried out, the edges shall be dressed back for at least 2 mm by grinding or machining to eliminate the zone with carbon pick up. Also after cold shearing the edges shall be dressed back for 2 mm., unless the pate thickness is less than 10 mm.

For references see: DEP 30.10.60.18 clause 8.




5.5 WELDING TECHNIQUE

SMAW Welding can be carried out using the stringer bead method as well using the weaving method; the latter with the restriction of the maximum weaving-width of 3x diameter of the core wire.

GMAW GMAW can be used in both the short circuiting and the spray-transfer mode. When welding plate thicknesses over 10 mm the short circuiting mode is prohibited.

Pre-heating Pre-heating of these types of steels is hardly necessary. Pre-heating shall be done when welding:

thick materials (> 20 mm). at ambient temperatures below + 5C. Minimum pre-heat requirements shall follow the applicable code, such as ASME Section VIII and others as specified in API 582, clause 8.1. If EN 1011 is used, the pre-heat temperature may be calculated based on the wall thickness, the heat-input, the hydrogen content of the consumable to be used and the thermal efficiency of the welding process. Requirements for the application of the pre-heating are given in APT 582 clause 8.2 and DEP 30.10.60.18 clause 8.1.

Heat-input The heat input range shall be specified in the WPS, so the maximum hardness in the base material, heat affected zone and weld metal shall not exceed:

248 HV10 for steels in process service. 325 HV10 for structural steels. For references see: DEP 30.10.60.18 clause 12.6.1.3

Interpass temperature The interpass temperature is the maximum temperature the material may have the moment the arc passes this spot. The maximum interpass temperature shall be specified in the WPS when impact testing is required. This maximum temperature for these types of steel is 315C. See API 582 clause 8.3 and 8.4.

Bead shape These materials can be welded with stringer beads as well as using the weaving technique. For optimum mechanical properties only stringer beads with a maximum thickness of max. 4 mm shall be used. In DEP 30.10.60.18 clause 8 more information (e.g. weld fit-up, the use of backing materials a.s.o) is given. In API 582 clause 5.2.2 and 5.2.3 restrictions are given for using the GMAW-S process (short circuiting gas metal arc welding) as well as for the GMAW-P-welding (pulsed gas metal arc welding).

5.6 WELDING PLATES When welding plates, common practice should be used. For weld fit-up, the use of backing, welding conditions, weld application and so on: see DEP 30.10.60.18 clause 8.1. Pre-heating should be used when welding plates with a wall thickness > 20 mm and at ambient temperatures below + 10C.





5.7 WELDING PIPES The OFW may be used for welding pipes when:

Service temperature is above 0C Pipe diameter DN 50 mm Wall thickness < 5 mm. For root passing the GTAW process may be used for piping with a diameter equal or less than DN 80. Cellulose type coated electrodes may be used for the root pass and the second pass of single groove welds in pipes with diameter > 8, regardless to base material thickness.

For references see: API 582 clause 6.1.1 DEP 30.10.60.18 clause 5.2.7 and 5.2.8.

5.8 POST WELD HEAT TREATMENT After welding, no heat treatment is needed. Any heat treatment shall be specified on the WPS.

For references see: API 582 clause 9 DEP 30.10.60.18 clause 9.1

For decreasing the hydrogen content after welding, a soaking treatment shall be done for 2 hrs at 200C, without cooling down to ambient temperature directly after welding. For post heat treatment and holding times: see DEP 30.10.60.18 clause 13.2. Depending the amount of weld metal, the welding-sequence, the wall thicknesses and the application, stress relieving may be considered, if not specified by the design code.

5.9 REPAIR WELDING For repair welding, the processes mentioned in clause 4 of this document shall be used, except the SAW-process for the applications as mentioned in DEP 30.10.60.18 clause 5.2.6.3. For repair welding all demands for welding these types of steel as stated in this document shall be applied, in conjunction with the requirements as given in Shell Best Welding Practice and Procedures: General requirements for repair welding.

5.10 REFERENCES API 582, edition march 2001. Design and engineering practice DEP 30.10.60.18, edition June 2003.




6. WELDING C-STEELS WITH UTS > 490 MPA


6.1 INTRODUCTION Within the group of steels with an UTS > 490 MPa there are two possibilities:

Steels having a carbon content > 0,25%; they are supplied in the so called Normalized condition, that means that after rolling a heat treatment has been carried out to get the desired strength.

Steels having a carbon content < 0,20% with small additions of other alloying elements, such as Cr, Mo, N2, Ni, V. These elements make it possible to get the desired strength after a heat treatment in combination with the rolling process. These type of steels belong to the group so called fine-grained steels. Other names for these type of steels:

AC-steels (accelerated cooled steels) QT-steels (quenched and tempered steels) and TM-steels (themo-mechanically treated steels).

