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Splicing of Steel Pipe Piles by WeldingUpdate 05/2008

Steel pipe piles are used, for instance, in foundations of buildings, bridges and port facilities.These instructions apply to the splicing by welding of steel pipe piles installed in the ground. On site steel pipe piles can be joined by welding. The welds are required to withstand all loads during installation and service. Recommendations are given for actual welding work, requirements on weld quality and inspection of welds.

CFI 03.006EN/05.2008 1

Splicing of Steel Pipe Piles by Welding

• Steel grades for pipe piles Table 1

Steel grade Chemical composition, max. Mechanical properties Impact strength CEV C Mn P S fy min fu A5 min T KV min max [%] [%] [%] [%] [%] [MPa] [MPa] [%] [°C] [J]

S355J2H 0.39 0.22 1.60 0.035 0.035 355 490-630 20 -20 27

S440J2H 0.39 0.18 1.60 0.020 0.018 440 490-630 17 -40 * 27

S550J2H 0.39 0.12 1.80 0.025 0.015 550 600-760 14 -20 * 27

X60 0.43 0.15 1.60 0.030 0.030 413 517 18 0 27

X70 0.43 0.15 1.70 0.030 0.030 482 565 18 0 27

*) With material thicknesses exceeding 10 mm, impact strength requirement must be agreed separately.

• Steel Grades for Steel PilesPipe piles are made of the structural steels presented in Table 1 and other high strength steels. All presented steels are highly weldable.

• Welding PlanA detailed welding plan, acceptable by all involved parties, is drawn up as part of the piling plan. The welding plan is to include the following:

• steel grade• weld quality level• welding procedure• welding consumables• possible preheating• welding conditions• types of joint preparation• welding positions• a welding procedure specifi cation (WPS)• welding procedure tests, when required• production weld test, when required• welder qualifi cations• after-treatment of welds, if required• weld inspection instructions

• Welding Quality RequirementsThe welding, inspection, testing, and related functions are to meet at least the requirements of Standard EN ISO 3834-4 (Quality requirements for fusion welding of metallic materials. Part 4: Elementary quality require-ments). More comprehensive specifi cations can be applied by mutual agreement of the parties.

Welded joints are usually suffi ciently strong and ductile provided that the welding procedure has been carried out carefully. In exacting applications, the mechanical properties of welded joints may also be ensured through welding procedure tests and/or production weld tests.

Imperfections such as gas pores, slag inclusions and lack of fusion reduce the strength of a weld. For this reason, quality requirements have been set for welds, defi ned as weld quality levels in accordance with Stand-ard EN-ISO 5817 (Welding. Fusion-welded joints in steel, nickel, titanium and their alloys [beam welding excluded]. Quality levels for imperfections). The quality level should be chosen considering the static and dynamic loads on the structure, the service conditions of the structure, and the consequences of possible damage as well as the treatments to be carried out after welding. As to the loading of the structure, loads during installation as well as service must be considered.

Unless otherwise specifi ed in the drawings or contract documents, Quality Level C (Intermediate) can be considered the general requirement for splice welds in steel pipe piles. Level C corresponds to good workshop engineering practice that qualifi ed welders attain under ordinary workshop and site conditions. Quality Level D (Moderate) can be chosen for less demanding welds, for example, when the pipe pile is not a load-bearing structure but only a casing. An unnecessarily high Quality Level results in extra costs.

The most common weld defects, their causes and remedies are presented on pages 7 and 8.

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Splicing of Steel Pipe Piles by Welding

• Qualifi cation of WeldersThe welders must have passed the test indicated in Standard EN 287-1 (Qualifi cation test of welders. Fusion Welding. Part 1: Steels). The welding contractor must en-sure that the welders carry valid certifi cates of qualifi cation.

Qualifi cation tests must correspond to the requirements of the work. Factors to be considered include welding procedure, type of joint, steel grade, material thickness, external pipe diameter, and welding position as indicated in the standard. Qualifi cation test welds are normally to be made on pipe. Test welds on plate are acceptable with pile diameters over 500 mm.

