API RP 691
Risk-based Machinery Management
|Publication Date:||1 June 2017|
This recommended practice defines the minimum requirements for the management of health, safety, and environmental (HSE) risks across the machinery life cycle. It shall be applied to the subset of operating company and/or vendor defined high-risk machinery.
Unless otherwise specified, the following criteria shall be used for initial risk screening to identify potential high-risk machinery for which this recommended practice will be applied:
a) hazardous gas or liquid services as defined by jurisdiction, appropriate regulatory body, and/or operating company standards or specifications,
b) services operating at temperatures >350 °F (177 °C) and having design or specified off design operating pressures >80 % maximum allowable working pressure (MAWP),
c) services operating at temperatures >400 °F (204 °C),
d) components and subcomponents having technology readiness levels (TRLs) < 7 whose failure may lead to a loss of containment and/or a loss of functionality that could lead to a potential process safety event (see Table 1),
e) liquid services operating at pressures in excess of 600 psig (41.4 bar),
f) liquid services having specific gravities less than 0.5.
It is acknowledged that most operating companies and vendors may have existing risk management processes. This recommended practice is not written to replace or invalidate company practices but is meant to supplement them to provide safe working and living environments for facilities and surrounding communities. Operating companies (i.e. Sections 5, 6, 7, and 8 for design, installation, and operating purposes) or vendors [i.e. in Section 4 for research and development (R&D) and product development purposes] can use their own initial risk screening criteria where these have been found to be effective or the criteria recommended above.
NOTE 1 Typically only between 10 % and 20 % of machinery falling within any given initial risk screening will be considered API 691 Machinery. This can include a subset of "critical," "unspared," "special purpose," "prototype," and/or worst actor machinery. Risks can include loss of containment of hazardous fluids, loss of functionality, high energy releases, etc.
NOTE 2 Applicable international (e.g. GHS ) or national (e.g. OSHA 1910.119, API 570 , Class 1, etc.) hazardous service classifications are typically defined within operating company specifications.
NOTE 3 Operating companies and vendors can choose to apply this recommended practice to machinery not covered by existing API standards (e.g. hyper compressors).
The following machinery protection and safety standards shall be applied to new API 691 Machinery where applicable:
a) API 670;
b) IEC 61508-1, IEC 61508-2, and IEC 61508-3;
c) IEC 61511 (Parts 1, 2, and 3) or ANSI/ISA-84.00-2004 (Mod IEC 61511);
d) IEC 62061 or ISO 13849-1 and ISO 13849-2.
Other standards and technical reports may be used to further assist in the application of this standard including:
a) ISO 12100, 
b) ISO/TR 14121, 
c) VDMA 4315, 
d) IEC 60812, 
e) IEC 64244-3. 
This recommended practice is intended to be used by operating companies, their designated responsible parties (DRP), and vendors that are identified as potentially operating at high risk. It is applicable to both new (Sections 4 to 8) and existing (Section 8) installations.
NOTE This can include some supporting process equipment, for example, knockout drums, instrumentation, etc. that are located off-skid.