These materials belong to the following groups:

According to ASME: P1 and P3. According to EN ISO 15608 Group 1, 2 and 11. These steels are generally used for construction material for pressure vessels, piping, supports and building structures. The weldability of ferritic steels depends on the carbon content, the carbon equivalent (Ceq) and the thermal history. The carbon content can be calculated according the IIW-formula:

Ceq. = % C + % Mn/6 + % (Cr + Mo + V)/5 + % ( Ni + Cu)/15

Good weldability, without the need of PWHT is obtained when the following product analyses are met:

C 0,23% for plate material. Ti + Nb 0,15%, each element not being over 0,05%. C 0,25% for forgings and castings. Ceq < 0,45%. The weld quality is directly related to the carbon content and Ceq. If the values are beyond the above limits, more precautions shall be taken. The main problems are hardening in the weld metal and HAZ, with a high risk of hydrogen cold cracking. If the specifications for the carbon content and Ceq are not met, a PWHT may be required to comply with the design code.

6.2 WELDABILITY

Normalized steels In most cases these normalized steels do not meet the above mentioned C and the Ceq requirements, and approval by the principal is required. If they are considered acceptable by the principal, special precautions shall be taken to avoid unacceptable hardening and cold cracking. Basic low-hydrogen welding consumables shall be used and pre-heating shall be performed in accordance with the applicable design code. Non- matching consumables may cause hydrogen cracking under corrosive conditions , e.g. water with H2S, HF, etc. For more information see clause 6 of this BWP.




Fine grain steels On the other hand, the chemical composition of the AC-steels is tuned in such a way that after rapid cooling, immediately after rolling, the structure consists of fine grains. The TM-steels also have a slightly different chemistry in respect to the AC-steels, to make it possible to get fine grains after a rolling sequence at a lower temperature as common practice. Due to the low carbon content, resulting in a low carbon equivalent, hardening of HAZ Is not likely to occur, even when welding with a low heat-input. As these steels have their strength caused by the existence of fine grains, due to the thermal history, excessive growth of the grains must be prevented. So welding with a limited heat input shall be carried out. See clause 6: Welding technique. For the fine grain steels with an UTS > 490 MPa precautions are required to avoid hydrogen cold cracking and hardening. Basic low-hydrogen electrodes shall be used. Pre-heating between 100 and 150C in accordance with the design code shall be performed for wall thicknesses above 25 mm. Fine grained steels have improved impact properties.

6.3 APPLICABLE WELDING PROCESSES These steels can be welded with one of the following welding processes (see API 582 clause 5):

SMAW GMAW FCAW GTAW SAW FCAW-S When repair welding pressure vessels, storage tanks or pipeline, the SAW-proces shall not be used. (DEP 30.10.60.18 clause 5.2.6.3).

6.3.1 Welding consumables

6.3.1.1 SMAW (ISO process number 111) According to API 582, appendix A-table A.1, the electrodes to be used shall have a basic coating (type E7016 or E7018, according AWS SFA 5.1, and E 46 X B XX H5 according EN 499) However, for high strength steels, the tensile strength of electrodes to be used shall, at least be equal or higher than the UTS of the steel itself. So electrodes of the types E80XX, E 90XX, and with even higher classification according to AWS SFA 5.5 or E 55XB H5 according EN 757 should be used. All the electrodes shall have a low hydrogen content, that means that the hydrogen content of the deposit shall not exceed 10 ml/100 g deposit. When not delivered and stored in the standard vacuum packages, the electrodes shall be re-backed according the prescriptions of the supplier.

6.3.1.2 GMAW with solid wires (ISO process number 131) The strength of the weld deposit, being the result of a combination of the wire and the shielding gas, shall at least meet the strength of the base material to be welded. So wires, meeting the AWS SFA 5.28 classifications ER 80S, ER 90S and even higher classifications, shall be used when welding higher strength steels. The filler wires used should be compatible with the type of gas. In case of active gasses like CO2, de-oxidizing elements shall be present in the filler wire. For welding these materials, only gas mixtures shall be used. Disadvantages are a globular metal transfer and weld spatter (metal losses about 15%). Other suitable gasses are Ar with additions of CO2 like i.e. 80% argon 20% CO2 and 85 Ar 15 CO2). These gasses maintain a stable arc and give little spatter. The latter mixture is recommended when deeper penetration is required (e.g. thicker plate).




The purity of the shielding gasses used and its flow shall be stated on the WPS.

For references see: DEP 30.10.60.18 page 6 clause 6.1 and 6.6.

6.3.1.3 Flux cored wires (ISO proces number 136) Welding with flux cored wires can be done with either rutile, basic or metal cored wires. The strength of the weld deposit, being the result of a combination of the wire and the shielding gas, shall at least meet the strength of the base material to be welded. So wires, meeting the AWS SFA 5.29 classifications E 8XT, E 9XT and even higher classifications, shall be used when welding higher strength steels. As already stated: the chemical composition of the wire shall be based upon the type of shielding gas to be used, resulting in the strength as desired For welding pressure containing equipment, the diffusible hydrogen limit for FCAW electrodes (as manufactured) shall be capable of meeting the specification as shown below: Where the specified minimum tensile strength for the electrode is 70 ksi (483 MPa) (per AWS SFA 5.29), the maximum diffusible hydrogen designation for the electrode shall be H4.

Note: When welding with 70 ksi (438 MPa) electrodes to steels having a tensile strength of 80 ksi (522 MPa) or greater, H4 designated electrodes shall be used.

Comparable: T 42 X B/C/M XX H5 according to EN 758.

