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R.V. LUGUMANOV, V.P. YATSENKO

PROCEDURE AND ORGANIZATION OF WELDING AND ASSEMBLY WORK
The number of welds made during construction of the line part of the oil pipeline was as follows:
by manual arc welding (WPS-01 and -02 procedures) 4,730 joints of 30" pipes with wall thicknesses of 11.08 and 13.03 mm at an average daily rate of 0.9 to 1.2 km; by CRC AW automatic welding (WPS-13 procedure) 4,194 joints of 30" pipes with a wall thickness of 11.08 mm at an average daily rate of 1.5 to 1.9 km.

During seam overhead welding according to procedure WPS-01, the pipe joint was assembled on an internal self-propelled pneumatic lineup clamp with a clearance of 1.6-2 mm. Wedges were used to maintain the clearance during the joint assembly and welding process. The root layer of the joint was applied by two welders in approximately 9 minutes. Welding was done on straight polarity, which increased penetration of the pipe edges and welding speed. Electrode travel in the groove was downhill, resting the sleeve of the coating on the joint edges and forming a keyhole under the arc in the molten pool.

In the vertical part of the joint, when the molten metal and slag begin to flow under the arc, the welding current and travel speed were increased. In the overhead part of the joint, the welding current was reduced in order to reduce the weight of the molten pool and improve the formation of a reverse bead.

During the welding process, the welder also kept an eye out for any shift in the edges or change in the joint opening. If the edges shifted, the arc was directed at the farther edge and the electrode tilted toward the joint plane. At the same time, the welder watched out for any burnoff of the closer edge in order to prevent a lack of root penetration. The start-to-finish segments after each electrode were notched with a grinder and abrasive disk. The Indian welders, who were the most experienced, mostly did no notching, and after replacing the electrode continued welding. After the welding, mechanics flushed the joint perimeter, opening up the slag pockets.
Applying the second layer - the hot pass - is the most complex operation in welding with cellulosic electrodes. When applying the hot pass, Russian welders frequently use the wrong method - holding the electrode down without manipulating the end. Doing this requires that the root layer be thoroughly ground, which makes it thinner and thus results in the likelihood of burn-through of the root bead and an increase in the specified interval between the root pass and the hot pass of more than 5 minutes. This leads to reduced diffusion of atomic hydrogen out of the seam and the danger of cracks appearing. The correct way to do the hot pass is by a whipping motion of the electrode tip so that slag is swept out of the pockets. In addition, the welding current source should be set for a steeper volt-ampere curve while keeping the welding current at maximum (in accordance with WPS-01).



The fill layers of the weld were deposited using 4.0mm diameter Fox BVD 85 electrodes for vertical down welding. During the welding process, the arc length should be as short as possible due to the increased tendency to form pores, including start and stop pores. The electrode tip is weaved from side to side in a zig-zag motion without increasing the arc length where the direction changes at the edge of the joint. The missing fill in the groove on the vertical sections of the joint (10-8 and 2-4 hrs of the perimeter) is completed with a final (correcting) fill layer so that it is flush with the pipe edges. On the remaining sections of the joint perimeter just before the face layer is applied, the groove should be unfilled for approximately 0.5-1.0 mm to the pipe edges.

The face layer of the seam is deposited with the welding current set at 20-30 amp less than that used for the fill passes. The width of lateral oscillation of the electrode should not be more than twice its diameter. The width of the layer should be 3-4 mm greater than the width of the groove after the fill layers have been deposited. To avoid undercuts along the edges in the overhead position, the lateral oscillations of the electrode tip should preferably be U-shaped instead of zig-zag. With this welding technique the arc length must be kept as short as possible to avoid pores forming in the overhead position due to insufficient arc protection. For joining pipes with wall thicknesses greater than 15 mm, it is advisable to apply the face layer in two parallel beads.

