GERMAN GAS PIPELINE FIRST TO USE NEW GENERATION LINE PIPE

V. Chaudhari, H. P. Ritzmann, G. Wellnitz
Mannesmann Anlagenbau AG
Dusseldorf

H.G. Hillenbrand
Europipe GmbH
Ratingen, Germany

V. Willings
Ruhrgas AG
Essen

Ruhrgas AG, Essen, Germany, in 1992-93 installed a pipeline that used the world's first-ever GRS 550 TM (Grade X-80) line pipe.

This X-80 Grade, specified as GRS 550 TM (TM = thermomechanically treated steel) by Mannesmannroehren-Werke AG (MRW), Muelheim, Germany, has a specified minimum yield stress (SMYS) of Rp (resistance proportional) 0.2 = 550 Newtons/sq mm and a minimum tensile strength of Rm = 690 Newtons/sq mm.

The project, a 163 mile, 48-in. gas pipeline from Schluchtern in Hessen to Werne in North Rhine Westphalia, Germany, connects existing pipelines in new federal states in the former East Germany (Fig. 1) (11629 bytes). The line began operating in late 1993.

Europipe GmbH, Ratingen, Germany, supplied all the line pipe, approximately 145,000 metric tons. MRW, produced for the first time induction bends in this material grade.

Additionally, field welding on the project was carried out by use of a combination of electrode/cellulose electrode for root and hot-pass and of lime-type basic electrodes for filler passes; final layers were by vertical downhill welding.

As a result, the repair rate was less than 3% and thus better than when pure cellulose-coated electrode welding is used.

And by strictly applying the required quality-assurance system according to ISO 9001, Mannesmann Anlagenbau AG (MAB) further reduced defects and deviations.

It thus has a higher design potential than the more widely used X-70 because it allows system design with either thinner wall thicknesses at constant operating pressure or a corresponding increase in operating pressure.

The comparable API 5 L-Grade X-80 has a significantly lower tensile strength - 620 Newtons/sq mm. The German standard DIN 17172/EN 10208 requires, for the higher grades, the higher tensile strength value of the GRS 550 TM with a factor of 1.25 between yield stress and tensile strength.

Use of GRS 550 TM steel in the Schluchtern-Werne pipeline allows Ruhrgas an operating pressure of 1,450 psi, compared to an operating pressure of 1,160 psi for Grade X-70. This level permits considerably more gas to be transported over the same time.

PROJECT CONCEPTION

Ruhrgas AG, a major gas distributor and operator of pipeline links in Germany, has contracted for additional gas deliveries from North Sea fields operated by den norske stats oljeselskap a.s. (Statoil), Stavanger, to cover increasing natural-gas requirements and improve supply independence.

In the new German federal states, moreover, natural-gas demand is growing, especially for ecological reasons to replace brown coal, the primary energy source.

With existing north-south gas-transportation systems running full, a new north-south pipeline system to meet the requirements has become necessary.

Thus, Ruhrgas planned the 163-mile Werne to Schluchtern gas pipeline.

The pipeline had to blend inconspicuously into the countryside of the German Low Mountains. Included in the approval procedure was an environmental protection plan together with details of replacement measures for those areas where sufficient planting could not be provided after construction.

For much of the distance, contracting companies faced a reduced right-of-way (ROW) of from 97 ft to less than 61 ft.

These restrictions required an accurately planned construction schedule for all work cycles from ROW preparation to surface reconsolidation.

MATERIAL, PIPE PROPERTIES

The internationally known steel StE 480.7 TM (API 5L Grade X-70) with an SMYS of Rp 0.2 = 480 Newtons/sq mm and minimum tensile strength of Rm (resistance minimum) = 600 Newtons/sq mm has for years proven efficient in its implementation, design, construction, and operation.

Until now, pipelines with diameters of up to 48 in. and operational pressures up to 1,197 psi have been constructed with this steel in Germany.

Table 1 (7108 bytes) shows how material development in pipeline construction during the last 40 years has tended towards ever greater yield and tensile values with higher toughness properties and processing possibilities.

There are many reports about the development of individual materials, their peculiarities, and the achievement of their specific properties.1-6

MRW began manufacturing pipe of this material in 1985 and 1986. At that time, pipe was supplied for small projects: 3.2 km of 44 in. OD x 0.536 in. W.T. for the central European natural-gas link in southern Germany (Megal II)7 and 1.6 km of 56 in. OD x 0.615 in. W.T. for the natural-gas line through what was then Czechoslovakia."