6.3.1.4 TIG-welding (ISO process number 141) For root-passing the TIG-process may be used, using the type of wire matching the desired tensile strength. AWS 5.2: ER 80 S-G, ER 90-G or with even higher classifications

There shall be no oxidizing element as oxygen in the shielding gas used; such to avoid oxidation of the tungsten electrode. When welding the root and the first pass, the reverse side of the weld may be protected to prevent oxidation. When welding un alloyed carbon-manganese steels the backing gas may be N2 or Ar (99,99%).

6.3.1.5 SAW (ISO process number 121) The SAW-process may be used, using solid or flux-cored wires. Due to the mechanical properties of these type of steels, only basic welding fluxes shall be used. The welding fluxes shall give a weld metal deposit with a diffusible hydrogen content, which shall not exceed 10 ml/100 g weld metal. (See DEP 30.10.60.18 clause 6.6). The fluxes shall be stored in a dry place and be re-backed, according the prescription of the manufacturer.

6.3.1.6 FCAW-S (ISO proces number 114) With respect to API 582 clause 5.2.4 the self shielded flux cored arc welding process may be used, for welding carbon steel structural items only. The welding wire types identified by the manufacturer for multipass application should be used.

For references see: API 582 clause 6.1.

6.4 WELD PREPARATION Flame cutting, plasma cutting as well as cold shearing may be used for weld preparation Cold shearing may be applied up to 25 mm material thickness. When thermal cutting or arc-air gouging the normalised types, pre-heating shall be considered to prevent hardening. To prevent excessive carbon pick-up during arc-air gouging, a power source with a minimum open voltage over 80 V shall be used. Besides, the pressure and the amount of compressed air shall be in accordance with the recommendations of the supplier.




When gouging has been carried out, the edges shall be dressed back for a minimum of 2 mm by grinding or machining, to eliminate the zone with carbon pick up. Also after cold shearing the edges shall be dressed back for 2 mm, unless the pate thickness is less than 10 mm.



General SMAW can be carried out in the stringer bead technique or the weaving technique, the latter with maximum weaving width of 3x the diameter of the core wire. GMAW can be used in both the short circuiting and the spray-transfer mode. When welding plate thicknesses over 10 mm the short circuiting mode is prohibited.

6.5.1 Normalized steels When welding these type of steels (basic) low hydrogen consumables shall be used (see DEP 30.10.60.18 clause 6.6).

Pre-heating Pre-heating of these types of steels is necessary to prevent hardening of the HAZ. Minimum pre-heat requirements shall follow the applicable code, such as ASME Section VIII and others as specified in API 582, clause 8.1 According to EN 1011 it is possible to calculate the pre-heat temperature on basis of the wall thickness, the heat-input, the hydrogen content of the consumable to be used and the thermal efficiency of the welding process. Requirements for the application of the pre-heating are given in APT 582 clause 8.2 and DEP 30.10.60.18 clause 8.

Welding techniques All normal welding techniques can be used, from weaving till stringer beads. For optimum mechanical properties, welding with stringer beads shall carried out. If closing of the gap cannot be done in the middle of the weld but next to the base material, the use of the temperbead technique shall be considered.

a

322 274

270

270 274

262

270

376206

HAZ

Basematerial

Tempered HAZ

The effect of tempering

'Temperbead technique'

Vickers micro-hardness

Tempered HAZ




Heat-input Special attention shall be payed to the heat-input. The heat input range shall be specified in the WPS, so the maximum hardness in the base material, heat affected zone and weld metal shall not exceed:

248 HV10 for steels in process service. 325 HV10 for structural steels. For references see: DEP 30.10.60.18 clause 12.6.1.3.

Interpass temperature The interpass temperature is the maximum temperature the material may have the moment the arc passes this spot. The maximum interpass temperature shall be specified in the WPS when impact testing is required. This maximum temperature for these types of steel is 315C. See: API 582 clause 8.3 and 8.4.

6.5.2 Fine grain steels Fine grained steels have improved impact properties. When welding these type of steels (basic) low hydrogen consumables shall be used (see DEP 30.10.60.18 clause 6.6).

Pre-heating In general, for the lower strength steels, pre-heating is hardly necessary, when low hydrogen consumables, having a deposit of which the hydrogen content does not exceed 10 ml/100 g deposit, are used. For the higher strength steels precautions are required to avoid hydrogen cold cracking and hardening. Basic low hydrogen electrodes shall be used. Pre-heating between 100 and 150C in accordance with the design code shall be performed for wall thicknesses above 25 mm. Requirements for the application of the pre-heating are given in APT 582 clause 8.2 and DEP 30.10.60.18 clause 8.1 on page 8.

Welding techniques All normal welding techniques can be used, from weaving till stringer beads. The weaving technique with a maximum weaving width of 3 x the diameter of the core wire. For optimum mechanical properties, welding with stringer beads shall be done. If closing of the gap cannot be done in the middle of the weld but next to the base material, the use of the temperbead technique shall be considered.

Heat- input The heat input shall be specified in the WPS, so the maximum hardness in the base material, heat affected zone and weld metal shall not exceed:

248 HV10 for steels in process service 325 HV10 for structural steels For references see: DEP 30.10.60.18 clause 12.6.1.3

Interpass temperature The interpass temperature is the maximum temperature the material may have the moment the arc passes this spot. The maximum interpass temperature shall be specified in the WPS when impact testing is required. This maximum temperature for these types of steel is 315C. See: API 582 clause 8.3 and 8.4.

