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Archive: 01/01/2022

Compressor Inspection in Switzerland

Compressor and pumps are two rotating equipments that carry fluids inside a plant or circuit.

Two of the most common compressor used in industry are centrifugal and reciprocating, depending on the duty they are involved. Also axial compressor and screw are used in some applications.

For testing, exists two reference standards API 617 for centrifugal compressors and API 618 for reciprocating compressors. In both documents there is a dedicated section for inspection requirements, but the client can decide the extention of the inspecting activities.

We as a company have a vast experience with inspecting compressors, both centrifugal and reciprocating whose have some activities in common and some specific for their category. Starting from the very beginning of the construction phase, we assisted hydrostatic pressure test of the casing, that can house the cylinder in case of reciprocating compressor or the impellers in case of centrifugal compressor.

Centrifugal Compressor

Successively overspeed and balancing of the impeller is key step in ensuring compressor performance. Assisting to this step is very important because allows to verify the fundamental frequency of the impeller which is important for maintenance and performance analysis.

After balancing, performance and running test are performed. Performance test scope is to simulate process condition at supplier shop and determine the behaviour in terms of polytropic head and thermodynamic efficiency. To achieve this, there is a sequence of steps to follow in order to get the nearest result of the behaviour compressor can have under process condition.

On the other side, running test scope is to determine reliability/endurance behaviour of the compressor. After completion of both performance and running test, inspection of the bearings is done to verify wearing, scratches that are caused by tests.

Final stage is assembly and final inspection.

Being based in Switzerland, we have the assignment to witness tests from the first step to the final stage, packing

Reciprocating compressor

Reciprocating compressor inspection, starts with hydrostatic test of the casing that will house the cylinders. After hydrostatic, air & helium test are done to fully determine possible leaks.

Performance test is a key step for evaluate compressor behaviour and also cylinder head inspection is needed. In contrast with centrifugal compressor, after running test, piston allignment need to be measured and verify if in tolerance.

Packing is the last activity to do by checking tools and spare parts provision.

Hinkley Point C – Blade construction Inspection

Hinkley Point C nuclear power station (HPC) is a project to construct a 3,200 MWe nuclear power station with two EPR reactors in Somerset, England.

The site was one of eight announced by the British government in 2010 and in November 2012 a nuclear site licence was granted.

Power generation is made by two GE Arabelle nuclear steam turbine. One of the most important components in power generation by turbine is the shape of the blade.

As based a company based in switzerland, we were chosen to follow construction of blade of the 1st stage of the turbine by witnessing forming, welding, NDE and dimensional check.

Finished blades

Blades (airfoils) were made in Switzerland by a Swiss manufacturer specialized in airfoil construction for different applications, ranging from energy production to aviation.

Airfoil is made by shaping two plates, one for high pressure side and another for lower pressure side. After forming, the two halves are welded at the leading edge and trailing edge.

Finally after machining airfoil get his final shape and can be inspected for weld defects, geometrical deviations and surface condition.

Sellafield project – Weld Supervising

After 2 interviews with Sellafield representative our company was involved as Tier 5 on full time basis in supervising weld activities, NDE & FAT testing 5 gate valves intended for HVAC system lifetime operational. The valves were fabricated in Switzerland, Basel area.

Sellafield, located 500 km north London, is the biggest nuclear site in Europe. Covering 265 hectares, comprises 200 nuclear facilities, 1000 buildings and 10.000 employees.

Starting from 2003, nuclear production of power generation was shut down leaving operative facilities for reprocessing or storage of spent nuclear fuel and/or nuclear waste coming from Europe.

The site is due to be fully decommissioned in 2120.

The Project

The Box Encapsulation Plant Delivery Team is an unincorporated joint venture of Amec Foster Wheeler, Balfour Beatty and Jacobs.

The framework contract for the project was awarded in October 2014 and is being delivered as an integral part of the Magnox Swarf Storage Silo (MSSS) programme for Sellafield Ltd, which is tackling the clean-up of one of the most hazardous legacy facilities on the Sellafield site.

When complete BEP will deliver the capability to treat nuclear waste recovered from MSSS, immobilise it and prepare it for storage. In addition, the BEP may also process waste recovered during the decommissioning of other Sellafield facilities including the First Generation Magnox Storage Pond (FGMSP) and the Pile Fuel Storage Pond (PFSP).


After 2 interviews with Sellafield representative our company was involved on full time basis in supervising welding activities, NDE & FAT testing 5 gate valves intended for HVAC system lifetime operational. The valves were fabricated in Switzerland, Basel area.

According to Nuclear QA grading, the valves (or dampers) were classified with a quality grade 2:

Failure is likely to lead to a MAJOR but less serious radiological risk


cause serious injury to persons


lead to a breach of the Site Licence or Environmental or Statutory requirements


lead to SIGNIFICANT cost penalty


The construction of the valve isin 304L, 5 mm plate with metal-to-metal sealing and removable internal mechanic blade.

Welding process was divided in 3 stages to avoid deformation due to high precision required to ensure -0.5 mbar vacuum.

The first stage isthe fit-up; the second stage consist in more than 300 welds seams with different lengths, third stage only minor welds.

The welding process was manual TIG or GTAW with only one approved weld position, having an impact on the handling of the damper with final weight of 350 kg. One of the key parts of welding was the colour of the weld and the grade of inerting/shielding.

First weld layer was monitored in terms of forming gas flow rate, weld seam length (max. 100 mm) and welding parameters. Since back gouging was not practical due to low space, the entire body was sealed and inerted with forming gas. An oximeter was used for monitoring the quantity of oxygen generated during welding.

Surface wet pickling was not practicable due to impossibility to ensure water full dryness so the final surface condition was glassblasted (100 microns glass microsphere). A test was done the verify the removal power of the glass against weld seam colour. It was found that the colour of the welds where the O2 was above 30 ppm, cannot be removed.

After 200 working days all 5 valves were completely welded.

Before testing, cleaning was achieved with solvent; the chemical composition of the pure inlet solvent stream was monitored and compared with the outlet wasted stream. When the difference between clean inlet & outlet contaminants was zero, the damper was considered fully clean.

Testing was aimed to check vacuum tightness with obtained values of zero flow rate passing to the seats.