Material requirements

Maurice Stewart , in Surface Production Operations, 2016

3.2.1.3.5 Spiral-welded pipe

Spiral-welded pipe is produced from coils of steel that are unwound and flattened. The flattened strip is formed by angled rollers into a cylinder of the desired diameter. Interior and exterior SAW seal the spiral seam. At the end of the coil, a new coil is butt-welded to the trailing edge of the pipe, forming a cross seam. The pipe is cut to length and the ends are beveled if required. Spiral-welded pipe is primarily used for water distribution service. Spiral-welded pipe is available in sizes from 24   in. (60   cm) to 144   in. (365   cm).

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The behaviour of welds in service

J.F. Lancaster , in Metallurgy of Welding (Sixth Edition), 1999

Hydrogen pressure-induced cracking

This is a problem that arose in The Gulf in the 1970s. A spiral-welded pipe carrying sour gas ruptured only a few weeks after commissioning. The failures, which occurred preferentially adjacent to the welds, were due to H2S corrosion, which saturated the metal with hydrogen and produced the step-like cracking described in the previous section, but not necessarily restricted to the weld region. Several other lines were affected.

The steel was strip containing a substantial amount of Type II manganese sulphide inclusions and was therefore particularly susceptible to delamination. Subsequently steelmakers have offered sulphur contents down to 0.002% (20   ppm) together with rare earth treatment.

However, a second problem arose. In continuous casting, manganese and phosphorus segregate to the central region, which results in a hard band in the rolled product. This may be subject to hydrogen cracking even in the absence of laminar inclusions. To avoid such segregation, manganese and phosphorus contents are reduced and the liquid steel is subject to electromagnetic stirring during the continuous casting operation.

Line pipe that may be employed in sour service is usually subject to testing in a simulated environment: either seawater saturated with H2S or a similar solution acidified with acetic acid.

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Manufacturing, testing, and operational techniques to prevent sour service damages

Mohammed A. Al-Anezi , ... Saad M. Al-Muaili , in Handbook of Materials Failure Analysis with Case Studies from the Oil and Gas Industry, 2016

2.1 SOHIC Failures

There is no industry or international standard that prohibits the use of spiral pipe in wet sour applications. Spiral welded pipe fabricated from HIC-resistant coil failed after 7 months of service by SOHIC in wet sour hydrocarbon gas containing 10 mole% of H 2S with the same amount of carbon dioxide (CO2). The calculated pH was 3.4, and the operating pressure and temperature were 390   psig and 52   °F, respectively. The 24-in. outer diameter (OD) with 0.5-in. wall thickness spiral pipe was neither cold expanded nor stress relieved to reduce fabrication and welding residual stresses. Figure 19.1 shows a ring that was cut from the failed pipe. The ring was split axially showing a circumferential gap of more than 1-in., indicative of compressive macroscopic residual stress. The 24-in. long crack ran parallel to the weld seam. The locations of cracks, as seen in Figure 19.2, were 0.2-0.5   in. from the seam weld. Figure 19.3 shows the metallurgical examination that revealed a stacked array of short HIC-like cracks parallel to the rolling direction linked by cracks perpendicular to the overall resultant stress, a characteristic of SOHIC. It should be noted that no SOHIC cracks were observed in the vicinity of the girth welds. Microscopic residual stress measurements were performed using an unflawed spiral welded pipe section and straight seam pipe using ASTM E-837 Blind Hole Drilling technique at Stress Engineering Services in Houston [10]. The residual stress conducted at the internal diameter (ID) surface of the spiral pipe at the centerline of the weld, HAZ, and the far field was 82, 72, and 6   ksi, respectively. The majority of the residual stresses at the OD surface produced a mixture of tensile residual stresses ranging from −   14 to 23   ksi. The actual yield and tensile strengths of the failed pipe were 58 and 74   ksi, respectively, meeting the tensile properties of API 5L grade X52. The maximum Vickers hardness (HV) measured at the base metal, HAZ, and weld was 176 HV using 10   kg load. The residual stresses at the centerline of the weld and 1/16-in. from the weld at the ID surface of the cold-expanded straight seam pipe, which was employed in the same service, but did not fail, were 19 and 16   ksi, respectively. Chemical analysis of the internal corrosion scale inside the pipe using X-ray fluorescence techniques indicated the presence of 10% elemental sulfur. The electron microprobe analysis of inclusions close to the crack location indicated the presence of calcium and aluminum oxides.

