Latest Oil and Gas News Russia

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 

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