In 1992, Ruhrgas placed its order for the Schluchtern-Werne pipeline that is under discussion here.

Properties of GRS 550 pipe are shown in Table 2 (15822 bytes).

The base composition of the steel used consists of O.09% C, 1.9% Mn, 0.04% Nb, and 0.02% Ti. Addition of Cu, Ni, or Mo is unnecessary.

The yield and tensile strength values measured on the pipe are shown in Fig. 2 (12885 bytes).

As seen in the figures, the specified minimum values are easily achieved.

The strength values were determined with the use of round-bar tensile specimens because the strain-hardening behavior of the bainitic material leads to a large Bauschinger effect. The higher the strength level, the greater is the Bauschinger effect.

In other words, the proof stress values measured on flattened rectangular specimens taken from the pipe do not correlate well with the actual proof stress values of the pipe wall.

The impact-energy values measured on the base material exceed 95 Joules, thereby exceeding the minimum value for crack arrest recommended by the European Pipe Research Group (EPRG).

The ductile-brittle transition temperatures measured on the drop-weight tear test (DWTT) specimens are well below the specified test temperature of 00 C.

The impact energy values of the longitudinal weld metal measured at 00 C., the commonly specified test temperature in Germany, vary between 100 and 200 J,

The weld metal has a high Mn content and is alloyed with Mo. This weld metal represents an acceptable compromise with respect to toughness and mechanical strength.

The strength of the seam weld was checked by means of flattened transverse weld specimens with the weld reinforcement removed by machining. All specimens broke in the base material, that is, outside the weld region.

Thus, all the measured tensile-strength values reflect the strength of the base material and are greater than the specified minimum value of 690 N/sq mm.

Extensive tests were carried out to determine the welding characteristics of GRS 550 TM and its process-ability in the field.9-12

For field welding, suitable electrodes had to be developed with yield and toughness values analogous to the base material. Electrodes suitable as per the materials development are listed in Table 3 (10856 bytes).

Whereas cellulose-coated electrodes were used for field welds on up to and including StE 480.7 TM, providing sufficient mechanical-technological properties for the welding metal and welding joint, the field-welding concept for GRS 550 TM made new demands on electrode manufacturers and processors.

Finally, it proved necessary to implement a combined manual welding technology using cellulose-coated electrodes for root and hot pass welding and lime coated (basic) electrodes for filler passes and cap pass welding. 13-15

ERECTION; BENDING

The quality system of MAB, Dusseldorf, incorporates the requirement of ISO 9001 as well as the requirements of authority and environmental bodies. Local conditions such as land use, weather, and other relevant parameters are accounted for.

This information has been collected during the development of pipeline construction in the past.

The continuous-laying concept was applied with consistency to pipe laying. Only in such exceptional cases as steep slopes, damp stretches, and highly restricted sections was pipe laid into the pipe trench with a single-pipe laying procedure aided by pulleys, among other assistance.

The procedure was as follows:

The installation plans were checked.
The MAB pipe design construction was developed to determine the necessary number of field bends of the stipulated wall thickness.
An interim stacking arrangement was agreed upon with the pipe transporter because the field bends were to be manufactured on a central bending site.

The longitudinally welded pipe was supplied in 48 in. x 0.721 in. W. T. or 0.764 in. W.T., respectively, polyethylene coated and epoxy lined, steel grade GRS 550 TM, and average length 17.3 in (56.8 ft) and weight up to 10.3 metric tons.

The pipe was picked up at temporary stacking sites some 5 km apart, visually inspected for damage, and accepted.

After excavation, the pipeline right-of-way was surveyed. The pipeline was then laid according to the cold-bending capacity of the pipes, the inductively shaped workshop-supplied bends, and the points of constraint.

Each pipe joint supplied was measured for its exact length. A numbering system established in advance the respective installation points.

The pipe bending list with the respective pipe numbers was handed over to the bending foreman for cold bending. All field bends were performed at a suitable central pipe bending site by a 60-ton pipe bender.

Pipe bending was carried out in 0. 5' steps. Centralized bending at one location was advantageous in that, in view of the terrain, moving the 60-ton bender across the pipeline section became unnecessary.

