Standard Defining Appropriate Overpressure Protection

[HotPotato]

After several years in the Industrial Gas industry, I am now working in a pharmaceutical facility that makes use of many positive displacement pumps. There are several instances where a positive displacement pump does not have over-pressure protection. Since pharmaceutical facilities do not handle high pressures, most personnel do not have a lot of experience with high pressure safety systems. I have been asked if a single pressure switch would suffice to protect a system from an over-pressure scenario.

From my experience, I know that relying on a single pressure switch to protect from over-pressure scenario is poor engineering practice but I would like to refer to a standard that explicitly states this. Is there any US standard, preferably enforced by law, that states a rupture disk or relief valve is the only acceptable protection? Any type of SIL device/systems are not an option for this type of facility. Pressures are around 100-150psig.

 

[georgeverghese]

Pressure vessels designed to ASME standards, for example, require mandatory overpressure protection with an RV or eqvt, as described in one of the appendices in ASME Div 1, section 8. The same may be required for piping systems designed to ASME B31.3. Adding a high pressure trip is normally considered good practice, and not enforced by law.

 

[shvet]

Pressure switch for overpressure protection is an acceptable measure according to annex E API 521 6th ed. ASME VII still disagree with API 521.

 

[The Obturator]

Just to add; If designed to ASME VIII PRD Pressure Relief Device required if pressure 15 PSIG and above, If EU following PED then 0.5 barg min.

Per ISO, only the term Safety Valve is used regardless of application or design.

 

[don1980]

ASME Sec VIII (paragraph UG 140b) authorizes the use of HIPS (also refereed to as HIPPS) instrumentation as supplementary or stand-alone protection from overpressure. As mentioned by Shvet, guidance for implementing HIPS/HIPPS is found in API 521 Annex E (note that there's no conflict between API 521 and ASME sec VIII).

API-521 doesn't permit the use of non-HIPS instrumentation for preventing overpressure.

 

[mk3223]

IMO, the overpressure protection of the equipment or piping system is part of the OSHA safety requirements. The number of the safe guards of the system may be analyzed by using a safety matrix. It depends on the severity and likelihood of the event according to the system design and operation experience.
The single switch for the overpressure protection my be acceptable if the risk is very low, i.e. low severity and low probability. Be aware of the low probability event which may be a high risk for the operation.

 

[georgeverghese]

The ASME and its equivalents in other countries (DIN, BS, JIS etc) are mandatory codes of practice enforced by law, while API Recommended Practices are not.