In the case of manual metal arc welding with covered electrode, the welder’s competence can be ascertained, for example, by a single-sided test weld on pipe without backing as follows:

• Production Weld Tests and Welding Procedure TestsBefore starting the work, the contractor is to carry out a production weld test under conditions corresponding to those on site where two pipe pile sections are welded to-gether in accordance with the WPS. The welded length shall correspond to about a quarter of the overall joint length. At least one piece measuring about 100 x 100 mm

containing a weld is cut out of what appears to the eye to be the most critical area of the weld. One of the cross-sectional surfaces of the weld is ground and inspected visually. The result must meet the requirements for the specifi ed weld quality level concerning imperfections vis-ible to the eye. Special attention is to be paid to complete penetration. The results of the production weld test are to be recorded in the appropriate documents.

In the case of steel pipe piles, the welding procedure test in accordance with Standard EN ISO 15614-1 (Specifi -cation and qualifi cation of welding procedures for metal-lic materials. Welding procedure test. Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys) can usually be omitted unless separately speci-fi ed by the designer, client or authorities in the contract documents. They may also specify a smaller scope for the welding procedure test than required by the standard that includes, for example, only a transverse tensile test, a bending test and a macro section. A welding procedure test is also appropriate if the contractor has no previous experience from welding the steel grade in question or the welding procedure or the fi ller material to be used.

The welding procedure test is carried out as specifi ed in Standard EN ISO 15614-1. The test involves welding a test plate representing production welds and performing the appropriate tests on it. The welding procedure test is specifi c to each manufacturer, base material, welding procedure, position, type of joint and material thickness, as defi ned in the standard.

• Welding ProceduresManual metal arc welding is the conventional welding procedure for splicing steel piles on sites. It is a versatile and fl exible method that uses simple, easily transport-able equipment.

Flux cored arc welding is a more modern welding proce-dure. Its advantages include high effi ciency, consistent weld quality and suitability for mechanised production. Different types of welding nozzle conveyors attachable to the pipe are available for mechanised fl ux cored arc welding. These devices facilitate work in cramped spac-es, such as underpinning sites, where piles must be positioned close to a wall. The space between pile and wall may be as narrow as 150 mm. When welding with a shielding gas, it may be necessary to use screens to prevent the detrimental effect of wind and draught. There are also cored fi ller wires on the market that can be used without shielding gas.

Workshop welding may be carried out by any welding procedure for non-alloy steels.

• Example of qualifi cation test for Table 2 manual metal arc welder EN 287-1: 111 T BW W01 B t10.0 D168 PC ss nb

Explanation:

111 Metal arc weldingT PipeBW Butt weldW01 Group of parent materials (qualifi es for steel S355 but not the higher strength steel gradesB Basic electrode coatingt10.0 Tested on pipe of 10 mm wall thickness, qualifi es for thicknesses t = 3–20 mmD168 Tested on pipe 168 mm in diameter, qualifi es for diameters D >_ 84 mmPC Welding position PC, pipe in upright position, also qualifi es for horizontal position (PA) (Welding position codes in accordance with EN ISO 6947 are shown on page 8)ss Single side weldingnb No backing (also qualifi es for welding with backing)

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Splicing of Steel Pipe Piles by Welding

• Selection of fi ller material Table 3.

Steel grade Mechanical properties of weld metal (EN ISO 2560 and EN 757 covered electrodes and EN 758 and 12535 tubular cored electrodes)

Yield strength1 Impact Covered electrode, Tubular cored electrode, strength2 examples examples

S355J2H 35 2 ESAB OK 48.00 TRI-MARK TM-770, ESAB OK Tubrod 15.14

S440J2H 46 2 ESAB OK 55.00, ESAB OK 48.08 TRI-MARK TM-770, ESAB OK Tubrod 15.14

S550J2H 55 2 ESAB OK 74.78 TRI-MARK TM-881 K2, ESAB OK Tubrod 15.07

X60 42 2 ESAB OK 48.00 TRI-MARK TM-770, ESAB OK Tubrod 15.14

X70 50 2 ESAB OK 74.78 TRI-MARK TM-881 K2, ESAB OK Tubrod 15.11

1) Yield strength values of all-weld metal35 = minimum yield strength: 350 MPa42 = minimum yield strength: 420 MPa46 = minimum yield strength: 460 MPa50 = minimum yield strength: 500 MPa55 = minimum yield strength: 550 MPa2) testing temperature of 47 J impact energy of all-weld metal: 0=0°C, 2=-20°C.