The actual rate of seam overhead welding using the WPS-01 procedure was 15-20 minutes per joint. The overhead team consisted of 10 welders working simultaneously in 5 welding tents:

• Tent 1 - root pass, average welding time 9 min;
• Tent 2 - hot pass, average welding time 4 min;
• Tent 3 - fill pass, average welding time 12 min;
• Tent 4 - fill pass, average welding time 11 min;
• Tent 5 - face pass, average welding time 13 min.

The supply sources used were 2-station and 4-station Arcotrac and Liebherr welding tractors fitted with Lincoln DC-400 welding rectifiers.

For the CRC AW automatic welding (WPS-13 procedure) there were 11 welding operators: one for the internal welding heads and 10 for the external welding heads. They worked in five tents:

• Tent 1 - hot pass;
• Tent 2 - 1st fill pass;
• Tent 3 - 2nd fill pass;
• Tent 4 - face pass;
• Tent 5 - face pass.

In line with the procedure requirements, before being welded the pipe ends were cut with hydraulically-driven circular cross-saws to obtain a special, narrow-gap two-sided bevel. This operation was done by a team using two circular cross-saws with hydraulic stations on the pipelayers. The guide belts for moving the welding heads along the pipe joints were mounted by the following team.

The head team of the welding column assembled the pipe joints (with no clearance) on an internal pneumatic self-propelled lineup clamp combined with a welding machine that welded the root layer of the joint from inside the pipe using six welding heads. The remaining teams welded the outside layers inside the tents listed above using external welding heads and solid-section 0.9 mm diameter wire. The root and face layers were applied in a shield gas mixture of argon + carbon dioxide (75% + 25%), and the hot pass and fill layers in carbon dioxide (100%). All the layers were welded downhill. The system comprised one 4-station (Liebherr) and five 2-station (Arcotrac) welding tractors with hydraulic boom manipulators from which the welding tents were suspended.

Welding of lap joints, taper joints and line valve assemblies was done according to procedures WPS-02 and WPS-03 using external lineup clamps. The joints were assembled using rigid external lineup clamps manufactured by CRC Evans and break-over lineup clamps produced by Russian manufacturers. Experience showed that the CRC Evans clamps were better at eliminating the height difference of the pipe edges in the joint since they use a hydraulic jack. The drawbacks of these clamps are their considerable weight, the difficulty of depositing the root layer around 50% of the perimeter before the clamp is removed, and their high cost compared with Russian-made external lineup clamps.

The pipe joints were assembled with a clearance of 2.5-3 mm. For applying the root layer, 3.2 mm diameter electrodes were used. The welding direction was from bottom to top - uphill. Polarity was straight for welding with cellulosic electrodes and reverse when using basic-coating electrodes. Two welders working at the same time apply about 50% of the root layer perimeter on the external lineup clamp, after which the clamp is removed and welding of the remaining 50% is completed, making sure to notch the start-finish sections.

One of the important factors in welding these kinds of joints is to maintain the preheat temperature. The method traditionally used in pipeline construction whereby the joint is preheated until the external lineup clamp is fitted leads to a drop in the preheat temperature at the start of welding the root layer (to below 80-1000C) and consequently to the likelihood of cracks appearing. To eliminate this drawback, the diameter of the collar burners was increased so that preheating could be done after assembly with the external lineup clamp in place on the pipe joint. The fill and face layers were welded downhill with basic-coating electrodes according to the WPS-01 procedure or uphill according to the traditional WPS-23 procedure.

Lap joints were removed by teams consisting of two pipelayer operators, a welding tractor operator, two welders, a gas cutter, foreman, and a rigger. Lightweight fan-type tents developed by Russian specialists from their experience of earlier projects were used to protect weld areas.

Installation of surge relief stations on the existing SHBAB-1 oil pipeline was carried out without halting the oil flow by means of hot taps - welding split tees to the oil pipeline and then tying in safety valve stations using TD Williamson equipment.