6.6 WELDING PLATES When welding plates common practice should be used. For weld fit-up, the use of backing, welding conditions, weld application and so on: see DEP 30.10.60.18 clause 8.1.




When root passing joints where high stresses can occur, i.e. great wall thicknesses, the use of low yield consumables can be considered. However, these consumables may only be used after agreement from the principal. For weld fit-up, the use of backings, welding conditions, weld application and so on: see DEP 30.10.60.18 clause 8.1. Pre-heating should be used when welding plates with a wall thickness > 20 mm and at ambient temperatures below + 10C. The weld shall be completed before the pre-heat temperature is lowered, if at least 50% of the weld has been completed. See DEP 30.10.60.18 clause 8.1

6.7 WELDING PIPES For welding pipes all the processes as mentioned in clause 4 may be used, except OFW. Besides, above pipe diameters of 4, the use of cellulosic electrodes can be considered as well for root passing as for the second pass, unless the strengths of the base material cannot be achieved. For root passing the GTAW process may be used for piping with a diameter equal or less than DN 80.

6.8 POST WELD HEAT TREATMENT After welding no heat treatment is needed. If a heat treatment has to be carried out it shall be specified on the WPS. For references see: API 582 clause 9

DEP 30.10.60.18 clause 9.1

For decreasing the hydrogen content after welding, soaking may be advisable for 2 hrs at 200C, without cooling down to ambient temperature directly after welding. For post heat holding times: see DEP 30.10.60.18 clause 13.2. Depending the amount of weld metal, the welding-sequence, the wall thicknesses and the application stress relieving, may be considered.

6.9 REPAIR WELDING For repair welding these types of steel, the processes, mentioned in clause 4 of this document, may be used, except the SAW-process for the applications as mentioned in DEP 30.10.60.18 clause 5.2.6.3. For repair welding all the requirements for welding these types of steel, as stated in this document, shall apply, in conjunction with the requirements as given in Shell Best Welding Practice and Procedures: General requirements for repair welding.





7. RUN OUT LENGTH/VELOCITY OF FINE GRAINED STEELS Fine grained steels have improved impact properties. Steels with guaranteed impact values below 20C (see DEP 30.10.02.31-Gen. Fine-grained steels are sometimes referred to as killed steel. In order to avoid the occurrence of grain growth or too high a hardness in the heat-affected-zone (risk of cold cracking) due to welding, fine grain steels must be welded with a wall thickness related heat input. The run-out length i.e. welding velocity determines the heat-input and subsequently the cooling time 800 500C (t 800 - 500). See also Figure 7-1 and Figure 7-2 for the relationship between heat input, plate thickness and t 800 - 500 for respectively fine grained steels with -and without pre-heat.

The t 800 - 500 is the determining factor for the grain size in the heat-affected-zone (satisfactory ductility in HAZ). For that reason the WPS, for this type of material, must contain the run-out-length (welding velocity) and the gross heat-input.




Figure 7-1: Relation between heat-input, plate thickness and t 800-500 for fine-grained steels without pre-heat.




Figure 7-2: Relation between heat-input, plate thickness and t 800 - 500 for fine-grained steels with pre-heat 100-150C.




8. WELDING GUIDELINES FOR INSERT PLATES The set in plates can be applied with the following guidelines:

Using a set in plate welding construction is regarded as complex welding. Therefore the required documentation for complex welding shall be made.

A set in plate is applied without a welding gap, with a minimum tip height of 2-3 mm. The corners of the plate have a minimum roundness of R=5t with a minimum of 50 mm. The

only exclusion is a set in plate near a long seem construction, then 90 corners are used at the weld side. This location has to be welded last. Crossings of weld seems have to be prevented where possible.

Welding the corners at the last stage of welding, to prevent cold cracking by shrinkage. Always welding toward the stopping place of the other weld; so not welding further from the

stopping place.

Always use internal supports to prevent deformation in circumferential direction. Plate in line Maintain welding sequence 1 to 8 (see Figure 8-1), only one electrode per run may be used. Start next run welding away from the stopping place of the last run towards the last run. Welding towards Corners must be welded at the end of the sequence. The arrow direction in the sketch is valid in the so-called 1G position only. If welding in the 3G position is needed only vertical-up welding is allowed.

Figure 8-1: Welding sequence for plate insert

Circular plate in line This method is also valid for oval shaped insert plates. Maintain welding sequence 1 to 8 for welding in the 1G position (see Figure 8-2). For welding in the 3G position maintain the same sequence, however only vertical-up welding is allowed.




Weld fit-up Weld configuration must be selected in such a way that a symmetrical weld configuration is achieved. The insert plates must be fitted into the wall in such a way that no gap is present. This requirement is not applicable for single side welds.