• Welding Consumables (Filler materials)The standards for covered electrodes are EN ISO 2560 (Welding consumables. Covered electrodes for manual metal arc welding of non-alloy and fi ne grain steels. Clas-sifi cation) and EN 757 (Welding consumables. Covered electrodes for manual metal arc welding of high strength steels. Classifi cation).

The standards for cored wires and rods are EN 758 (Welding consumables. Tubular cored electrodes for metal arc welding with and without a gas shield of non-alloy and fi ne grain steels. Classifi cation) and EN ISO 18276 (Welding consumables. Tubular cored electrodes for gas-shielded and non-gas-shielded metal arc welding of high-strength steels. Classifi cation).

Filler materials are to meet the above standard specifi ca-tions. They are chosen on the basis of the strength and impact-strength requirements of the steel grade of the piles according to Table 3.

When welding together pile sections of different strength or type, the fi ller is generally selected according to the softer or less alloyed steel grade. However, when for in-stance welding fi xtures, etc. to a pile, the fi ller is selected on the basis of the more alloyed steel (pile) in order that the fi ller to be incorporated into the pipe wall is suffi cient-ly alloyed.

Covered electrodes must be of the basic type, indicated by the letter B in the designation.

When necessary, subject to agreement between the parties, the root run can be welded with fi ller material of lower strength than the parent metal.

The coatings of covered electrodes and some cores of tubular cored electrodes being hygroscopic, they easily absorb moisture from ambient air. Moisture may cause gas pores, splatter and, in the worst case, hydrogen cracking in the weld. Therefore, it is important to handle and store these products carefully.

The contractor is obliged to ensure that fi ller materials remain dry on site. They are to be stored in a dry and warm space which prevents moisture from condensing inside the package due to variations in temperature.

44

Splicing of Steel Pipe Piles by Welding

welding. For mechanised welding bevels are to be made by turning.

As pipe piles are welded from the outside, the type of joint preparation must be such as to enable suffi cient penetration and an even root reinforcement on the inside. It is particularly important to have a proper air gap to ensure full penetration.

Recommendations for correct types of joint preparation are given in Standard EN ISO 9692-1 (Welding and allied processes. Recommendations for joint preparation. Part 1: Manual metal-arc welding, gas-shielded metal arc welding, gas welding, TIG welding and beam welding of steels). Single bevel preparation and single V prepara-tion are the most common types of joint preparation. Single V preparation is suitable for welding in all posi-tions. Single bevel preparation is preferable for welding upright piles.

Single V joint preparation is used to splice full-length piles delivered from the works. If piles need to be cross-cut on site, the groove may also be prepared as a single bevel preparation, that is, a square edge against a bevel-led edge. Pile ends damaged during transport or installa-tion must be repaired before splicing. Recommendations for correct types of joint preparation for welding without backing are presented in Fig. 1.

Fig. 1 Types of joint preparation for welding without backing.

At the actual welding site, fi ller materials are to be pro-tected from rain, etc. and electrodes to be kept in a sepa-rate heated quiver from which the welder withdraws them one at a time. Electrodes are also available in hermeti-cally sealed packages. Each package contains just a few electrodes which can be used within 4 hours of opening the package without the risk of humidifi cation.

Moist or otherwise damaged fi ller materials must not be used. Wet electrodes can be dried according to the man-ufacturer’s instructions, for example at +300°C to +400°Cfor 2 to 3 hours.

When welding is fi nished, the coils of tubular cored elec-trode should be removed from the machine and taken to a dry and warm place for storage.

• Welding ConditionsWeather is a major factor affecting weld quality and the welders’ working conditions. Welding conditions that en-able attaining the planned quality level must be provided. If necessary, the welding site should be appropriately protected against wind and rain, and it should also be suffi ciently lit. Anvils should be level and stable so the welder can carry out his work properly and safely.