Welding of split tees for hot taps was done using the WPS -10, -11 and -12 procedures. The members of the split tee were mounted onto the operating pipeline at the tie-in point and held in place on the pipe by two break-over external lineup clamps. First, two horizontal seams were welded to join the two members of the tee into a single structure. Welding was done with beads using the step-back method. The clamps were allowed to be removed after 25% of the cross-section of the horizontal seams had been welded. After the horizontal seams were welded, circular fillet welds were made to join the tee to the pipeline. Welding was done from the bottom up with separate beads using the step-back method by two welders at the same time. The anchor flanges were welded in the same way.

Defects were removed using the WPS-03 and -28 procedures by repair teams consisting of an experienced welder and a welding tractor operator.

According to client specifications, a repeat repair was permitted one time.

Repairs were made both outside and inside the pipeline. The defects were marked out by the repair team using a measuring band (similar to the bands used by defect detector operators). The defects were ground with abrasive disks. For repairing a root layer from the outside, abrasive disks 2.2 mm thick were used for a section that was to be cut through, and for all other cases the thickness was 4 and 6 mm. Grinding of the defects was generally done by the welding tractor operator, but if a through cut was required, it was done by the repair welder with a hacksaw to obtain an even opening of 2.5 - 3 mm.

To reduce the likelihood of cracks appearing during repair of the root layer of lap joints, the following sequence of process operations was used in the project:

• preheat the joint to be repaired using a propane collar burner to 120 - 150 0C;
• remove the defective section;
• reheat the joint again, immediately before welding, to 120 - 150 0C;
• weld the defective section while strictly maintaining the interpass temperature;
• when welding is done, put a thermal wrap around the joint to reduce the cooling rate.

When the root layer of lap joints was repaired in the above sequence, there were ultimately no cracks.

Of great practical interest here was the welding process monitoring procedure that was developed in line with the quality management system and used in the project.

At the preparatory stage it is verified that:

• the relevant (approved) welding procedure is available;
• the pipes meet project requirements and the specifications, and that they are free of unacceptable defects;
• welders and welding operators have the appropriate (unexpired) certification;
• welders are properly equipped (coveralls, boots, leggings, mask, electrode holder, electrode case);
• the equipment and tools are available and in working condition (correct lineup clamp, clearance wedges, electric grinders, return lead clamp, welding protection tents, welding cable, welding current remote control, grounding at end of welded pipeline string, pipe rollers);
• the beveling of the pipe ends matches, including geometry;
• the joint is correctly assembled, including fulfillment of requirements regarding the offset of factory-welded seams and their location;
• the equipment for preheating the pipe ends is in good working order;
• welding materials are prepared (baked) and that they have certificates;
• the welding machines are in good working order.

During the welding process the following are monitored:

• size of the root opening and the amount that it changes during the root pass;
• use of no less than two welders simultaneously for welding pipes more than 12" in diameter;
• removal (release) of the lineup clamp;
• interval between completion of the root layer and start of the hot pass when using an internal lineup clamp;
• the welding current;
• quality of cleaning of each pass;
• that welding is performed in line with the specified procedure;
• absence of arc striking on the body of the pipes;
• completion of the prescribed number of passes;
• interpass temperature meets requirements;
• use of thermal wraps.
• When the welding is completed it is checked for seam geometry and absence of visible unacceptable defects. The edge misalignment is measured and the weld is inspected to make sure that it has been cleaned of slag and molten metal spatter, and that it has been appropriately marked.

The final operations at the end of the work shift are to cap off open sections of the pipeline, complete welding of the face layer on all the welded joints, verify the number of remaining electrodes, and clear away any foreign objects from the production area.

WELDING QUALITY CONTROL AND BASIC DEFECTS IN WELDED JOINTS
Welding quality control was subcontracted to Vetco, a local company that used gamma defect detectors and X-ray machines, including self-propelled pipeline crawlers for internal pipe inspection. The fillet and horizontal welds on the split tees were inspected using powder magnetography and dye penetrant examination. The average percentage of seam overhead joints inspected was 10% of the total number welded, but the overhead joints welded by the CRC AW automatic welding machine were 100% inspected using a Pipewizard automatic ultrasound computer system made in Canada. The inspections were performed by Stroytransgas engineers.