Figure 8-2: Weld sequence for circular plate insert




Insert plates in tanks




9. WELDING LOW ALLOY CHROME MOLYBDENUM STEELS 1 Cr thru 9 Cr, including modified versions.


9.1 INTRODUCTION Steels alloyed with molybdenum and chromium are designed for higher temperature application 550C; additionally, these steels have an improved creep-resistance and hot hydrogen resistance. Creep can be defined as the appearance of a permanent elongation, due to long-term stresses (far) below the yield strength. Creep can be propagated by elevated temperatures. Additions of molybdenum, chromium, vanadium, titanium and niobium increase the resistance to creep.

9.2 WELDABILITY First of all, with respect to the carbon-manganese construction steels, the carbon-equivalent will be higher. So pre-heating shall be applied to control excessive hardening of the HAZ. Secondly, the low alloy composition promotes the forming of martensite, and as the ability to deform this martensite is much less at ambient temperatures, due to the welding stresses, cracks will occur. Third, due to the chemical composition, precipitates will be formed at the grain boundaries. When stress relieving, these precipitates block the necessary deformation resulting from thermal stresses. As internal deformations cannot occur, cracking will result. This phenomena is known as reheat cracking. The vanadium-containing types of these steels are more sensitive to this phenomena. Fourth, temper embrittlement can occur. Temper embrittlement is defined as the brittleness that occurs when some alloyed steels are kept at certain temperatures (between 370 600C) for a certain time, or pass through this temperature area. This form of brittleness results in a change of the transition temperature up to 150C! This brittleness is a result of segregations, formed along the grain boundaries. Investigations have shown that there is a relation between the temper embrittlement and the amount of the elements Sb, As, Sn and P. To test the sensitivity to temper embrittlement, a special heat treatment has been developed. During this heat treatment, cooling down is performed in steps. This heat treatment is known as the step cool treatment. After this heat treatment the toughness is tested by Charpy-impact tests. See: API 934.

9.3 APPLICABLE WELDING PROCESSES For welding these chromium-molybdenum steels one of the following processes may be used:

SMAW GMAW GTAW SAW Except for repair welding of pressure vessel, storage tanks and pipelines, the SAW process shall not be used (see: DEP 30.10.60.18 dd. June 2003, clause 5.2.6).

9.4 WELDING CONSUMABLES

9.4.1 SMAW (ISO process number 111) For welding with the SMAW-process, only low hydrogen basic electrodes, having a deposited weld metal with a diffusible hydrogen content not exceeding 10 ml/100 g weld metal, shall be used. The chemical composition of the consumables shall at least comply with the chemical composition of the base material to be welded. All the alloying elements shall be present in the core wire; that means that the use of synthetic electrodes is prohibited. Synthetic electrodes contain (part of) the alloying elements in the covering.




For the classification of the consumables to be used see: API 582, table A1.

9.4.2 GMAW

9.4.2.1 Solid wire (ISO process number 131). When welding with solid wires, the chemical composition of the deposited weld metal shall, match the composition of the base material. The filler wires used should be compatible with the type of gas. In case of active gasses like CO2, de-oxidizing elements shall be present in the filler wire. For welding these materials, only mixed gasses shall be used. Disadvantages are a globular metal transfer and weld spatter (metal losses about 15%). Other suitable gasses are Ar with additions of CO2 like i.e. 80% argon 20% CO2 and 85 Ar 15 CO2). These gasses maintain a stable arc and give little spatter. The latter mixture is recommended when deeper penetration is required (e.g. thicker plate). The purity of the shielding gasses used and its flow shall be stated on the WPS.

For references see: DEP 30.10.60.18 dd. June 2003 page 6 clause 6.1 and 6.6.


9.4.2.2 Flux cored wire (ISO process number 136) When welding with flux cored wires, the chemical composition of the deposited weld metal shall match the composition of the base material. The filler wires used should be compatible with the type of gas. In case of active gasses like CO2, de-oxidizing elements shall be present in the filler wire. For welding these materials, only mixed gasses shall be used. Disadvantages are a globular metal transfer and weld spatter (metal losses about 15%). Other suitable gasses are Ar with additions of CO2 like i.e. 80% argon 20% CO2 and 85 Ar 15 CO2). These gasses maintain a stable arc and give little spatter. The latter mixture is recommended when deeper penetration is required (e.g. thicker plate). The purity of the shielding gasses used and its flow shall be stated on the WPS.

For references see: DEP 30.10.60.18 dd. June 2003 page 6 clause 6.1 and 6.6.

Self shielding flux cored wires shall not be used.


9.4.3 GTAW (ISO process number 141) For root-passing the TIG-process may be used, using the type of wire matching the chemical composition and the tensile strength of the base material. There shall be no oxidizing element as oxygen in the shielding gas used; such to avoid oxidation of the tungsten electrode. When welding the root and the first pass, the reverse side of the weld may be protected to prevent oxidation.


9.4.4 SAW (ISO process number 121) When using the SAW process the chemical composition and the mechanical properties of the deposited weld metal shall match those of the base material. Using welding fluxes with alloying additions is prohibited.





9.5 WELDING PREPARATION Flame cutting, plasma-arc cutting as well as mechanical processes may be used for weld preparation. When thermal cutting or arc-air gouging is performed, adequate pre-heating shall be applied to prevent hardening. See 6: Welding Techniques of the different types of steel. To prevent excessive carbon pick-up during arc-air gouging, a power source with a minimum open voltage over 80 V shall be used. Besides, the pressure and the amount of compressed air shall be in accordance with the recommendations of the supplier manufacturer. When gouging has been carried out, the edges shall be dressed back for a minimum of 2 mm by grinding or machining, to eliminate the zone with carbon pick up

For references see: DEP 30.10.60.18 dd. June 2003 clause 8.