Figure 19.1. Ring cut from failed spiral pipe showing compressive macroscopic residual stress.

Figure 19.2. Locations of SOHIC cracks were 0.2-0.5   in. away from the weld.

Figure 19.3. SOHIC at the tip of one crack showing stacking of cracks perpendicular to the applied stress. As polished, Magnification: 50   ×.

A previous SOHIC failure of non-HIC-resistant spiral pipe occurred in 1974 within the company [8]. This 24-in. OD with 0.25 wall thickness pipe failed after 25 days of operation. The wet sour hydrocarbon gas was operating at pressure and temperature of 480   psig and 70   °F, respectively, and contained 2.9 mole% H2S and 8.4 mole% CO2. This historical failure was originally considered as SSC type 1.

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Full Scale Testing of Large Diameter Pipelines

R.J. Pick , ... R.I. Coote , in Pipeline and Energy Plant Piping, 1980

3.3 COMMISSIONING TEST

To commission the loading frame and demonstrate its function a 12.2 metre length of 914 mm diameter, Grade 483 MPa, 11.4 mm wall thickness, spiral-welded pipe was loaded to 90% of its yield strain. The pipe and test facility were extensively strain gauged with 29 strain gauges concentrated in the central region to determine strain levels and pipe behaviour. Measurements of pipe ovality were also made.

For the commissioning test the jack pressure was determined from two Bourdon tube pressure gauges. It was determined that the accuracy of these gauges was ± 3% and therefore for subsequent tests the more accurate servo controlled system described previously was used. Pressure was applied to the jacks in increments of .35 MPa up to 13.8 MPa with strain gauge readings being taken at each increment.

The results from the strain gauges at the pipe centreline on the inside and outside respectively are given in Fig. 3 and compared with the theoretically calculated strains. It can be seen that the strains are behaving linearly, however are approximately 5% less than the theoretically predicted values. This error is considered to be partially due to the lack of accuracy in the pressure measurement (3%) and friction in the loading system and ovalling of the pipe (2%).

Fig. 3. Comparison of measured and theoretical strains during commissioning test (centre strain gauge)

To aid in the design of an internal pressure device and to further explain the discrepancy in measured strains, a study was made of the ovality developed in the pipe during loading. Fig. 4 has been prepared from the results. It should be noted that although the ovality is small it will have an effect on strain levels in the pipe. The effect is complex as ovalling will reduce the moment of inertia of the pipe, increasing the strain levels at a given pressure and will also reduce the distance from the neutral axis to the outer fibre reducing the strain levels.

Fig. 4. Effect of bending on pipe ovality

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Steel Pipe

Roy A. Parisher , Robert A. Rhea , in Pipe Drafting and Design (Fourth Edition), 2022

Manufacturing Methods

Carbon steel pipes can be manufactured using several different techniques, each of which produces a pipe with certain characteristics. These characteristics include strength, wall thickness, corrosion resistance, and temperature and pressure limitations. For example, pipes having the same wall thickness but manufactured by different methods may vary in strength and pressure limits. The manufacturing methods we will mention include seamless, butt-welded, and spiral-welded pipes.

Seamless pipe is formed by piercing a solid, near-molten, steel rod, called a billet, with a mandrel to produce a pipe that has no seams or joints. Figure 2.1 depicts the manufacturing process of seamless pipe.

Figure 2.1. Sizing seamless pipe.

Butt-welded pipe is formed by feeding hot steel plate through shapers that will roll it into a hollow circular shape. Forcibly squeezing the two ends of the plate together will produce a fused joint or seam. Figure 2.2 shows the steel plate as it begins the process of forming a butt-welded pipe.

Figure 2.2. Shaping butt-weld pipe.