Consistently high cold-bending quality could be guaranteed by use of a mandril. Every bend was measured after bending and checked for pucker and inadmissible deformations (more than 4%) with the aid of a calibrating pig.

PIPE DELIVERY

Pipe was delivered according to a pipe sequence list either from a pipe stacking area or from the bending site.

The pipes were transported to the ROW section and laid at scheduled and marked locations according to the numbering system. Advance delivery of pipe by at least 5 working days based on a the timetable of the lead welding crew, ensured a trouble-free assembly, taking material availability into account.

The following quality-assurance measures guaranteed compliance with the procedure:

Check of incoming material supplies
Check of temporary stacking: pipes in batch and proper storage of welding electrodes to protect from humidity and temperature changes
Survey of ROW with calibrated measuring instruments
Pipe bending in the field according to survey reports
Controlled bending of the pipe at bending site
Checking for deformations, generation of puckering, dimensional accuracy
Check of operating readiness of pipeline equipment used.

FIELD WELDING

Due to the relatively short laving section length in heavily undulating terrain, manual welding was selected for pipe joint welding.

For this purpose, a vertical downhill welding process with a combination of cellulose-coated and lime-coated (basic) electrodes was developed (Table 4) (9482 bytes).

The welding-procedure specification (WPS) and procedure qualification record (PQR) was established and qualified. It was consistently used on all pipeline sections.

After preheating of the pipe weld seam, the root and hot passes were welded with cellulose-coated electrodes and filler passes and cap layers with lime-coated (basic) electrodes. All welding was by vertical downhill welding technique.

Due to of the different welding characteristic of lime-coated electrodes compared with cellulose electrodes, all welders were required to attend a 2-week welding training session ending in welder qualification.

The selective training measure and the strict field monitoring and supervision of welders resulted in the repair rate of much less than 3%, based on the number of welds.

Here, also, training of both welding supervisors and welders before field use of the welding process and subsequent consistent checks of welding parameters turned out to be essential quality assurance and control measures.

A quality-assurance system prior to field welding, therefore, must include the following:

Appointment and training of supervisors
Welder training and qualification
Evidence of existing welding specifications and procedural qualification
Welders' strict adherance to welding specifications
Welders and other personnel's strict observation of accident prevention and safety regulations.

Advance and mid-assembly metallographic and mechanical-technological tests of weld seams were integral to the quality-assurance system, in accordance with ISO 9001.

Optimization of the individual welding parameters in pretrials was also scheduled. These parameters were confirmed in concurrent supervised welding tests.

The mechanical test results of the various tested weld metals (Table 5) (10790 bytes) were evidence of their acceptability.

During examination of the mechanical properties of the individual welding joints (Table 6) (16714 bytes), however, test version V3 turned out to be insufficient, a fracture having occurred in the weld metal.

A coroborating chemical analysis showed that the composition of the weld metal could not ensure the necessary minimum strength values.

The impact properties in the pretrials and of the site weld tests are shown in Fig. 2 (12885 bytes). All values determined in the ISO V-impact notch tests are greater than the minimum requirement of 45 joules.

While the values of all weld metal show a relatively low dispersal, results from the transition area (fusion line) of welding joints show larger fluctuations.

This is explained by the varying grain structure of parent metal-base material to weld metal per area of fracture, that is, by the fracture line.

In the hardness test in the cap layer of the welding joints examined (Fig. 3) (7855 bytes), the hardness peaks, particularly in the area of heat-affected zone, with values up to and greater than 350 HV, were measured.

Although such hardness values need not yet be considered alarming, the phenomenon must be carefully observed and examined further.

CRITICAL ELEMENT

The welding time is the crucial part of the economic front-end assembly.

It was therefore important to determine the difference in time, if any, between combined manual welding/cellulose-electrodes for root and hot pass/lime-coated electrodes for filler passes and cap layers, and welding which used only cellulose-coated electrodes.

Fig. 4 (7318 bytes) shows the comparison of the times measured.

It is striking that the actual welding times between the two methods are approximately the same for a 48-in. field weld.

Differences occur in the off-times and are caused essentially by the quality-assurance measures in the use of basic or lime-coated electrodes to remove the slag of previous layers by grinding completely.

