SEMT Pielstick

SEMT was a French company specialized in the design and construction of diesel engines until 2006 and is now operated as a brand by MAN Diesel and Turbo and its licensees. The full name was Société d’Etudes des Machines Thermiques or Company of Thermal Machines Studies in English.


In 2016, S.E.M.T. Pielstick celebrated its 70th birthday.

S.E.M.T. was created in 1946 by France's ministry for industrial production with the support of five national companies: Société des chantiers et ateliers de Penhoët (Saint-Nazaire), Société Générale de Construction Mécaniques (La Courneuve), Société des chantiers et ateliers Augustin Normand (Le Havre), Société des Ateliers et Chantiers de Bretagne (Nantes), and Société des aciéries du Nord (Denain). The aim of the new company was to develop new engines in France that could then be licensed around the world.

Two years later, in 1948, the first licenses were supplied to engine builders.

In 1951, after its relocation at La Courneuve, the Société Générale de Constructions Mécaniques got equipped with the first test beds. The equipment, which enabled the company to speed up the development of a new range of engines, was later transferred to Saint-Denis and the subsequently to Saint-Nazaire.

In 1976, Alsthom-Atlantique was the flagship of French industry. The conglomerate became the majority, which also owns the Saint-Nazaire mechanical facility and a factory at Jouet-sur-l’Aubois, was renamed S.E.M.T. Pielstick after the widely known name of the company's founder.

In 2006, MAN purchased the shares belonging to MTU to become the sole shareholder of the company. Then, in 2010, the diesel engine and turbo machinery activities were merged. The S.E.M.T. branding remains, and is protected, but no longer appears as a company name.

The range of engines

The PC range of engines, the founding engine

The first PC1 engine was developed in 1951, and powered by heavy fuel oil in 1953. The first unit to go into series production was a six-cylinder, in-line engine (6 PC1 L) for the electricity generating plant of Bamako, Mali. With a bore of 400 mm, it developed 180 kW per cylinder. Its first marine application appeared in 1955, aboard the ship Borée (two engines).

The PC2 was launched at the start of the 1960s. Though it kept the same 400 mm bore, power output was increased to 310 kW per cylinder – an increase that became a regular feature of the engine's improvements in its subsequent versions: the PC2.3 in 1971, PC2.5 in 1973 and the 550 kW per cylinder PC2.6 in 1981. A dual-fuel version (gas and diesel) was also developed, while the range had its final addition in 1995 with the PC2.6B long-stroke engine. This final version featured a cast-iron engine mounting, a simpler design and a power output of 750 kW per cylinder – four times the power of the original model from 1953.

The PC3 engine with a 480 mm bore was launched in 1969, with a power output of 700 kW per cylinder.

The PC4 engine with a 570 mm bore appeared in 1972, producing 990 kW per cylinder, which increased with the PC4.2 version in 1981 to 1,215 kW per cylinder and with the PC4.2 B long-stroke model in 1985 to 1,325 kW per cylinder. In its 18-cylinder version, the latter model was one of the most powerful four-stroke engines on the market in its time.

The PA engine range, a miniature PC

The PA engines were high-speed units, running at more than 1,000 rpm. The initial PA1 and PA2 models could be seen as miniature versions of the PC engines, with a bore of 175 mm, and could be used for a wide range of applications – including powering submarines. The first turbo-charged version of the PA developed 46 kW per cylinder at 1,250 rpm.

Launched at the end of the 1950s and initially developing 110 kW per cylinder at 1,500 rpm, the PA4, with an initial 185 mm bore, was a completely new design. The work of Mr. Haug, it took the principles of being compact and lightweight, that were so cherished by Gustav Pielstick, to a new level. It would later be developed with a VG version (variable geometry combustion chamber) and subsequently with a 200 mm bore to increase the power. A dual-fuel version (diesel fuel and gas) would also be developed.

The PA4 VGDS with a twin-stage turbo to power naval ships was presented in 1978, generating 184 kW per cylinder. The final model in the range was launched 10 years later. This was the PA4 200 VGA for rail and naval applications, producing 165 kW per cylinder with a single-stage turbo. Specific versions for submarines were also developed: the PA4 185 SM, PA4 200 SM, and PA4 200 SMDS with twin turbo-charging.

The PA6, a multi-purpose engine

Plans for a completely new engine began to be laid from 1966 onwards. Launched as the PA6, it was designed to be the most powerful engine that could be fitted to a standard International Union of Railways (UIC) locomotive. The aim was to provide yet more power, at a time when diesel-electric traction still had a long way to go. The UIC approved the PA6 in 1971 and the first engines were produced the following year. A continuous process of improvement followed, with a range of different versions including the high speed PA6 BTC for naval ships in 1975, the PA6 CL long-stroke engine with reduced fuel consumption in 1981 and the PA6 STC, which used sequential turbo-charging for naval ships in 1988.

The final engines in the series would be the PA6 B and high-speed PA6 B STC in 1995, providing increases in power and overall performance. While these units did not enjoy commercial success in the rail market, for which they were designed, they proved to be highly popular for naval customers. The PA5, the ‘little brother’ of the PA6, was launched in 1981 to meet an initial market demand from the Japanese fishing fleet. A dual-fuel version would later be developed (diesel fuel and gas) for electricity generating stations.

The major installations

French Navy

SEMT Pielstick has provided PA and PC engines for the Georges Leygues, La Fayette, Floréal, Cassard and Horizon Frigates; A69 avisos; P400 patrol boats; the Jules Verne repair ship; the Durance type oil tankers; and the Foudre and Ouragan Landing Platform Docks. Nearly the entire French fleet, in the early 2000s, was equipped with SEMT Pielstick engines.