The least common of the three methods is spiral-welded pipe. The spiral-welded pipe is formed by twisting strips of metal into a spiral shape, similar to a barber's pole, then welding where the edges join one another to form a seam. This type of pipe is restricted to piping systems using low pressures due to its thin walls. Figure 2.3 shows spiral-welded pipe as it appears before welding.

Figure 2.3. Forming spiral-welded pipe.

Figure 2.4 shows the three pipes previously described in their final form.

Figure 2.4. Manufactured carbon steel pipe.

Each of the three methods for producing pipe has its advantages and disadvantages. Butt-welded pipe, for example, is formed from a rolled plate that has a more uniform wall thickness and can be inspected for defects prior to forming and welding. This manufacturing method is particularly useful when thin walls and long lengths are needed. Because of the welded seam, however, there is always the possibility of defects that escape the numerous quality control checks performed during the manufacturing process.

As a result, The American National Standards Institute (ANSI) developed strict guidelines for the manufacture of pipe. Pressure Piping Code B31 was written to govern the manufacture of pipe. In particular, code B31.1.0 assigns a strength factor of 85% for rolled pipe, 60% for spiral-welded, and 100% efficiency for seamless pipe.

Generally, wider wall thicknesses are produced by the seamless method. However, for the many low-pressure uses of pipe, the continuous welded method is the most economical. Seamless pipe is produced in single- and double-random lengths. Single-random lengths vary from 16′-0″ to 20′-0″ long. Pipe 2″ and below is found in double-random lengths measuring 35′-0″ to 40′-0″ long.

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Recent Developments in Welding Materials for High Performance Arctic Grade Line Pipe Production

R. Vasudevan , ... J.D. Makarchuk , in Pipeline and Energy Plant Piping, 1980

EXPERIMENTAL PROGRAM

Program Design

In essence, the objective of the experimental program was to determine the effect of microstructural modification (by alloy additions to weld metal), welding parameter and flux basicity on the notch toughness of weld metal. In addition to full size charpy tests for notch toughness, hardness survey and metallographic examination of weld metal were conducted.

It should be noted that the results reported in this experimental study are applicable to the welding heat inputs and cooling rates typical of the commercial seam welding practice of line pipe. Caution should be exercised in extrapolating the results to heavier sections, lower-deposition rate techniques or to a different base plate composition. Since the typical dilution is of the order of 60-70% for multi-wire submerged arc welding practice, the base plate composition is very significant in determining the final weld metal composition, microstructure and the resulting notch toughness of the weld metal.

Materials

Two different Mn-Mo-Cb type base materials were employed for the present study, the chemistries of which are given in Table 1 . Plate A is a higher thickness, higher chemistry steel of the X-65 grade to be used for spiral welded pipes. Plate B is a leaner chemistry steel which would meet X-70 requirements after U-O expansion treatment because of its work hardening characteristics. The representative microstructures of the two plates are shown in Fig. 1.

TABLE 1. Composition of Pipe Line Steel Materials

Thickness (mm) C Mn Si S P Mo Ni Cr Cu Cb(Nb) Al
Plate A 18.3 0.06 2.09 0.24 0.009 0.006 0.37 0.24 0.03 0.07 0.05 −
Plate B 16.3 0.06 1.29 0.22 0.004 0.017 0.30 0.10 0.11 0.37 0.013 0.034

Fig. 1. Representative microstructure of base plates 2% nital etch. Mag. 400 diams.

Plate A - Spiral Welded Pipe

Procedure

The base plate joint design is shown in Fig. 2. Since the plate was to be welded spirally, it was important to select only fast freezing fluxes and hence only acidic fluxes (Linde 585 and experimental 585X) were tried. Linde 585 is a highly acidic SiO2-MnO-TiO2 type of flux with a basicity index * of 0.64, whereas 585X is a modified version of 585 flux with a basicity index of 0.86 with its operating characteristics very similar to that of 585. These two fluxes were chosen to see the effect of basicity (and hence oxygen level in the weld metal) on the fracture toughness of welds.

Fig. 2. Base plate joint design for Plate A.

