Lethal Service - Quick Guide
Date:Oct 7, 2011
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...
The following Code Cases refer to lethal service for VIII-1 vessels (2007)
- 1750-20(g) - A126 not to be used for prvs, or rupture disks.
- 2249 - Furnace Brazing
- 2318 - slip on flanges in lethal service
- 2321-1 PWHT of P4 and P5A materials
- 2324 - Ultrasonic inspection
- 2334 - single fillet lap joint tubesheet to shell connection
- 2346-1 & 2537 - Alternative rules for SE and F&D head to shell attachment
- 2369 - Testing of covers separate from vessels
- 2377 - RT of SA-612 steel
- 2421 - Single fillet joints in Heat exchanger tubes
- 2437 - Diffusion bonded heat exchangers
Special lap joint stub end for lethal service
All partial penetration nozzles are prohibited
All figure UW-13.2 corner welds are prohibited
No slip on flanges
Disclaimer: This material is provided for educational uses only. Only ASME can make code interpretations.