For welding in sub-zero conditions, it is important to provide tolerable working conditions for the welder. When ambient air is cold, moisture condenses on metal surfaces which requires preheating them to +50 to +100°C to remove the moisture, even though the steel itself requires no preheating.

Proper earthing is essential in assuring weld quality. The earth cable must be dimensioned to match the weld cable and be connected directly to the workpiece. The earthing point must be metallically clean.

Under humid and wet conditions, the welder must be properly protected against electrical accidents.

• Joint PreparationPile pipes are usually delivered from the works with the ends bevelled for welding (30°) and a root face of 1.6 mm ± 0.8 mm. On site, piles are usually cut by a fl ame cutting or grinding. It is recommended that the cutting line be marked all the way around the pile circumference in order that the cut is made perpendicular to the pile’s centre line. Manual cutting often leaves a ragged pile end and which is not suffi ciently straight. Such defects must be repaired with a grinder. The bevels are to be pro-duced by fl ame cutting and/or grinding. Flame-cut sur-faces must always be ground to render them clean for

In splice welding of piles, the use of backing on the inside of the groove is recommended. A fi xed backing should be of the same steel as the pile sections to be connected. Ceramic backings can also be used. The backing should be of suffi cient width, usually no less than 50 mm, and at least 5 mm thick. The backing is to be fi tted symmetrically in relation to the groove and fastened in advance by inter-mittent welds (fi xed backing) or, for instance, with adhe-sive tape (ceramic backing) inside the pile. When backing is used, the weld reinforcement inside the pipe is to be ground level with the pipe surface. No air gap is allowed between the backing and the pipe wall. Recommended types of joint preparation for welding with backing are shown on the next page in Fig. 2.

0-2

0-2

0-2

2-42-4

2-4

60°

60°30°

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Splicing of Steel Pipe Piles by Welding

• PreheatingPreheating decelerates the cooling of the welded joint and lessens the degree of hardening. This prevents the forma-tion of a hard and brittle zone in the HAZ, and thereby the development of hydrogen cracks. The need of preheating depends on steel grade, material thickness, fi ller metal (hydrogen content), heat input and welding conditions. High-strength steel, thick material, high hydrogen content (e.g. moist electrodes) and low heat input are factors that increase the need of preheating.

More detailed instructions for the selection of preheating can be found in professional literatur. Usually, for exam-ple, no preheating is required when welding S355 steel less than 20 mm thick provided that dry basic electrodes are used. Moist electrodes must always be dried before use. When welding at temperatures below +10°C, the pile ends are to be preheated to +50 to +100°C before starting the work.

Fig. 3 Joint preparation for fully mechanised welding.

The types of joint preparation presented in Fig. 1 can be used for mechanised welding, provided that the root run is deposited manually. The types of joint preparation shown in Fig. 2 can be used in fully mechanised welding. There, also the root run is preferably deposited by machine. A special type of joint preparation has been developed for that where a machined “tongue” functions as backing (See Fig. 3). With this type of joint prepara-tion, the welding parameters should be selected so that the machined backing (“tongue”) melts, full penetration is achieved, and lack of fusion and root defects (“incom-plete penetration”) are avoided

Fig. 2 Types of joint preparation for welding with backing.

• WeldingPile ends must be clean inside and out for a distance of about 50 mm on each side of the groove. If necessary, any impurities, grease, moisture, rust, etc. is to be re-moved as they are likely to cause welding defects and thereby impair the quality of the weld. Any possible back-ing must also be cleaned, if necessary.

After joint preparation and cleaning, the pile ends are centred and carefully fi tted together so that the inner sur-faces of the two pile sections are aligned and the re-quired air gap remains between them (see Figs. 1 and 2). The fi tting of the pile ends together can be facilitated by welding guide blocks onto one pile; they are removed after tacking. There also are special devices on the mar-ket for centring pipes. Wedges, electrode core wires (e.g. 3.2 mm), etc. can be used to ensure the required gap width; they are removed after tacking. If the gap width varies, it must be ensured that it meets the minimum re-quirement even at its narrowest point. Any difference in root face height must be eliminated by grinding before aligning the pile sections. Thereafter, the pile ends are connected by short tack welds. If a tack weld is left in the groove as part of the root run, the ends of tack welds must be carefully ground to remove any crater pipes and to ensure full penetration.

