Overpressure Protection for Temporary Equipment
In our experience, rented, leased or purchased temporary equipment as well as vendor-supplied skids that are intended for either temporary or normal use, have been found to have numerous issues pertaining to the overpressure protection where the design is often overlooked or provided by a vendor without analyzing the hazards associated with the operator’s process to be connected to the skid. Some of these issues are documented in the conference proceeding by Heil and Pack, “Vendor Supplied Equipment: Ensuring PSV design meets PSV spec”.1 Here are a few examples of common issues:
- Operator tends to rely on the vendor for overpressure protection design as their priority is to meet design operating requirements for packaged equipment
- Supporting engineering design documentation for pressure relief device installed by vendor is not available
- Design of overpressure protection by vendor is not in compliance with industry or operator design standards
- Design of overpressure protection by vendor may be deficient as their engineers may be inexperienced in relief system design or do not have sufficient knowledge and information from Operator for the process and interconnected equipment outside of the packaged skid, resulting in oversight of scenarios
- Vendors of packaged equipment often install non-API 526 pressure relief devices, which are more prone to excessive inlet and/or outlet pressure drops
As indicated by Heil and Pack, “As has been demonstrated through the preceding examples, when not fully defined through clear Operator expectations and Packager [Vendor] accepted responsibilities, the relief system design basis for packaged equipment skids can be affected.” Many of the vendor supplied equipment are constructed to API or similar standards, in accordance with operator procurement specifications, which quite often do not specifically address the pressure relief requirements for equipment, providing only a reference to API Standards 520 and 521 (if any at all). Regardless, it is important that operator and vendor work together to ensure adequate overpressure protection is provided for the temporary equipment or skid.
A pragmatic approach to this situation may be to identify the temporary or skid-mounted equipment which are common versus uncommon, and/or to stratify them on a risk basis. For commonly used equipment, it may be cost-effective to review the procurement requirements to ensure overpressure protection is being specified and provided in accordance with corporate standards. Perhaps for some systems, a simple checklist to verify against upon receipt of the equipment would suffice.
For uncommon equipment, a risk-based approach may be useful. For those systems with lower risks, a simple checklist could be used to verify overpressure protection. For those systems with elevated risks, more rigorous evaluation is warranted, whether that be with a separate design analysis for longer-duration installations or a MOC-type review for shorter-duration installations.
 Heil JE, Pack BA. “Vendor Supplied Equipment: Ensuring PSV Design Meets PSV Spec”. Proceedings of the Lawrence Reid Gas Conditioning Conference; Norman, OK; February 2014.