EnerMech bought out the entire equity of Norson, held by its management, Aberdeen Asset Management and other shareholders. EnerMech said Norson's management team, led by managing director Gordon Telfer, would remain with the firm as "a key element in growing the business".
Norson's 90 staff will transfer to EnerMech's headquarters in Howes Road, Aberdeen, later this year.
The combined 60m firm merges EnerMech's cranes, lifting equipment, hydraulics rental and training services to the offshore oil and gas sector business with Norson's global hydraulic pipework business.
In addition, EnerMech will invest a further 2m to roll out Norson services to EnerMech bases in Dubai, Singapore, West Africa and Australia. Norson's base in Houston will also extend EnerMech's reach in North America, the Gulf of Mexico and Brazil.
EnerMech managing director Doug Duguid said Norson was a "well-run, profitable business with the potential for further growth".
He added: "Synergy is an over-used word, but in this case Norson's expertise and products dovetails extremely well with our existing business lines.
"Norson has a lot of clients in the drilling and subsea construction sectors which we can tap into, while its reputation for designing and building top class hydraulic systems will help us attract new customers in international markets."
Norson itself was subject to a multi-million pound management buy-out in 2007, backed by AAM.
Norson's Telfer said: "EnerMech has the capital resources and international expertise which provides Norson with the opportunity to penetrate new markets.
"It's envisaged our workforce will increase and the deal brings exciting opportunities for existing and future employees."
Backed by specialist venture capital firm Lime Rock, EnerMech last year acquired Pavitt Energy and Scotia Oil Services in the Middle East and opened new offices in Doha, Singapore and Australia. Total equity investment in EnerMech by Lime Rock and the company's management team following the latest deal is 41m.