In engineering lingo, the steam boiler is a 'fired pressure vessel,' the pulp digester an 'unfired pressure vessel
The ASME Boiler and Pressure Vessel Code was first published in 1915, and the initial edition of the Unfired Pressure Vessel
Code, Division 1, was distributed in 1925.
'When developing the certification programme, we took into account the requirements of the Pressure Equipment Directive and the normative requirements for unfired pressure vessels
, but also added in our own very extensive experience with materials and welding technology', says Gunther Kuhn, Head of Product Management in the Plant Safety business unit of TUV SUD Industrie Service GmbH.
1923 Code for Unfired Pressure Vessels
. 1924 ASME publishes two American Engineering Standards Committee standards--Machinery Shafting and Transmission Shafting.
The basic principles of supervised and unsupervised pattern recognition (PR) techniques for classification of acoustic emission (AE) data are presented herein together with successful applications of the techniques, for AE condition-assessment of unfired pressure vessels. The paper discuss the basic principles of supervised classification, consisting of a learning process, where representative AE data are used as examples to train a classifier for subsequent classification and automatic evaluation of unknown AE data.
Acoustic emission (AE) testing of unfired pressure vessels is usually performed during controlled stimulation  where mechanical or thermal stresses give rise to AE signals from active discontinuities.
The Figure 32, 42, and 42A valves are said by the manufacturer to be excellent for use on steam boilers, steam service on unfired pressure vessels
, accumulators, cleaners, and distillers as well as for air, gas, and vapors on compressors, receivers, burners, dryers, and other piping systems.