English to Spanish Tech/Engineering Mechanics / Mech Engineering Steam boilers

Buenas noches,

El texto a continuación forma parte de un manual de una caldera de vapor.
He tratado de encontrar el significado del término "boiler proper",pero hasta el momento no he tenido éxito. Alguien con experiencia en el tema?

A continuación un par de referencias al respecto:

Boiler Proper refers to the central component of heating system responsible for transforming water into steam.

Boiler proper or "pressure vessel" means the internal mechanism, shell, and heads of a boiler or pressure vessel terminating at:...

(10) "Boiler proper" or "pressure vessel" means the internal mechanism, shell, and heads of a boiler or pressure vessel terminating at: (a) the first circumferential joint for welded end connections; (b) the face of the first flange in bolted flange connections; or (c) the first threaded joint in threaded connections.

Creo que puede haber una traducción más adecuada que "recipiente a presión".

A continuación el término en el documento que estoy traduciendo:
Dissolved Oxygen: Oxygen that is dissolved in the feedwater will cause the steel
in the boiler and the feedwater system to be attacked by the water in a manner
described as “pitting”. The pits that are produced can vary from tiny depressions
to holes large enough to penetrate the boiler metal and are usually covered with
tubercles of iron oxide. Once pitting starts, it may be extremely hard to arrest.
Pitting can proceed at a surprisingly rapid rate and can occur not only in the
**boiler proper**, but also in pre-boiler equipment such as ecomomizers, feedwater
tanks, and feedwater lines.

Una vez más y de antemano, muchas gracias por todos sus aportes.

Saludos,