Lethal Service - Quick Guide

File:PVE-3856
Date:Oct 7, 2011
By:LB

Requirements for lethal service are scattered through VIII-1, the code cases and the interpretations. ASME VIII-1 section UW-2 (2007 edition) has most of the requirements for lethal service. Two definitions of lethal service are provided in UW-2:

[A] vessel is to contain fluids of such a nature that a very small amount mixed or unmixed with air is dangerous to life when inhaled[.]

By "lethal substances" are meant poisonous gases or liquids of such a nature that a very small amount of the gas or of the vapour of the liquid mixed or unmixed with air is dangerous to-life when inhaled. For purposes of this Division, this class includes substances of this nature which are stored under pressure or may generate a pressure if stored in a closed vessel.

It is up to the user to determine if a service is lethal. We at Pressure Vessel Engineering do not determine if the vessel service is lethal (but we might have opinions based on previous jobs).

When it has been determined that a vessel is in Lethal Service, some of the following code sections will apply. Other code sections might also be required.

UG-16(5)(a) - Air cooled and cooling tower heat exchanger tube walls to be 1/16" min.
UG-24(b)(5)(a)- Casting RT requirements. UCI-2, UCD-2 Cast iron and ductile cast iron vessels are not allowed.
UG-99(g),(k) - Hydro test visual leak inspection cannot be waived. Do not paint prior to the hydro test.
UG-100(d)(4) - Pneumatic tests cannot be used for lethal service vessels, but also see code cases 2046-2, 2055-2, 2407 regarding pneumatic instead of hydrostatic testing
UG-116(c) - "L" stamping must be added to the nameplate. UG-120(d)(1) - "lethal service" is added to the data report
UW-2 - Service Restrictions - main source of info on Lethal Service (see lots more from UW-2 below)
UW-11(a)(1) - All shell and head butt welds to be 100% RT
UB-3 - Brazed vessels shall not be used
UCS-6 - Do not use SA-36, 38W or SA-283
UCS-79 - PWHT and extreme fiber elongation - read for rules when heat treatment is required
ULW-1 & ULW-26(b)(4) - Layered vessels lethal restrictions apply to the inner shell and heads only
UHX-19.1(b)- Heat exchanger markings
Appendix 2-5(d) - Maximum Flange Bolt Spacing
Appendix 2-6 - Bolt Spacing Correction
Appendix 7-1, 7-5 - Steel casting examination for 100% quality factor
Appendix 9-8 - if the jacket does not carry lethal substances, lethal service restrictions do not apply to it
Appendix 17-2(a) - Dimple jackets will not contain lethal substances
Appendix W Table W-3 - Filing out the U forms

More from UW-2:

UW-2(a) and UW-11(a)(1) - All butt welds shall be 100% radiographed
UW-2(a) - ERW pipe (like some grades of SA-53) is not permitted but interpretation VIII-1-01-118 says it is acceptable if the long seam is fully radiographed
UW-2(a) - Post weld heat treatment is required for CS and Low Alloy
UW-2(a)(1)(a) - Category A welds shall be type 1 only (butt welded with no permanent backing strip)
UW-2(a)(1)(b&c) &Interpretation VIII-1 92-211 - Category B & C welds shall be type 1 or 2 only (butt welded). No slip on flanges! No Figure UW-13.2 Flange or Head to Shell attachments
Interpretation VIII-I-98-23 - Category D welds (typically nozzles) shall be full penetration.
UW-2(a)(1)(c) - Category C joints for stub ends have a long list of requirements
UW-2(a)(2 and 3) - Heat exchangers have a long list of requirements
Read all of UW-2 for more restrictions...