A 2.5 mm electrode is recommended for the manual welding of root runs. Filling and capping runs are usually made with 3.2 mm electrodes. With thick-walled pipes, even thicker electrodes may be used for fi lling and cap-ping runs. The most common wire diameter of a tubular cored electrode is 1.2 mm. However, tubular cored elec-trodes ranging from 0.9 mm to 1.6 mm are available de-pending on the intended application and requirements. The supplier of the welding apparatus provides the nec-essary training for mechanised welding.

• Inspection of WeldsInspection of welds is conducted in accordance with the instructions of the contract documents concerning the procedures and scope of inspection. A visual inspection is always carried out. Ultrasonic testing is a suitable form of non-destructive testing (NDT).

All welds are fi rst examined visually. Visual inspection is aimed to detect any imperfections in weld dimensions, misalignments, undercuts, defects breaking the surface, etc. An NDT inspection of welds is conducted only after a weld has passed visual examination.

The scope of ultrasonic testing is agreed between the parties. It is typically 10 per cent. An inspection covers the entire length of a weld, that is, one out of ten welds

°60

1

10-2

0-24-6

4-6

4-6

0-2

60°

60°30°

66

Splicing of Steel Pipe Piles by Welding

Cracks

• moist electrodes: - store electrodes in a dry place; on site, keep them in a heated quiver• thick material: - apply higher arc energy - preheat pile ends

is inspected completely, unless otherwise agreed. Inspection always starts with the fi rst weld where the occurrence of any internal defects in the weld (incom-plete fusion, gas pores, slag inclusions) and root-side imperfections (incomplete penetration, excess weld metal) is examined. Defects that exceed the limit values for the weld quality level are repaired. Repaired welds are reinspected and two additional welds as well (the so-called penalty rule). An NDT inspection may only be conducted and assessed by an inspector qualifi ed accord-ing to EN 473 (Non destructive testing. Qualifi cation and certifi cation of NDT personnel. General principles).

Inspection records are always kept of each inspection.

• Welding defectsThe following is a presentation of the most common welding defects in manual metal arc welding, their causes and remedies.

Slag inclusions

• incomplete slag removal: - remove any slag carefully after each run• runs welded in incorrect order: - ensure that runs are deposited without leaving narrow

cavities• bad shape of reinforcement: - grind the layer more even• too low welding current: - use higher welding current

Gas pores

• moist electrodes: - store electrodes in a dry place; on site, keep them in a heated quiver - dry moist electrodes• impurities on groove surfaces: - clean surfaces before welding• excessive arc length: - weld with a suffi ciently short arc• too low welding current: - use higher welding current

Incomplete penetration (root defect)

• too narrow gap in groove: - use suffi ciently wide gap• too wide root face in groove: - use suffi ciently narrow root face• too thick electrode in root run: - use thinner electrode• too low welding current in root run: - increase welding current

Undercut

• too high welding current: - reduce welding current• improper movement of electrode: - move electrode correctly• too fast weaving of electrode: - weave electrode more slowly

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Splicing of Steel Pipe Piles by Welding

• Designations of the most common welding positions (EN ISO 6947)

The accuracy of the contents of these instructions has been inspected with utmost care. However, we do not assume responsibility for any mistakes or direct or indirect damages due to incorrect application of the information. Right to changes is reserved.

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Too large reinforcement

• too wide gap in groove: - use smaller gap• too high welding current: - use lower welding current in welding root run• too slow electrode movement: - move electrode faster when welding root run

Lack of fusion

• too narrow groove: - widen groove (groove angle or gap)• too slow or too fast electrode movement: - adjust the speed as appropriate• too low or too high welding current: - use appropriate welding current for the case• incorrect pointing of electrode in the groove: - point electrode so that it fuses the material under

neath

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