During the initial stage of investigation several alloy wires and combination of wires were tried using 585 flux as a first step to provide a basis for further investigation if need be. During the second stage attempts were made to improve the microstructure (maximum acicular ferritic structure) by adding alloying elements (Mn powder) to the weld metal directly. Addition of Mn to the weld metal was achieved by uniformly distributing electrolytically pure Mn powder (99.5% pure) in the groove before welding. Failure to obtain higher impact values in the second stage led to the third stage of investigation which took on two distinct approaches - (a) trial of leaner wire chemistries with 585 flux, and (b) reduction of oxygen level in weld metal by going to 585X flux.

The welding conditions (for both low and high heat input welds) used during the entire course of this investigation are given in Table 2. The chemistry of various wires used is given in Table 3.

TABLE 2. Welding Conditions Used For Plate A

1.

Regular Heat Input (Low) Welds

Lead: 4 mm dia. 650 Amps 28 Volts)

Trail: 3.2 mm dia. 725 Amps 34 Volts) 16.1 mm/sec

Electrode Stick Out - Lead-38 mm, Trail-32 mm

Electrode Spacing − 16 mm

Heat Input =2.60 KJ/mm
2.

High Heat Input Weld

Lead: 4 mm dia. 750 Amps 34 Volts)

Trail: 3.2 mm dia. 800 Amps 42 Volts) 16.1 mm/sec

Heat Input =3.58 KJ/mm

TABLE 3. Composition of Welding Wires Used

Wire Designation C Mn Si S P Mo Ni
44 0.13 2.25 0.1 Max. 0.02 Max. 0.02 Max. 0.40 0.55
36 0.14 2.0 0.03 0.024 0.017 − −
83 0.10 1.90 0.70 0.02 0.017 0.50 −
81 0.15 1.10 0.25 0.024 0.017 − −
85 0.10 1.35 0.75 0.02 0.010 − −
85A 0.10 1.50 0.75 0.02 0.012 − −
86 0.10 1.65 0.97 0.02 0.010 − −
95 0.06 2.5 0.50 0.02 0.015 − −
29 0.11 1.0 0.45 0.025 0.015 − −
29S 0.11 1.0 0.27 0.024 0.017 − −
40 0.15 2.0 0.03 0.024 0.017 0.53 −
·44B 0.13 2.25 0.1 Max. 0.016 0.02 Max. 0.40 0.55
W18 0.16 0.75 0.15 0.009 0.01 0.15 1.85

Additional experimentation, on the best wire-flux combination, was done to study the effect of higher heat input on the fracture toughness of the weld. The welding conditions for high input welds are also included in Table 2.

After welding, specimens for mechanical testing (charpy V-notch specimens taken at mid-thickness), chemical analysis and metallography were cut out from all the welds. Oxygen analysis and micro-hardness traces were run on some welds.

Plate B - Longitudinal Seam: U-O Pipe

Procedure

The base plate joint design is shown in Fig. 3. The base plates were abutted and tack welded by MIG process using Linde 85 wire before welding by submerged arc process. Most of the experimentation was conducted using Linde 851 flux which has a basicity index of 0.88 with excellent operability. To study the effect of basicity on the impact properties, higher basicity fluxes such as 75B (B. I. = 1.15) and 0091 (B. I. = 1.23) were included in the study, although they cannot be used in pipe welding applications because of their poor operability.

Fig. 3. Base plate joint design for Plate B.

A number of wire combinations were tried in an attempt to meet weld metal impact property requirements of 95 joules at −18°C. Note that for this study the first bead was deposited with three wire AC-AC-AC Scott Connected System, and the second bead was deposited with two wire AC-AC Scott System. Several heat inputs were studied to evaluate its effect on fracture toughness of weld metal. Limited experimentation was conducted using only two-wire welds on both sides. The welding parameters used for the various heat input studies are given in Table 4.