Although power wire-brushing for pure cellulose electrode welding has frequently been done, it has turned out to be insufficient for combined cellulose/basic electrode welding: flows have been detected in the weld seam after use of powerbrush and made grinding each layer necessary.

In daily operations on the sections, care was the welder's first duty. The maximum daily output of approximately 32 welds was achieved with a crew of 26 welders.

One entire pipeline construction crew had a strength of 65 persons. On average, a length of 1,640 ft of pipeline could be completed in 1 day.

The logically planned pipeline construction allowed the front-assembly welding crew to weld many concentration points which previously were handled by separate tie-in welding crew.

The reduction of the number of tie-in joints moreover allowed an improvement in laying quality. This improvement could be demonstrated by checking laid pipelines for deformations with a calibrated pig (Type PTX Calpig from Pipetronix GmbH, Stutenssee, Germany) or an electronic geometrical pig (as EGP from Rosen Engineering GmbH, Lingen-Ems, Germany).

For either of these instruments, a major portion of the inadmissible (more than 4%) deformations in the pipeline were measured at the beginning of the construction stage in the area of the tie-in welds.

Thus, according to ISO 9001, the required quality assurance and control measures for field-welding may be summarized as follows:

Cleaning of bevels
Preheating of weld bevels as per welding specifications
Checking of preheating temperatures
Selection of welders for root, hot pass, filler, and cap layers
Welding of layers and beads as per welding plan
Control and check of interpass temperatures
Controlled storage of welding consumables in heaters before, during, and after welding
Checks during grinding of individual layers
Visual inspection of the complete welding seam after welding
Covering the welded seam with insulation mats to avoid sudden cooling.

Not following these regulations may result in formation of hydrogen-induced lateral cracks, especially when moisture is not entirely removed before welding, when basic electrodes have been exposed to air humidity and improperly protected in heated containers, or when the secured welding sequence, as specified by the welding plan, has not been observed.

DOWNHILL WELDING

On level terrain, the mechanized orbital welding system may be used as an economic alternative to combined electrode manual welding. 16-19

All necessary preconditions for use of automatic-mechanized GMAW vertical downhill welding by CRC technology were provided (GMAW = gas metal arc welding).

Table 7 (14129 bytes) shows the welding parameters obtained in test series and confirmed in procedural tests for CRC-welding of GRS 550 TM pipes 48 in. OD x 0,717-in. W.T.

Fig. 5 (7905 bytes) shows the outstanding toughness properties ascertained in a Charpy V-notch impact test of a weld metal consisting of GRS 550 TM steel when compared to grades of lower strength.

Achieving the necessary tensile strength properties of at least 690 N/sq mm for GRS 550 TM with the CRC-welding system is also possible.

COATING, LAYING

After successful nondestructive examination with gamma ray and ultrasonic testing of the welding seams, the welding seams were coated with a three-layer anticorrosion system and the polyethylene (PE) pipe coating and was checked for anticorrosion protection with a test voltage of 20,000 v.

The pipe sections were lowered with the aid of seven lateral-boom crawler-tracked cranes (lifting force 90 metric tons) onto the previously prepared trench sole (Fig. 6) (7150 bytes). All pipe ends were deposited on sand barriers or sandbags and not on stacking timber as had been customary.

In rocky soil, the ditch must be deep enough to allow sufficient covering with sandy soil and the additional layer of necessary minimum soil covering.

For this purpose, the necessary trench recesses were marked directly on the spot and visible to the excavator operator. These marks were made either on the pipe or at the edge of the ditch section using signboards on the mother soil banquette at the ROW edge.

For completion of the pipe trench, drilling and blasting equipment was used in some long sections. After blasting, the pipe trench sole was mechanically smoothed with a low-power trench caterpillar.

Where necessary, a continuous sand soil at least 20 cm thick was put in so that the pipe could be positioned as evenly as possible along the entire pipe trench sole and concentrated support points would be avoided.

Immediately after lowering, the pipe sections were joined. The tie-in welding joint was brought into position with four lateral-boom crawler-tracked cranes and welded by two or four welders, respectively. Every two welders completed an average of 1.5 welds/day.

The pipe section was filled with stone-free material up to the abutment. The filling material was specially compacted with mechanical equipment (jolting table) only in areas of roads and crossings.