In pipeline construction practice outside Russia, welding quality is generally assessed based on the percentage of unacceptable defects out of the total number of joints:

• up to 5% is excellent quality;
• up to 7% is good quality;
• up to 9% is satisfactory;
• more than 10% is unsatisfactory.

At the facility that was built, repairs were made to 155 joints that had been welded on the CRC AW automatic welder, and to 410 manually welded joints. The total percentage of repair was 6.33%, including 8.6% for manual welding and 3.7% for automatic. Applying the international assessment criteria it can be stated that the quality of manual welding operations was good, and automatic welding excellent.

These levels were achieved thanks to constant monitoring by the office of the project's chief welding engineer, analysis of the causes of the weld joint defects, and determination of the methods to remedy them.

The results of this work are summed up in Table 1, which shows the typical defects encountered in manual arc welding on the project, their causes, and their remedies.



Rasil Varisovich LUGUMANOV, Chief Welding Engineer of the project's construction department in the Kingdom of Saudi Arabia

Vladimir Petrovich YATSENKO, Acting Deputy Chief of the Construction Technologies Department, chief welding engineer of Stroytransgas, PhD

Labels: pipeline welding, Russia, SHAB-1, stroytransgaz

posted by The Rogtec Team @ 17:27  0 Comments

R.V. LUGUMANOV, V.P. YATSENKO

The welding of pipelines, like all other kinds of metal structures, is a fundamental, key process that determines the warranty strength, bearing capacity, and operating reliability of the facilities being built. This is why welding operations in the construction of pipelines and related facilities are governed by special international and national standards and codes. Welding engineering specialists, semi-automatic and manual arc welders, and welding machine operators have to be certified by national welding associations or committees.

For each specific project, the contractor's certified welding experts will draw up the welding procedures (preliminary welding procedure specifications - pWPS) that are prescribed by the technical design specifications. Once these procedures have been approved by the client's welding specialists and/or independent experts, the contractor may begin to have them certified. This involves making qualification weld joints on pipes or metal structures at an assembly site on the actual pipeline route or in near as possible conditions using the welding and assembly equipment that the contractor plans to use on the project in the presence of the client's engineers and independent experts brought in by the client. The welding results are drawn up in a report. After positive results have been obtained from nondestructive testing in accordance with the design technical specification, coupon samples are cut out of the qualification welds for mechanical testing attended by the client's engineers at an independent laboratory recommended or approved by the client. If the test results are positive, appropriate reports are drawn up and the client issues written permission for the certified welding procedure to be used.


CRC AW welding line

The SHBAB-1 project in the Kingdom of Saudi Arabia to increase the capacity of the Sheiba-Abqaiq pipeline includes construction of the 217-kilometer SHBAB-2 oil pipeline made of 30" X65 pipe, pig receivers and launchers, and five line valve assemblies, as well as the installation of 21 pressure surge relief stations and 2 chemical injection units on the existing 42" SHBAB-1 oil pipeline. It is an EPC contract.

Before international bidding on the SHBAB-1 project was opened, all applicants to build the facility were sent tender documents for them to prepare their technical and commercial bids. These documents included preliminary specifications for the performance of all types of work (Saudi Aramco document 2616 ENG 03/99). The performance and inspection of welding and assembly work were additionally governed by the standards of the client itself - the Saudi Arabian oil company Saudi Aramco:

SAES-W-011. Process pipeline welding requirements;
SAES-W-012. Pipeline welding requirements;
SAEP-352. Review and approval of welding procedures.

In addition, there were international standards - for welding pipelines and related facilities (API-1104); pipeline transportation systems for liquids - hydrocarbons, liquefied petroleum gas, anhydrous ammonia, and alcohol (ASME B31.4); and a standard for welder and welding procedure certification (ASME Section IX).

During preparation of the technical and commercial bid on the SHBAB-2 pipeline, experts in the construction technologies department of Stroytransgas carefully analyzed and studied all the construction requirements and then prepared the materials for the bid to be put together.