TABLE 4. Welding Conditions Used For Plate B

1. Regular Heat Input
ID Weld - first pass - three wire weld
Lead 4 mm Diameter 1050 A, 32 V ) 16 mm spacing ) 27.5 mm/sec
Middle 4 mm Diameter 950 A, 34 V ) )
Trail 3.2 mm Diameter 600 A, 39 V ) 19 mm spacing )
Heat Input = 3.23 KJ/mm
OP Weld - second pass - two wire weld
Lead 4 mm Diameter 1200 A 35 V ) ) 23.3 mm/sec
Trail 3.2 mm Diameter 800 A, 45 V ) 19m spacing )
Heat Input = 3.35 KJ/mm
Electrode stick-out on all electrodes = 38 mm
The plates are tack welded with 86 wire (MIG) before the first pass.
2. Low Heat Input Welding Conditions
ID Lead 4 mm Diameter 1050 A, 32 V ) 16mm spacing ) 29.6 mm/sec
Middle 4 mm Diameter 950 A, 34 V ) )
Trail 3.2 mm Diameter 600 A, 39 V ) 19 mm spacing )
Heat Input = 3.01 KJ/mm
OD Lead 4 mm Diameter 1100 A, 35 V ) ) 27.5 mm/sec
Trail 3.2 mm Diameter 750 A, 42 V ) 19 mm spacing )
Heat Input =2.56 KJ/mm
3. Modified Low Heat Input
ID Lead 4 mm Diameter 1200 A, 34 V ) 16 mm spacing )
Middle 4 mm Diameter 900 A, 36 V ) ) 27.5 mm/sec
Trail 3.2 mm Diameter 600 A, 42 V ) 19 mm spacing )
Heat Input = 3.58 KJ/mm
OD Lead 4 mm Diameter 1000 A, 35 V ) )
Trail 3.2 mm Diameter 800 A, 45 V ) 19 spacing ) 27.5 mm/sec
Heat Input = 2.58 KJ/mm
4. Two Wire Weld Conditions
ID Lead 4 mm Diameter 1000 A, 35 V ) ) 27.5 mm/sec
Trail 3.2 mm Diameter 800 A, 45 V ) 16 mm spacing )
Heat Input = 2.58 KJ/mm
OD Lead 4 mm Diameter 1000 A, 35 V ) ) 27.5 mm/sec
Trail 3.2 mm Diameter 800 A, 45 V ) 19 spacing )
Heat Input = 2.58 KJ/mm

After welding, specimens for mechanical testing, chemical analysis, metallography, oxygen analysis, and micro-hardness measurements were cut out from the welds. Charpy V-notch specimens were taken from the mid-thickness of the plate with the notch located at the center line of the weld.

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Pipeline Design and Construction

Don D. Ratnayaka , ... K. Michael Johnson , in Water Supply (Sixth Edition), 2009

15.12 Steel Pipe Manufacture and Materials

BS 534 covers carbon steel pipes, joints and specials (bends and other fittings) but is partly replaced by BS EN 10224 (pipe ranging from 26.9 to 2743 mm outside diameter using steel of yield strengths 235, 275 and 355 N/mm2) and by BS EN 10311 for joints. BS EN 10312 covers stainless steel pipe. EN standards have been published and others are under development for polyethylene, galvanized, liquid epoxy and polyurethane coatings, mortar linings and external concrete and insulating coatings, but reference can be made to BS 534 for coatings and linings. BS EN 10224 uses pipe consistent with BS EN 10216-1, 10217-1 and 10220, but pipe to ISO 3183 (API 5L) and other standards can be used. CP 2010 Part 2 for design and construction of steel pipes on land remains current. BS EN 1295-1 covers structural design of buried pipelines for the water industry. Eurocode 3: BS EN 1993-4-3, issued in 2007, applies to design of steel pipelines which are not treated by other European standards covering particular applications; it can be used as soon as its national annex is published. This code requires consideration of 5 ultimate limit states, including fatigue, and three serviceability limit states including vibration. PD 8010-1 and -2 are intended primarily for oil and gas pipelines but apply to and provide useful design information for the water industry.

BS EN 10224 covers four principal welding methods for manufacture: butt (BW)—outside diameter up to 114.3 mm; electric (resistance) welded (EW)—outside diameter up to 610 mm; seamless (S)—outside diameter up to 711 mm and submerged arc welded (SAW)—outside diameter 168.3 to 2743 mm. In ISO 3183 the designations EW and SAW are recognized but seamless pipe is designated SMLS and LW means laser weld.