Care was taken to ensure that no cavities would remain in 4 to 5 o'clock and in 7 to 8 o'clock positions. For soils with portions of stone-free material, the degree of compacting provided by bulk compaction is normally sufficient because a high degree of compacting is obtained from subsequent construction works.

After completion of the cable sole in a 2 o'clock position, the control cable or cable-protection pipe in which the control cable was subsequently laid was put into place. After this operation, the pipeline was covered with stone-free material to a minimum layer thickness of 20 cm.

The high penetration resistance of the PE-pipe coating enabled use of 0-25 mm grain diameter for the embedding material.

In portions, the embedding material was produced directly from the excavated soil with a self-operating and self-loading sifting screen and installed directly. In the area of the welding seam coating, however, the pipeline was embedded only with materials having a grain diameter of 0-8 mm or additionally protected with rock matting.

The embedding material was compressed with excavator shovels and the trench then filled with excavated materials or with exchanged soil at a camber.

The excavated material was deposited adjacent to the trench. This material was analyzed to ascertain its suitability for the padding-layer under the pipe. Unsuitable material such as blasted rock was rejected.

As a result, sufficient material was available at the point of pipe lowering regardless of weather or transport capacity. It was always possible, therefore, to ensure pipe trench filling immediately after pipe was lowered.

HYDROSTATIC TESTING

The pipe sections were hydrostaticaly tested per VdTUV Guideline 1060 in length up to 100 m (328 ft), corresponding to a volume of 6,000 cu m of water. The height difference within the test sections, material grade, and the wall thicknesses must be considered.

Before filling for the hydrostatic pressure test, the water quality was checked for corrosiveness.

At the lowest point of the pressure-test section, the pipes were tested up to 108% of the specified minimum yield strength (SMYS).

Dry pigging of the pressure-test sections was performed with a pig which was equipped with an aluminum calibration disk with a diameter of 98% of the pipe ID.

It thus became initially possible to demonstrate the absence of bulging, as specified in the contract (per DVGW Worksheet G 463, July 1989) with the pipeline owner.

Therefore, an automated geometrical measuring system using a PTX Calpig or EGP pig was chosen for the Ruhrgas pipeline.

Recording the ID measurements revealed that the laying quality of the pipeline, regardless of the degree of difficulty of the terrain and in spite of the permitted low ovalities in parts (less than 2.2%), was so high that no inadmissible deformation was detected.

Additionally, over a construction length of 113 km laid by Mannesmann Anlagenbau AG, only a single ovality of more than 4% was found.

Evaluation of the deformations, including those smaller than 4%, assumed the following causes:

Additional ovality in field bends with permissible ovalities from additional loads (the pipe's annular strength was reduced by the ovality)
Laying stress during the completion of tie-in-welds of two lowered pipe sections
Different degree of compaction in the pipe trench sole
Resting on rock banks in spite of embedding in stone-free material.

Generally in this project, after comprehensive inspection of the causes of deformation following construction of the first two sections, detailed measures for quality improvements to laying technology were drawn up with the owner, engineer, expert, and contractors.

The result was that the 48-in. Werne-Schluchtern pipeline through the Low Mountains of Germany was laid to the highest quality.