9.6.1 General In this chapter the different types of these steels will be dealt with separately.

9.6.1.1 PWHT PWHT temperature ranges and holding time for various materials shall be in accordance with the design code. The following rules also apply:

For optimum high temperature creep properties, the lower side of the temperature range is normally used.

For maximum softening the higher side of the temperature ranges is used. The welding procedure qualification tests shall determine whether the temperature range and holding times are adequate to meet the requirements.

Notes: 1. The carbon content of Cr-Mo steels influences the choice of the PWHT temperature. The

higher specified temperature shall be used to obtain the required hardness for materials with a higher carbon content.

2. For quenched/normalized and tempered steels, the PWHT temperature shall be such to avoid an unacceptable decrease of mechanical properties of the parent metal, PWHT temperature shall be at least 20C below the tempering temperature.

3. In case of dissimilar metals the PWHT temperature shall be approved by the principal.

Also see BWP: Welding dissimilar metals.

No welding or heating shall be carried out after the final PWHT. NDE for acceptance purposes shall be carried out after the final PWHT.

9.6.1.2 0,3 and 0,5% molybdenum steels

Consumables 0,3 Mo-steels shall be welded with basic low hydrogen consumables depositing 0,5 Mo. 0,5 Mo-steels shall be welded with matching (for SMAW basic low hydrogen) consumables (see 4.1 of this BWP).

Pre-heating The weldability of 0,3 0,5 Mo-steels depends on the carbon content and the carbon equivalent. The pre-heat temperature will mostly be within the range of 100 150C.

Heat input The heat input shall be specified in the WPS, so the maximum hardness in the base material, heat affected zone and weld metal shall not exceed:

248 HV10 for steels in process service. Inhoudelijk beheer: CEI/6 Pagina: 33 van 91 Filenaam: 04002030.doc Rev.: A



290 HV10 for ferritic materials in utility service (steam, air, water). For references see: DEP 30.10.60.18 dd. June 2003, clause 12.6.1.3.

Interpass temperature According API 582 the max. interpass temperature is 315C.

Cooling down Cooling down to ambient temperature shall be done under an insulating cover. Welds shall not be allowed to cool down until at least half of the wall thickness has been welded.

PWHT After welding a PWHT shall be carried out, in accordance with the design code. For 0,3 0,5% Mo steels in hydrogen service, PWHT is required irrespective of the wall thickness.

Also see the remarks made in 6: General.

9.6.1.3 1 Cr 0,5 Mo and 1,25 Cr 0,5 Mo steels

General Weldability is related to the carbon, chromium and molybdenum content, i.e. the higher the content of these elements, the more precautions shall be taken to avoid hydrogen cracking. Pre-heating, interpass temperature, post heating and PWHT shall be strictly controlled.

Consumable These materials shall be welded with low hydrogen consumables, depositing a matching chemical composition.

Pre-heating Pre-heating shall be applied between 150 200C.


248 HV10 for steels in process service 290 HV10 for ferritic materials in utility service (steam, air, water) For references see: DEP 30.10.60.18 dd. June 2003, clause 12.6.1.3.

Interpass temperature According API 582 the max. interpass temperature is 315C

Bead shape Welding shall be done using the stringer bead method only.

Post weld heat treatment For thicknesses between 10 and 30 mm intermediate post weld heating shall be applied after welding, prior to cooling to ambient temperatures, in accordance with tabel 1 as shown below, unless a full PWHT is carried out intermediately.

Table 9-1: Post-heating holding time in hours

Plate thickness (mm) 150C 200C 250C 300C

10 20 6 3 2 1,5 21 30 10 7 5 3

For sections thicker than 30 mm an intermediate PWHT at 600 620C shall be carried out for high restraint conditions, e.g. complex nozzle configurations, following immediately after welding without cooling down to ambient temperature.




Final PWHT shall always be carried out. The PWHT temperature for tempered grades shall be at least 20C below the tempering temperature. PWHT temperatures shall be in conformance with the design code unless otherwise specified.


Cooling down For thicknesses up to 10 mm, the cooling down from pre-heat to ambient temperature shall be done under an insulating cover. Welds shall not be allowed to cool down until at least half of the wall thickness has been welded.

9.6.1.4 2,25 Cr 1 Mo and 3 Cr 1 Mo steels These materials are highly susceptible to cracking, therefore extreme care shall be taken when welding is performed.

Consumables These materials shall only be welded with low hydrogen basic consumables, depositing a matching chemical composition. The weld metal shall be checked prior to use for the specified amounts of Cr and Mo. Alloying additions to the weld metal are allowed only via the filler wire. Alloying additions via welding flux or coating are not allowed, except for compensating alloy burn-off during welding.

Pre-heating Pre-heating shall be applied between 200 300C. Pre-heating shall be carried out regardless of wall thickness.


