ASME Lethal, Sour and Category M Services

MECHANICAL ENGINEERING

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LETHAL, SOUR AND CATEGORY-M SERVICES

March 18, 2016

What is a Lethal Service? ASME Section-8 Div-1 has two similar definitions for Lethal Services o UW-2 (a): “When 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” o End note-65: “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” How to determine if the service is Lethal? It is up to the end user to determine if a service is lethal, based on the user’s experience and criticality of the services as per the above definition. The code does not specify any criteria to determine lethal services. Below are few references from the code: o UW-2(a): “it shall be the responsibility of the user and/or his designated agent to determine if it is lethal. If determined as lethal, the user and/or his designated agent shall so advise the designer and/or Manufacturer” o Appendix NN Table NN-6-5:

Note: H2S process services are not the only services which are lethal. What is a Sour service? NACE MR0175 / ISO 15156-1 (3.19) defines Sour services as: o "Exposure to oilfield environments that contain H2S and can cause cracking of materials by the mechanisms addressed by NACE MR0175" Note: ASME Section-8 Div-1 and B31.3 does not say anything about sour services. How to determine if the service is Sour? The amount of H2S that can term the service as Sour can also be found in NACE MR0175. What is the difference between Sour and Lethal? Sour and Lethal are not the same. A service is termed as Sour when its H2S content can affect the base material & the weld. Whereas, lethal relates to toxic services harmful to humans. What is Category-M service? Category-M is a service category specified in ASME B31.3. Prepared by Besant Varghees ([email protected])

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MECHANICAL ENGINEERING

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LETHAL, SOUR AND CATEGORY-M SERVICES

March 18, 2016

As per B31.3 300.2, Category M Fluid Service is defined as a fluid service in which both of the following apply o “the fluid is so highly toxic that a single exposure to a very small quantity of the fluid, caused by leakage, can produce serious irreversible harm to persons on breathing or bodily contact, even when prompt restorative measures are taken” o “after consideration of piping design, experience, service conditions, and location, the owner determines that the requirements for Normal Fluid Service do not sufficiently provide the leak tightness required to protect personnel from exposure” So, is Lethal same as Category-M service? Lethal (Section-8 Div-1) and Category-M (B31.3) definitions looks similar, but we cannot interchangeably use it. Lethal is only for pressure parts designed as per Section-8 Div-1 and Category-M is only for components designed as per B31.3. ASME B31.3 has given an explanation for this difference through Interpretation No.1-73, which says: o Interpretation 1-73: Question: “Is a Category M Fluid in B31.3 the same as a lethal substance in the ASME BPV Code Section VIII?” Reply: The Committee points out that the term used in B31.3 is Category M Fluid Service, not Category M Fluid. This distinction is very important in understanding the intent of B31.3. Fluid Service is much broader in concept in that it encompasses the complete handling and control of the fluid. It takes into consideration not only the fluid properties (such as flammability, toxicity, etc.) but also the service conditions (such as pressure, temperature, quantity, location, etc.) as they affect all aspects of the piping system. Finally, in developing Category M Fluid Service, it was not the intent of B31.3 to parallel the lethal substance reference in the ASME BPV Code Section VIII, Division 1. How to determine if a fluid service is Category-M fluid service? o Unlike Lethal, B31.3 has set of rules for Category-M (Fig M300 see below), and those fluids falling to those set of rules MAY be termed as Category-M fluid service. But still its subject to the owners discretion to follow those rules.

What consideration shall be taken while designing a Lethal service pressure vessel? UW-2 restrictions: o UW-2(a) and UW-11(a)(1) - All butt welds shall be 100% radiographed

Prepared by Besant Varghees ([email protected])

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MECHANICAL ENGINEERING

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LETHAL, SOUR AND CATEGORY-M SERVICES

March 18, 2016

o

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 o UW-2(a) - Post weld heat treatment is required for CS and Low Alloy o UW-2(a)(1)(a) - Category A welds shall be type 1 only (butt welded with no permanent backing strip) o 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 o Interpretation VIII-I-98-23 - Category D welds (typically nozzles) shall be full penetration. o UW-2(a)(1)(c) - Category C joints for stub ends have a long list of requirements o UW-2(a)(2 and 3) - Heat exchangers have a long list of requirements o Read all of UW-2 for more restrictions... Other Rules o U-2(a)(2) - The user determines if the service is lethal. o UG-16(5)(a) - Air cooled and cooling tower heat exchanger tube walls to be 1/16" min. o UG-24(6) - Casting RT requirements. o UG-25(e) - No telltale holes. o UG-99(g),(k) - Hydro test visual leak inspection cannot be waived. Do not paint prior to the hydro test. o UG-100(d)(4) - Pneumatic tests cannot be used for lethal service vessels, but also see code cases 2046-2, 20552, 2407 regarding pneumatic instead of hydrostatic testing o UG-116(c) - "L" stamping must be added to the nameplate. o UG-120(d)(1) - "lethal service" is added to the data report o UW-2 - Service Restrictions - main source of info on Lethal Service (see lots more from UW-2 below) o UW-11(a)(1) - All shell and head butt welds to be 100% RT o Fig UW-13.5 - One possible lap joint stub end configuration - see also interpretation BC-79-680 / VIII-80-111 o UB-3 - Brazed vessels shall not be used o UCS-6 - Do not use SA-36, 38W or SA-283 o UCS-79 - PWHT and extreme fiber elongation - read for rules when heat treatment is required o UCI-2, UCD-2 Cast iron and ductile cast iron vessels are not allowed. o UIG-2(c) - Metal parts for graphite vessels are to be designed to UIG requirements o UIG-23(b) - Factor of safety for lethal service o UIG-60 - Lethal service o UIG-99 - Lethal service pressure tests o ULW-1 & ULW-26(b)(4) - Layered vessels lethal restrictions apply to the inner shell and heads only o UHX-19.1(b) - Heat exchanger markings o Appendix 2-5(d) & 2-6 - Maximum Flange Bolt Spacing o Appendix 2-14(a) - Mandatory flange flexibility o Appendix 7-1, 7-5 - Steel casting examination for 100% quality factor o Appendix 9-8 - if the jacket does not carry lethal substances, lethal service restrictions do not apply to it o Appendix 17-2(a) - Dimple jackets will not contain lethal substances o Appendix 35-3(c) & 35-7(d) - Mass production rules o Appendix W Table W-3 - Filing out the U forms o Appendix KK (note 12) - Filling out User Design Requirements forms o Appendix NN Table NN-6-5 - User or designated again determines if the contents are lethal o End notes 65 - Definition of lethal service

Prepared by Besant Varghees ([email protected])

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