When the contract was awarded to Stroytransgas, company specialists selected the welding techniques and developed preliminary welding procedure specifications (pWPS) that would meet the procedures and requirements of the client's SAES-W-011 and SAES-W-012 Standards.

Here, special attention was given to the client's procedures and restrictions regarding the use of welding methods and welding materials that are non-typical for pipeline construction. For example, the client's specifications require pipes less than 1" in diameter and the root layer of joints in pipes less than 2" in diameter to be welded only by gas tungsten arc welding (GTAW) with a filler. Gas-shielded arc welding and powder wire welding cannot be used for the root layer in pipe joints and corner joints, and filler metal containing 0.5% molybdenum may not be used in the metal deposit.


Welding the outer layers on a CRC AW welder

The use of cellulosic electrodes is allowed only for welding the root layer of pipe joints.

Any deviations from these procedures and restrictions, particularly the use of automatic gas metal arc welding (GMAW) followed by mandatory weld quality testing with automatic ultrasound equipment, or the use of powder wire welding, required the client's special permission.

The welding procedures and their certification reports were to be completed on a form recommended by the client. Weld joints for steel pipes of strength class X70 and above for operation in sulfur environments were to be tested for stress corrosion cracking. During assembly and overhead welding of the pipeline, until completion of the hot pass weld, the pipe had to be held by the pipelayer boom, which was not allowed to be manipulated. This restriction considerably slowed the pace of the overhead welding. However, it was permitted to do a second defect repair of the welded joints. It was also permissible to reduce the volume of radiographic testing to 10% provided the defect level was low, which was calculated using a special formula in the SAES-W-012 Standard.

While drawing up welding procedures, the contractor was required to use the client's recommended form to compile a summary table of weld joints, listing and grouping by diameter and wall thickness all the pipelines included in the project. This had to show for each group the method and type of welding and the welding materials planned to be used, it had to define the group of materials according to ASME Section IX, and indicate the hardness tests, impact strength tests, and any required post weld heat treatment of the seams that were specified in SAES-W-012.

For all welding operations on the project, 14 preliminary welding procedures were developed and submitted to the client.

For seam overhead welding of pipes into strings on the pipeline route, two techniques were used:

• automatic welding using a CRC AW equipment system (welding with solid section wire in a gas shield of argon+carbon dioxide and carbon dioxide), AWS classification - GMAW (gas metal arc welding);
• high-speed manual arc welding (the root layer and hot pass were deposited with cellulosic electrodes, as specified in SAES-W-012, while the fill and face layers were welded downhill using basic-coating electrodes, AWS classification - SMAW (shielded metal arc welding). This technique resulted in 10-20% greater productivity compared with welding the entire joint using cellulosic electrodes and provided the advantages of the inline-separate method of operation.

For welding lap and taper joints, where an external lineup clamp was used, a combined high-speed procedure pWPS-2 was developed that, in welding the root layer from the bottom up with cellulosic electrodes in straight polarity, assured penetration and formation of a reverse bead. The fill and face layers were welded from the top down using basic-coating electrodes, which was 50-70% more productive than the bottom-up method. The traditional welding technique for these joints, where all layers are welded from the bottom up, was also suggested.

The technique proposed for repairing weld joint defects was the same as that for lap welding.
Other procedures were developed for welding the line valve assemblies, pig launchers and receivers, welding on anchor flanges and split tees, and tying in nipples.

A list of all the welding procedures used in the project is shown in Table 1.

WELDING PROCEDURE CERTIFICATION
The pWPS draft procedures were sent to the client for approval. At the same time, Stroytransgas welding specialists held technical meetings with the client's weld engineering department to decide the major issues regarding compilation and formalizing of pWPS procedures and the procedure for certifying welding procedures. Their approval meant permission for the certification to go ahead.

The certification process for each procedure involved performing certification weld joints, nondestructive testing of the welds and, if the results were positive, mechanical tests on coupon samples taken from the joints.

The qualification joints were assembled and welded on segments of piping supplied for the pipeline construction using the equipment, rigging, and tools that Stroytransgas planned to use on the project. Welding was performed by the contractor's welders in the presence of the client's inspectors.