248 HV10 for steels in process service. 290 HV10 for ferritic materials in utility service (steam, air, water). For references see: DEP 30.10.60.18 dd. June 2003, clause 12.6.1.3

Interpass temperature According API 582 the max. interpass temperature is 315C The interpas temperature shall not drop below the pre-heat temperature during welding.

Bead shape Welding shall be applied only in the stringer bead method.

Post weld heat treatment For thicknesses between 10 and 30 mm intermediate post weld heating shall be applied after welding, prior to cooling to ambient temperatures, in accordance with table 1, unless a full PWHT is carried out intermediately after welding. For sections thicker than 30 mm an intermediate PWHT at 600 620C shall be carried out, immediately after welding without cooling down to ambient temperatures. Final PWHT shall always be carried out. The PWHT temperature for tempered grades shall be at least 20C below the tempering temperature. PWHT temperatures shall be in conformance with the design code unless otherwise specified.





Cooling down For thicknesses below 10 mm, the cooling down from pre-heat to ambient temperature shall be done under an insulating cover. Welds shall not be allowed to cool down until at least half of the wall thickness has been welded.

9.6.1.5 9 Cr 0,5 Mo, 9 Cr 1 Mo and 9 Cr 1 Mo modified These materials are susceptible to cracking by hydrogen and hard microstructure.

Consumables These materials shall only be welded with low hydrogen basic consumables, depositing a matching chemical composition. 9 Cr 1 Mo modified differs from standard 9 Cr 1 Mo steel insofar that alloy additions (vanadium, nitrogen, nickel, niobium) enhance the properties. Weldability is comparable with 9 Cr 1 Mo steels. Due to the difference in chemical composition the order/requisition form should clearly specify consumable type required (e.g. state explicitly whether 9 Cr 1 Mo modified consumables are required).

Pre-heating Due to the higher Cr-content these materials are more susceptible to air-hardening. To prevent cracking caused by hydrogen an hard microstructure, pre-heating shall be applied between 200 300C, regardless of wall thickness.

Heat input The heat input shall be specified in the WPS, so the maximum hardness in the base material, heat affected zone and weld metal shall not exceed 290 HV10 for ferritic materials in utility service (steam, air, water)

For references see: DEP 30.10.60.18 dd. June 2003, clause 12.6.1.3.

Interpass temperature According API 582 the max. interpass temperature is 315C The interpass temperature shall not drop below the pre-heat temperature during welding.

Bead shape Welding shall be done using the stringer bead method only.

Post weld heat treatment For thicknesses between 10 and 30 mm intermediate post weld heating shall be applied after welding, prior to cooling to ambient temperatures, in accordance with table 1, unless a full PWHT is carried out intermediately. For sections thicker than 30 mm an intermediate PWHT at 600 620C shall be carried out, immediately after welding without cooling down to ambient temperature. Final PWHT shall always be carried out. The PWHT temperature for tempered grades shall be at least 20C below the tempering temperatures. PWHT temperatures shall be in conformance with the design code unless otherwise specified.


Cooling down For thicknesses below 10 mm, cooling down from pre-heat to ambient temperature shall be done under an insulating cover Welds shall not be allowed to cool down until at least half of the wall thickness has been welded.




9.7 WELDING PLATES For weld fit-up, the use of backing, pre-heat requirements, welding conditions, weld application, PWHT: see DEP 30.10.60.18 dd. June 2003 clause 8 and 9.1. The weld shall be completed before the pre-heat temperature is lowered, if at least 50% of the weld has been completed. See: DEP clause 8.1.

9.8 WELDING PIPES For welding pipes all the processes as mentioned in clause 4 may be used. For weld fit-up, the use of backing, welding conditions, weld application and so on: see DEP 30.10.6018 dd. June 2003 clause 8.1. The weld shall be completed before the pre-heat temperature is lowered, if at least 50% of the weld has been completed. See: DEP 30.10.60.18 dd. June 2003 clause 8.1

9.9 POST WELD HEAT TREATMENT After welding, a heat treatment shall be carried out as specified on the WPS. For references see: API 582 clause 9.

DEP 30.10.60.18 dd. June 2003 clause 9.1.

For minimizing the hydrogen content after welding, a soaking treatment may be performed for 2 hrs at 200C. Cooling down to ambient temperature directly after welding is then prohibited. For post heat holding times: see DEP 30.10.60.18 dd. June 2003 clause 13.2. Depending of the amount of weld metal, the welding-sequence, the wall thickness and the application of stress relieving, may be considered.

Also see the remarks made at 6: General in this document.

9.10 REPAIR WELDING For repair welding the processes, mentioned in clause 4 of this document, may be used, except the SAW-process for the applications as mentioned in DEP 30.10.60.18 dd. June 2003, clause 5.2.6.3. For repair welding all the requirements for welding, as stated in this document, shall apply.

Also see BWP: Repair welding and Welding dissimilar metals.