SEMT Pielstick has also been involved in a number of export programs, such as the Saudi F 3000 S frigates (Sawari II program) and the Sigma class frigates for the Moroccan Navy (2 x 20 PA6B STC). Thanks to Fairbanks Morse Engines, license holder in the United States, SEMT Pielstick engines have also been chosen by the US Navy, the largest and most demanding customer in the sector. The 16-cylinder PC2.5 STC engine has been selected by the US Navy for its San Antonio-class LPD 17 troop transporters, which are each equipped with four engines and can carry up to 800 marines. The PA and PC engines have enjoyed considerable success in countries around the world (including China, India, Britain, South Korea, Indonesia and Russia, along with the Japanese maritime safety agency) and are used by 60 navies to power their ships. It is a story that still continues today, thanks to the efforts of licensees.


Gustav Pielstick designed the MAN 40/46 engines, considered the best in their class at the time, for the U-boats of the German Kriegsmarine. After the war, SEMT enjoyed a considerable technological advantage in the field – which it maintained in the following decades. The PA4 engine was adapted for use by submarines, leading to the SM versions of the PA4 185 and 200. These were equipped with Hispano-Suiza compressors – given the particular constraints in terms of air aspiration and exhaust gases within a submarine. The compressor also minimized the pressure variations created by the sea swell, increasing the reliability of the engine and therefore the safety of the entire propulsion system.

Merchant shipping

Thanks to the network of licensees, the PA engines and the PCs in particular have enjoyed considerable international success since the mid-1950s in providing propulsion and electricity for merchant ships. Large ships (cruise liners, cargo ships and container ships) are traditionally equipped with medium-speed PC engines, while high-speed PA units are used in smaller vessels. Certain engines have meanwhile been designed for specific applications. Japanese licensee Niigata, for example, identified strong demand among the country's fishing fleet – requiring an engine that would fit the trawlers exactly. The result was the design and development of the ‘little brother’ of the PA6, called the PA5, with a 255 mm bore. The optimized cost and low fuel consumption of the unit made it a great success around the Japanese archipelago. The propulsion systems needed for the large cruise liners built in the Saint-Nazaire shipyards also required a tailored solution. The nine-cylinder PC20 engines developed for the Sovereign of the Seas (268 meters) were mounted on rubber pads to reduce noise and vibrations in the cabins.

Rail applications

Train locomotives have also been a major market for S.E.M.T. Pielstick engines. It was a new technological challenge for the design department as the power requirements of trains are far more varied than they are for ships. The “small” Piestick PA4 unit with a 185 mm bore was designed specifically for this market. Although it represents a limited activity today, rail transportation was a particularly large market in years gone by: 44,2% of all the engines produced in the history of S.E.M.T. were destined for locomotives.

Thermal power plants

Electricité de France began using S.E.M.T. Pielstick engines for its diesel-powered plants in the 1950s. EDF would subsequently remain a loyal customer when it later equipped plants in France's overseas territories and dominions with 18 PC4.2 V engines – which were recently replaced with MAN 48/60 and 51/60 Dual Fuel units. The Saint-Nazaire production site has been entirely re-organized and is now capable of producing 50 such engines a year. MAN decided to support the Saint-Nazaire site because of its direct access to the port, thereby easing the transportation of equipment to customers. The PC engines for diesel-fueled electricity generating plants have also enjoyed considerable commercial success in Japan, with its archipelago comprising numerous islands that need to be autonomous in terms of power production. Today, MAN Diesel & Turbo France is able to deliver turnkey thermal power stations with auxiliary power units ranging from 125 to 19,000 kW. With its expertise in the combined diesel cycle (diesel engine and steam turbine) and the ability to use a range of different fuels – such as fuel oil, bio-fuel, heavy oil and gas – these plants offer remarkable flexibility at an operational level.

Auxiliary power for nuclear plants

MAN Diesel & Turbo is a world leader in auxiliary power units for nuclear power plants. The units represent a key element in nuclear plant safety as they provide backup for its safety systems - should these lose their main source of power. S.E.M.T. Pielstick engines have been approved for such use in numerous countries because of their performance levels when taking over the supply of power, and also their reliability. They can even operate in the event of an earthquake or in extreme climatic conditions.


S.E.M.T. engines have been manufactured in many countries around the world. A total of 34 licensees produced its engines since the company started. Currently, there are eight: - Fairbanks Morse Engine – United States, - Doosan Heavy Industries & Construction – South Korea, - Shaanxi Diesel Heavy Industry – China, - Hudong Heavy Machinery – China, - JFE – Japan, - Diesel United – Japan, - Kawasaki Heavy Industries – Japan, - Niigata Power Systems – Japan. The licensing system provides opportunities in markets that would be inaccessible without a local partner, particularly in the nuclear and defense sectors. It can also lower the cost of the engines, depending on the country where they are manufactured.

Shareholder evolution

1987: The actions are shared in 3:

  1. 49% by Alsthom
  2. 25.5% by MTU
  3. 25.5% by MAN

1990: Shares are shared equally by Alsthom, MTU and MAN (33.3% each).

2006: 100% of Pielstick's shares are held by MAN and become the sole shareholder.

Key figures as of 12.31.2016

45 550 692: It's the amount of kilowatts delivered by all of the S.E.M.T. Pielstick engines produced since the company started.

24.8% of engines have been built in France whereas 75.2% of engines have been built abroad by licenses.

More than 15 000 engines have been manufactured to date.

373: it's the number of emergency diesel generating sets in service around the world, with a combined power capacity of 2.392 MW.

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