During the welding process, the following were measured and recorded in the report: the bevel (angle), opening, quality of assembly, preheat and interpass temperatures, travel speed, the time taken for each pass and the interval between passes, welding current, voltage, and the polarity and baking temperature of the electrodes (only with basic coating). After the welding was done, the geometry of the weld seam was measured and, after its external appearance had been accepted by the client, the weld joint was marked appropriately. After this, the certification joints were examined by radiography and, if the results were positive, templates were cut out (in accordance with the chart in Standard API 1104) for subsequent mechanical tests.

The mechanical tests were performed in a client-approved laboratory. After the tests were complete, a document package was put together including: the qualification welding data records, inspection and test reports, certificates for the welded pipes and welding materials, welder certificates, etc. The final stage of certification was a modification to the WPS (flow charts) in line with the actual qualification welding data and their approval by the client.

An item of practical interest was the procedure for certifying weld defect repair procedures, for which there was no real clarity in the client's specifications or Standard API 1104. For this type of repair, pipe joints were used that had been welded according to the certified procedures and in which defects in the root, fill, and face layers of the weld were simulated by grinding segments 250-300 mm long to various depths (completely through, to mid-section, and removal of the facing). These segments were then welded by manual arc welding using proposed procedures WPS-03 and -28. The control procedure during the welding process and subsequent operations was the same as for certification of the basic welding techniques (marking, nondestructive testing, removing coupon samples, mechanical testing, and issuing reports).

For automatic welding on the CRC AW equipment, the client required, in addition to certification of the basic welding procedure, that (as an exception) its modification also be certified - the so-called "overnight procedure". Essentially, this procedure boiled down to the following: qualification pipe joints were welded with a root, hot pass, and two fill passes. After being left for 24 hours, the qualification weld was completed with a fill pass (the third) and face pass. This procedure for CRC AW automatic welding meant that some of the unfinished welds that were missing the final fill and face pass could be left for the next work shift.

WELDER AND WELDING OPERATOR CERTIFICATION
This certification was carried out in line with the above welding standards but with no mechanical testing of specimens from the qualification welds. To obtain a permit to perform overhead welding of pipes, the welder welded half of a non-rotating joint using the certified procedure. The qualification joint was examined by radiography, and if it passed, the welder would be given a welding permit and personal name tag.

To handle the welding operations, the construction department at the facility brought in welders from Russian, India, and the Philippines.

Foreign welders were brought in because of the Saudi Arabian quotas for foreign labor and because of the lower cost of their services compared to Russian welders.

For certifying the welding procedures and welders, Stroytransgas set up a certification area in the production center of the facility's construction department which contained 10 welding booths and was fitted out with everything required to cut spools from the pipe and to assemble and weld the joints. Since the project was to use new high-speed manual arc welding techniques (WPS-01, -02, and -03) that were unfamiliar to most of the welders, a 5-12 day training session was given before the certification tests. In addition, some of the Russian welders had received 5-10 days' training at the YuzhTrubVodStroy training center just before being sent to this job assignment. Altogether during the project 39 welders were trained and certified, 29 of whom were Russian specialists.

Certification of the CRC operators was carried out without preliminary training because they all had extensive work experience. Later on, the client allowed the operators to be certified on actual fabrication joints.

The top-qualified welders who had proved themselves in welding line joints on the trunk oil pipeline were chosen to do the welding of in-service hot taps (welding split tees to an existing oil pipeline). Their certification was carried out on a specially fabricated stand with a device simulating pressurized oil in close to real conditions. Welders who passed this test were given a special certificate.

In addition to primary certification, the test area was also used to train and carry out re-certification testing for welders who had been rejected by the client's inspectors. The client's requirements were that welders whose weld joints requiring repair exceeded 5% of the total number done were to be taken off the job and sent for training and re-certification.

Labels: oil gas, pipeline welding, Russia, SHBAB-1 Project

posted by The Rogtec Team @ 16:16  0 Comments