COVER STORY
supplemental designations, confirming that the correct supplemental designation, and the MSS SP-160 callout alongside it, makes it into the order before a component is ever sourced, not after it arrives.
Figure 4: A forged flange and tee fitting subject to HF supplemental designations.
• S78 for wrought fittings
• S62 for forged fittings and flanges
• S51 for valve castings
Figure 5 below maps each designation to its base ASTM specification: HF service starts at the purchase specification, and MSS SP-160 draws a specific distinction in who is responsible for it. The end user is the final owner who will operate the valve in HF alkylation service, while the purchaser is whoever places the order, whether that’ s the end user, an engineering, procurement, and construction( EPC) contractor, or a valve supplier, depending on the stage of manufacturing( MSS SP-160, § 2.3, § 2.6).
A component isn’ t treated as HF material unless the purchase specification explicitly calls it out as such. Increasingly, that means specifying to MSS SP-160 rather than to an individual material specification alone. These callouts on the purchase order are not automatic. Most commodity-grade quotes default to the base ASTM specification unless HF service is explicitly flagged at the time of inquiry. A purchaser working from a generic material description may miss the supplemental requirement entirely, ordering a straight A216-WCB casting, for instance, when the job actually calls for A216-WCB S51. MRC Global’ s technical sales team reviews HF alkylation orders for missing or mismatched
Getting the specification right is the first step
Every limit discussed here, the residualelement thresholds under API RP 751, the valve-level requirements MSS SP-160 adds on top of them, and the supplemental ASTM designations that tighten the base material specification, exist on paper before it exists in a delivered component. None of them protects a valve in service if a supplier ships against a generic material description instead of the HF-specific one. Getting it right is within a purchaser’ s or end user’ s control from the start, citing the right standards by name and working with a supplier who treats those callouts as requirements rather than boilerplate. MRC Global’ s technical sales team’ s reviewing of each HF alkylation order is where that work begins. Specifying correctly is necessary, but it isn’ t sufficient on its own. Confirming that a component meets what was specified through methods such as PMI and OES testing, and through the same documentation and traceability discipline applied to the pipe, fittings, and flanges around a valve and not only the valve itself, is a separate, ongoing responsibility. A related article on how MRC Global built that verification process, inside its Low-RE and Critical Materials Testing Lab in La Porte, Texas, will appear Valve World, Vol. 35, December 2026.
Figure 5: ASTM base specifications and HF supplemental designations.
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