Steel pipes are fabricated from steel plate bent to a circular form or they may be continuously produced from a coil of steel strip bent to a spiral and butt welded along the spiral seam. Joints between coil ends of spiral welded pipes are known as skelp end welds. Butt welded pipes are made from rolled strip with a longitudinal seam furnace butt welded by a continuous process. Lengths of pipe are usually in the range of 9 to 12 m dependent on manufacture, transport and project requirements. Weld beads must be machined flush with the pipe surface at pipe ends to make them suitable for joint couplings. Spigot and socket ends, where shaped, are formed by die. Weld bead height needs to be limited for coating and lining. Electric (resistance) welding is done by passing electric current (by induction or direct contact) across the edges which are joined under pressure, without filler metal. Heat treatment at least of the weld zone is usual in sizes larger than DN 200. EW pipes now tend to be known as HFI (high frequency induction) pipes. Inspection typically includes chemical and mechanical material tests, ultrasonic inspection of plate and welds, radiography of welds and hydraulic pressure tests.

There are no standard classes for steel pipes: wall thickness above about DN 750 is designed for handling; internal pressure; buckling under external pressure and internal sub-atmospheric pressure; and to limit deflection when buried. External load carrying capacity in trunk mains is mostly a function of the backfill and compaction design. BS 534 sets out nominal wall thicknesses considered to be the minimum for handling and typical buried installations.

Steel grades as designated in ISO 3183 and, as from 2008, the American Petroleum Institute standard API 5L are designated by grade and by yield stress in thousands of psi, as Table 15.3. Grades less than grade B would not normally be used. Grades up to about X60 can normally be welded without special heat treatment. Their price is only marginally above that for grade B and provide good economy where high pressure or (typically for pipes above ground or installed underwater) significant longitudinal bending resistance is required.

Table 15.3. Steel grades to API 5L / ISO 3183

Grade A25 A B X42 X46 X52 X56 X60 X65 X70 X80
Yield strength psi 25 400 30 500 35 500 42 100 46 400 52 200 56 600 60 200 65 300 70 300 80 500
N/mm2 175 210 245 290 320 360 390 415 450 485 555

AWWA M11 gives a range of thicknesses and pressures and steels for diameters up to 4000 mm. Sizes in M11 are designated by outside diameter below 30 inches (762 mm), otherwise by inside diameter.

Pipe wall thickness, t (mm) for internal pressure is determined by hoop stress, as follows:

where P is the internal pressure (N/mm2); D is the external diameter (mm); a is the design or safety factor; σ is the minimum yield stress (N/mm2); and e is the joint factor. The design factor, joint factor and definition of wall thickness depend on the design code. Design factors for hoop stress typically range from 0.4 to 0.8; the joint factor is 1.0 for SAW pipes and certain codes require the negative tolerance to be deducted from wall thickness. ASME codes B31.4 and B31.8 quote a basic design factor of 0.72 and state that this includes for thickness tolerance. For water supply under normal conditions, it is suggested here that the design factor of 0.5 (as given in AWWA M11 and the WRc pipes selection manual) is overly conservative and that, for high pressure long distance pipelines, a factor of 0.72 is realistic (after deducting thickness tolerance and any corrosion allowance) and up to 0.83 may be considered in some circumstances (PD 8010, BS EN 14183). For many water supply pipelines wall thickness is determined by handling and installation and the need to control deflection.

Further consideration can be given where particular conditions warrant: for example the American Society of Mechanical Engineers (ASME) code B31.8 quotes design factors for a variety of laying conditions. Where necessary the analysis can be elaborated to include ring bending, longitudinal bending, longitudinal stress from temperature changes, Poisson's ratio effects on buried (and thus restrained) pipe under hoop tension, combined (equivalent) stresses and where appropriate, for example for underwater pipes, can include strain based design.

BS EN 10224 and BS 534 give dimensions for common fittings, for example bends and branches. However, fittings can be made to any dimensions required, bends being made by cutting and welding together sections of pipe. For outside diameters up to 1016 mm, bends can be made by forming. Design of fittings and of any reinforcement needed is described in AWWA M11.

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