10. PRE-HEAT AND POST WELD HEAT TREATMENT

10.1 GENERAL REQUIREMENTS Heat treatments may be carries out either full-body or locally, depending on:

Type of heat treatment Material of composite of substrate Number and sizes of substrate Configuration of work piece Availability and cost of energy Required accuracy of heat treatment Welding process and welding consumable Code requirement. Heat treatment be carried out in accordance with a qualified heat treatment procedure specification. The heat treatment procedure shall be reviewed and approved by the Principal before the Heat Treatment activity takes place. After the heat treatment the registration form shall be submitted to Shell Pernis and Shell Moerdijk inspection department. For furnace heat treatment the temperature at the time of insertion of the work piece shall not exceed 400C. For special applications like work piece with wall thickness over 60 mm, or work piece of very complicated shape or double wall, a maximum insertion temperature of 300C is required. During heating up and cooling down, no temperature gradient shall exceed:

100C/m in axial direction, nor 40 C/m in tangential direction to be checked by temperature recorder.

For wall thicknesses of pipe or plate upto and including 25 mm the rate of heating shall not exceed 200-250C/h. For thicknesses of pipe or plate over 25 mm the rate of heating shall not exceed:

5500/tC/h (t = maximum section thickness) or

55C/h, whichever is greater.

During the heat treatment the furnace atmosphere shall be selected so as to avoid excessive oxidation/surface attack. There shall be no direct flame impingement. During cooling the workpiece must remain in the furnace until the temperature of all parts with wall thickness over 25 mm has fallen below 400C. Hereafter cooling in still air is allowed. During furnace cooling no temperature gradient shall exceed:

100C/m in axial direction, nor 40C/m in tangential direction,

to be checked by temperature recorder.

The workpiece shall be cooled to 400C whereby the cooling rate is limited as follows:

For wall thicknesses of pipe or plate < 25mm 275C/h

For wall thickneses >= 25 mm 6875/t (t = maximum section thickness




or

55C/h whichever is the greater.

The pre-heat and postweld heat treatment temperatures for various materials are given in the table below.

10.2 PRE-HEAT REQUIREMENTS Amendments to DEP 30.10.60.18-Gen May 2004. Pre-heating of the parent metal prior to any welding, tack welding and thermal cutting may be necessary to avoid cold cracking of certain ferritic steels in the weld and HAZ. Pre-heating could also be required for welding of non-ferrous materials to remove moisture or to prevent hot cracking Temperature control can be carried out with temperature sensitive crayons, digital pyrometers, contact thermometers or calibrated thermocouples. Thermocouples must be calibrated in accordance with IEC 584-2 (highest class). Temperature recorders must be calibrated twice a year. Calibration to be recorded on a registration list.

Material Pre-heat Post-weld heat treatment Wall thickness

mm Min. temp.C

1) Wall thickness

mm Temp.rangeC

min.-max. Holding time; min. per mm

wall thickness 2)

Carbon Steel 25 > 25

20 20 3)

32 > 32

Optional 4) 580- 620

620 - 64011)

2.5

Fine grained and low nickel alloy steels

25 > 25

Optional 4) 100-150

32 > 32


2.5

0.3Mo 0.5Mo steel 20 > 20

20 100-150

20 > 20


2.5

1Cr 0.5Mo 1.25Cr 0.5Mo

all 100-150 all 640- 680 5) 680- 720 6) 7)

2.5 8)

2.25Cr 1Mo all 200-250 all 630- 680 5)7) 680- 720 6) 7) 720- 750 7)9)

5 8)

5Cr 0.5Mo 9Cr 1Mo

all 200-250 all 680- 720 5) 7 720- 760 7) 9)

5 8)

12-17 Cr martensitisch rvs

all 200-300 all 700- 790 10) 2,5

Tabellen ex DEP 30.10.60.18-Gen rev.1986 and a revision d.d. 12-09-2006

1) If ambient temperature is below 5C pre-heating at 40C is recommendable. 2) Minimum holding time 1 hour. 3) Low hydrogen filler metals have to be used. 4) PWHT is required for Ceq 0,45 of C 0,23. 5) For optimum high temperature creep properties in general the lower side of the temperature range is used. 6) Temperature range in the case of service for hygrogen (H2) or general refinery services. 7) Minimaal 10 below refinement temperature. 8) See table 1. 9) Temperature range for maximum softening. 10) PWHT temperature is dependent of the PWHT temperature of the base metal.




Opwarm- en afkoelsnelheid

Activiteit Wanddikte Vrij gebied inC Begrensde gebied inC

Opwarmen t 25 mm 0 300 T > 300, snelheid maximaal 200C/uur Opwarmen t > 25 mm 0 300 T > 300, snelheid maximaal 5500/t inC/uur, of 55C/uur (welke de

grootste is) Afkoelen t 25 mm 400 0,

onder isolatie T > 400, snelheid maximaal 200C/uur

Afkoelen t > 25 mm 400 0, onder isolatie

T > 400, snelheid maximaal 6875/t inC/uur, of 55C/uur (welke de grootste is)




11. WELDING OF LOW ALLOY NICKEL STEELS (1%, 2.5%, 3.5%, 5% and 9% Ni).

Shell International Oil Products Best Welding Practice and Procedures

11.1 INTRODUCTION Some percents of nickel are added to C-Mn-steels to make it possible to use these steels to temperatures down to 196C. In principle there are five types:

1% nickel, application down to 50C. 2.5% nickel, application down to 80C. 3.5% nickel, application down to 120C. 5% nickel, application from 120 till 170C. 9% nickel; application down to 196C. The lat

Documents

Best Welding Practices.pdf