REFERENCES

Peters, P.A., Graf, M.K., and von Hagen, I.J., "Microstructure and Mechanical Properties of Thermomechancially Rolled and Accelerated Cooled Line Pipe Steels," 5th Biennial joint Technical Meeting on Line Pipe Research (EPRG), Sept. 27-28, 1983, San Francisco.
Graf, M.K., Lorenz, F.K., Peters, P.A., and Schwaab, P., "Relationship between Microstructure and Mechanical Properties of Thermomechanically Treated Large-Diameter Pipe Steels," 1983 International Conference on Technology and Applications of High Strength Low Alloy (HSLA) Steels (in conjunction with 1983 Metals Congress), Philadelphia, Oct. 3-6, 1983.
Hof, W.M., Graf, M.K., Hillenbrand, H.C., Hoh, B., and Peters, P.A., "New High-Strength Large-Diameter Pipe Steels," CSM Conference: HSLA Steels '85, Peking.
Junker, G., Maxey, W.A., Peters, P.A., and Vogt, G., "Transition Temperature Determination on Large-Diameter High-Toughness Pipes of Grade X80," Special reprint from 3R International, Vol. 25 (1980), Ease. 4, pp. 178-182.
Gartner, A.W., and Peters, P.A., "Line Pipe-A Producers View of the Year 2000," 7th Symposium on Line Pipe Research (AGA), October 1986, Houston.
Buzzichelli, G., Fearnehough, G., Nicolazzo, F., Re, G., Venzi, S., and Vogt, G., "Full-Scale Gas Transmission Pipeline Fracture Tests with Thick Wall Pipes and Pipes of Grade X80," Special reprint from 3R International, Vol. 26 (1987), Fasc. 3/87, pp. 177-183.
Engelmann, H., Engel, A., Peters, P.A., Duren, C., and Musch, H., "First Use of Large-Diameter Pipes of the Steel GRS 550 TM (X80)," Special reprint from 3R International, Vol. 25. (1986), Ease. 4/86, pp. 182-193,
Matouszu, M., Skarda, Z., Beder, I., Lombardini, J., Schuster, H.G., and Duren, C., "Large Diameter Pipes of Steel GRS 550 TM (X80) in the 4th Transit Gas Pipeline in Czechoslovakia, 3R International, Vol. 26 (1987), No. 8, pp. 534-543.
Duren, C., "Equations for the Prediction of Cold Cracking Resistance in Field-Welding Large Diameter Pipes," 3R International, Vol. 24 (1985), No. 8, pp. 434-439.
Duren, C. F., "The Mannesmann X80 Concept and Girth Welding Tests," Mannesmann-Sonder-drucke.
Laing, B.S., "PGMAW Welding of X80 Pipe," Offshore Pipeline Technology Conference, Paris, February 1990.
Duren, C.F., Korkhaus, J., and Niederhoff, K., "Field Welding of Large-Diameter Pipes of Steel X80 and ME GRS 550 TMT."
Perteneder, E., Konigshofer, H., and Mlekusch, J., "On the Present State of Field Welding of Pipelines by Means of Covered Electrodes," International Pipeline Technology Conference, Oostende (Belgium), Oct. 15-18, 1990.
Perteneder, E., Konigshofer, H., and Mlekusch, J., "Contribution to the Present State of Field Welding of Large-Diameter pipes using Electrodes," DVS 146 (1992).
Dittrich, S., "First Construction of a Complete X80 Gas Pipeline by Using the Downhill Welding Process with Coated Electrodes," Doc. IIW Sc. XI-E 19/92.
Musch, H., Chaudhari, V., Hess, H., and Wellnitz, G., "Field Welding of Pipelines for Sour Gas Application," 3R International, Vol. 29 (1990), No. 6, pp. 332-338.
Dittrich, S., "Newest Experiences on Shielded Metal Arc Welding of Grade X80 Pipes," 23rd Annual Offshore Technology Conference (SPE), Houston, May 6-9, 1991, pp. 339-406.
Gawlick, S., Hauck, G., Kiewel, G., and Sandner, G., "Automatic Inert Gas Welding on the X80 Werne-Wetter Ruhrgas Pipeline using the CRC-Procedure," DVS 155.
Selling, R., Hauertmann, J., and Dehning, H., "Automatic Welding in Pipeline Construction," 3R International, Volume 32 (1993), No. 8, pp. 450-454.

THE AUTHORS

Vinayak Chaudhari is a welding engineer and project quality-assurance manager for major projects with Mannesmann Anlagenbau AG, Dusseldorf, an engineering and construction company. He holds a BS in engineering, process technology, from the College of Engineering, Krefeld, Germany, and is a certified welding engineer of the German Welding Associations College, Duisburg. He is a member of AWS, DVS, and VDI.

Hans-Peter Ritzmann is a project manager for pipeline construction with Mannesmann Anlagenbau AG. He holds a BS in mechanical engineering from Technical College, Hannover.

Hans-Georg Hillenbrand is a senior manager and head of technical service of Europipe GmbH, Ratingen, Germany. He holds an MS in mechanical engineering and a PhD in engineering, both from Aachen University, Germany.

Gerhard Wellnitz is a director and responsible for corporate quality assurance of Mannesmann Anlagenbau AG. He holds an MS in engineering metallurgy and a PhD in engineering, both from Aachen University, Germany.

Volker Willings is head of projects management for Ruhrgas AG, Essen. He holds a diploma (1970) in mechanical engineering from Technical College of Mechanical Engineering, Essen.